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Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]
20

Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

(OP)
Indonesian 737 Max 8 - Splashed

Most reports I've seen mention the aircraft had an 'undisclosed issue' before take-off. Does anyone know what that was?

Surely the crew was in contact and reporting something during the relatively long disaster.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Seems that there had been some technical issues reported for the prior flight, people reporting unusual engine noise, etc. Can't find the link to the article right now.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Couple of days ago, the BBC was reporting a discrepancy between captain's and first officer's altitude and ASI displays.

A

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

One recorder has been recovered, they didn't say which one.

Another thing not reported yet that I have seen is whether the same crew was on the doomed flight as on the one before. There were some issues on that flight, and were said to have been fixed. If the pilots carried over to this flight, they can't help, but if they were relieved, they could probably shed some light.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Here's a link to a forum where lots of aviation experts are discussing this crash. I follow the forum regularly and you'll get breaking there first.

https://www.airliners.net/forum/viewtopic.php?f=3&...

Brad Waybright

It's all okay as long as it's okay.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Reports are that the pilot of this aircraft's previous flight issued a "Pan Pan" alert, requesting to return to the airport, then cancelled it when the plane started flying satisfactorily. It was also reported that passengers on that previous flight saw a pilot walking down the aisle with a big manual. Before this crash, Lion Air had a seven star safety rating, now reduced to six stars.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

(OP)
A prior flight passenger said the plane dropped suddenly "panicking the passengers". Seems like the next load of passengers got the complete ride.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

I think it is highly unusual, maybe in violation of aviation rules in most countries, for a Pan Pan alert to be overridden with the flight continued as if nothing had happened.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (hokie)

I think it is highly unusual, maybe in violation of aviation rules in most countries, for a Pan Pan alert to be overridden with the flight continued as if nothing had happened.

Possibly against the airlines internal operational specifications but not against any aviation rules I'm aware of.

Pilots actually frequently cancel emergencies. For example; sudden icing beyond the capabilities of the airplane to fly through. Declare emergency and use pilot authority to descend without getting clearance from ATC. Get below the icing and then you can cancel your emergency and continue on like nothing happened. You will of course have to explain later why you called an emergency and could get in trouble if they find you either caused an emergency through reckless action or canceled an emergency when the emergency still existed.

Pan-pan is even more likely to be canceled; it essentially indicates you have a priority situation that requires special attention. Something like a broken radio or a standby instrument failure or a jammed landing gear. It's not an emergency yet but you may need something special (direct route to destination, going into a holding pattern, emergency equipment standing by, etc.), if you're able to fix the problem in the air you can let ATC know that you fixed it and proceed on.

Clearly they made a mistake to continue on. It's just a matter of whether that mistake was reasonable and/or not their fault.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries https://www.facebook.com/AmericanConcrete/

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

There have been a number of instances of instrument failure due to clogged pitot tubes. Insects? But surely properly trained pilots would be able to overcome that type problem.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

6
hi all just registered to answer some questions

I used to be Finite Element Mech Eng in a previous life. Now I fly aircraft for a living.

I am not rated on the 737 only Dash 8 Q400 and previous Jetstream 31/32/41. The Q400 is a modern digital efis system aircraft and the Jetstreams old analogue tech.

First of all the emergency declaring. There is nothing stopping you trying to cancel if you sort out a problem. But its a two way thing once ATC knows you have an issue they can adjust the emergency level as they see fit and the pilot has no control over it. I won't go into the ins and outs of various situations but I have in the past declared and then cancelled and continued to destination and even operated the next flight immediately. 2 mins filling a report out and not heard a thing about it again. Also somethings such as Hydraulics failures are major issues on certain aircraft types and on others such as the Jetstream its more of an annoyance. This is to do with how the controls are powered or not in the case of the Jetstream. BUt if ATC hears anything to do with hydralic failure they will presume the worst thinking you going to go off the end of the runway due to needing to do a flapless high speed approach and have no brakes or steering on the ground. Jetstream we would pump the gear and flaps down, land and taxi using the prop reverse and front wheel castoring. Not a huge issue.

Instrument failures are a bit of a bitch. Analogue instrument aircraft in some ways are easier to trouble shoot and work out what's wrong and deal with.

Digital aircraft with efis the instrumentation comes from the airdata computers which take the environmental data and anther box does magnetic heading and navigation and displays it on the screens. There are at least two and they cross reference each other and when they disagree they tell the pilots. There is also a back up system which has its own pitot and static system and is run on a backup electrical supply with sperate battery support for if the main electrics go down.

What the pilots sees if something goes wrong is xxxxxx mismatch on the primary flight screen it won't trouble shoot. You then have to go into a quick reference handbook to reconfigure the displays to remove the faulty data input after comparing the 3 information sources and hopefully going with the two that agree. Its a two person check and double check. One person is meant to fly the machine the other one trouble shoots.

Now the departure is high work load and everything has to work towards getting away from the ground. The further away from the ground you are the more time and space you have to sort things out. Something happens below minimum safe altitude and you have a problem.

Now not all pilots think the same way, as an engineer flying a plane is just an energy equation which you can change the variables using the controls. So what to do is very logical to me with the flight profile. Your just playing with 4 variables thrust drag lift and weight.
The if you stick the nose at an up angle to the horizon with a set amount of thrust and the wings level it will climb within a range of speeds depending on weight. You don't actually need to know your airspeed to know you are safe. This to me is glaringly obvious and how I have treated instrument failures in the past from single engine piston right the way through to the 30 ton q400 (although I haven't had a problem with the Q's instruments yet with a mismatch). It works every time. To be honest its my normal method of flying pitch power equals performance. The speeds vary with weight but what your actually doing is setting a most efficient angle of attack which never changes.

Now other pilots brains don't seem to work the same way or as fast working out what's wrong. They "chase" the needles so they apply control inputs to make the numbers right. Once the numbers are right they then realise that the other data is not as expected then after a period of recognition then transfer to other methods of defining the flight profile. Now this goes back to the very first lessons flying how they fly. Personally when I was a flying instructor I didn't give my students any instruments and they had to learn to look out the window for attitude and set the power by ear. Then when they had that sorted they got the instruments. But because the habit was set initially they were not fixated on airspeed or other instruments depending what they were doing. Just attitude and power. Flying in cloud with the attitude indicator failed is another issue but we can do it.

This dealing with instrumentation failures is a hot topic in the sim sessions and has been since the Air France AF 477 accident.

Please note in no way am I inferring anything to do with this incident, At least once a year depending on the training syllabus sometimes more there will be an item in the sim to do with instrument failures. The low level just as the gear comes up are shall we say interesting. Personally I learn more about dealing with the human side of things during them with the reaction of the other pilot than I do from the actual handling of it. You can have two people with completely different ideas what's actually happening and what to do to fix it. And what you don't want is two people fighting over control inputs that's always fatal.

Most incidents are a combination of human and equipment, we will have to wait until the CVR and FDR are analysed to see what actually happened and no doubt the year after next there will be something in the sim training syllabus so we can all learn from it.





RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Thanks for sharing that with us, Alistair_Heaton. Very good perspective on the challenges and responses of properly trained pilots.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Avionics trouble shooting is always a problem as a lot of the time they test out SATIS on the ground and only show issues when the aircraft is in flight. vibration thermal expansion pressure changes are all factors.

Thankfully these days most machines have huge number of variables data recorders which get downloaded every 30 hours of flying anyway. They record stupid numbers of variables from the primary flight instruments through to the amount of times the toilet pump is used.

This data is used to monitor the pilots performance ie they run it all through a computer after its downloaded and checks to see if we have been sticking to SOP's or handling the aircraft in a none approved manner.
The other side is all the tech data for the engines and other systems. At least these days a tech problem the technicians can see the raw data instead of having to use pilot reports of problems. We also have a bookmark ability in the cockpit so if the engines fart or something weird happens we can press it and it dumps a marker in the datalog so it flags where in the 30 hours of data the issue occurred.

There are all sorts of cultural issues going on as well and shall we say philosophy's. I am lucky that I work for a company that the CEO was a pilot in his younger days and has dictated a clean techlog policy.

tech faults with aircraft get stuck into 5 classes.

AOG plane grounded until its fixed

A requires fixed in a small number of flights or time period.

B 3 days

C 10 days

D 120 days.

Its all control by a thing called minimum equipment list the more safety related the issue the shorter the period there is to fix it. If the problem is not mentioned in the MEL then your grounded.

Clean techlog means that the problems are fixed ASAP and things are not aloud to build up or left until the end of the limit. It means the engineering stores have to carry a huge number of spares which some company's would only order on demand knowing that they could get them inside the MEL limits. It costs money. But... I have only had to ground an aircraft down route twice in 2 years/1000 flights working for them. We are at the top of the league tables for on time departures and its a rare event with have to cancel a flight due aircraft tech. For me its obvious that his policy works. If its more cost effective than ordering on demand I really don't have a clue.

Training we spend 25% more time in the sim that legal min and also have 20% more ground school every year.

Some pilots are really not so lucky. Every entry in the techlog is an argument and training is considered a box ticking exercise. I really don't have a clue what this company's operating philosophy is like.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Any chance you could share what airline that is?

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

It may not be one selling tickets. Several years ago I’d heard from a pilot on one of the major carriers that the FedEx pilots got far more simulator time than any of the people haulers.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

New posts on airliners.net forum cite a recent press conference stating that the previous 3 flights experienced unreliable airspeed data.

Brad Waybright

It's all okay as long as it's okay.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (hokie)

But surely properly trained pilots would be able to overcome that type problem.

Short answer, yes. I'm not trained in large aircraft but am an instrument rated pilot so can share generalities. Pilots are definitely trained to fly without accurate airspeed or altimeter indications. I've actually had an in-flight altimeter failure due to water getting into the static air port during a foggy day. Quick fix as the plane was equipped with an alternate static air system, so it was a non-emergency. Generally these can be trained for safely and resolved without issue. You may have even been on a flight that had a failed instrument in-flight and not even known.

That said, instrument failures can be some of the most dangerous problems in aviation because they're sudden, possibly intermittent, and difficult to diagnose in a chaotic situation. There are redundancies of course, but the redundancies are not always complete replacements for the failed instrument. I'm not qualified to talk about the full procedure in a large, modern airline, but generally the procedure is to identify the instrument giving false readings, disable or ignore it (hard to do!), and utilize reliable alternative sources of info of which there should always be at least one. The plane will keep flying just fine but it becomes much harder to ensure the plane can be flown safely by reference to instruments alone. Due to this danger the systems are very robust and capable, but it still isn't perfect. A lot of flight training is spent focusing on preparing for sudden instrument failure.

Air France 447 was the extreme example of sudden instrument failure essentially startling the crew into an improper response, combined with some shortcomings in the design of the Airbus: https://en.wikipedia.org/wiki/Air_France_Flight_44...

Not sure if that happened here as well.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries https://www.facebook.com/AmericanConcrete/

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Alistair_Heaton and TehMightyEngineer have both touched on an important point when it comes to the pilot/machine interface for diagnosing problems in the stress of an emergency. Some instrumentation, at least with regard to the signals/data, are closed loop systems. For example, GPS. The GPS satellites contain data streams that works with the on-board receivers and the mix of various GPS satellites being used, typically 4-5 satellites for the heavy iron on which I have most of my experience. The GPS receivers on-board and the satellites in the constellation being used can talk back and forth to detect, isolate, ignore and/or call up redundant satellites without pilot intervention. Thus the data presented to the pilot is reliable unless a flag and/or warning notifies the pilot not to use the data.

Air data systems are (at least as far as the data provided to the pilot) not closed loop systems. What I mean is there is no satellite constellation, ground station, airborne station or any other system in place outside and independent of the aircraft against which the air data system can compare what it THINKS is correct, and thus no feedback outside the aircraft itself to say to the air data system, "Whoa, the data you are feeding to the pilot sucks, throw a flag!"

Thus the air data systems can really only compare against each other. On some aircraft there are actually four air data systems: Pilot, CoPilot, Standby and Alternate. This gives a lot of redundancy unless the situation that is affecting one system affects all systems in a similar manner.

To illustrate: In a GPS constellation the probability (I don't have hard data in front of me, using relative terms) is very unlikely that more than one satellite will develop the same malfunction at the same time as they are thousands of miles apart and fully independent from each other. However, even on an aircraft with four air data systems, if all the pitot tubes and/or all of the static ports are affected in a similar manner by the same phenomenon (say for example rapid onset of icing at altitude), the various systems still agree with each other even though all of the systems are now lying to the pilots.

Of course physical separation on the exterior of the aircraft and other means (software processing) are used to try and provide as much independence as possible along with opportunities to find deviations that can provide warnings to the crew, but it is not as easy to provide independent comparisons between on-board systems as it is with signals and data originating outside the aircraft to use for cross check.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Debodine is 100% correct. In my in-flight incident with my altimeter, water in the static port causes the altimeter to get stuck at an altitude. Because it's rare to be stuck perfectly stable, I saw my altimeter fluctuate from a steady change during a climb to suddenly stopping and then jumping a few hundred feet. Clearly a failed instrument and obviously unreliable. Verified my standby altimeter was showing the same (they share the static port), and selected alternate static air supply. Problem went away.

However, if it stuck perfectly at one altitude and I wasn't paying attention, I might have kept climbing or even started descending without knowing it. I might see an airspeed that was then too high or too low for what I expected and start messing with the engine or pitch to try to "fix" it. This confusion could cost precious time while the airplane is slowly getting out of control. I would like to think I'm smart enough to avoid this but better pilots than myself have messed this one up.

Until they develop a closed loop system for the primary instruments (attitude, heading, airspeed, altimeter) the only thing I can do it keep training as much and as often as possible. Thankfully GPS has made things way easier and newer tech like synthetic vision is greatly simplifying instrument flying.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries https://www.facebook.com/AmericanConcrete/

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

GPS is still an afterthought in aircraft, I think.

GPS provides both groundspeed and an independent altitude. Ever since Air France, it struck me as odd that we're not able to built a better air speed sensor and/or figure out some way to use the GPS altitude and speed data to cross-check the air data.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

(OP)
Ian; Thanks for that description of sliding towards uncontrolled flight. Pretty subtle. Nasty! I know high performance airliners have a surprisingly small speed window at altitude for not stalling from the 447 disaster. I can see how in fairly short time you could exit that window, especially in a moonless night over an ocean.

For pitot speed instrument failures isn't GPS more than capable to get you air speed close enough to work. Oh, it's the fact that the air mass itself could be moving significantly isn't it?

Keith Cress
kcress - http://www.flaminsystems.com

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (smoked)

Oh, it's the fact that the air mass itself could be moving significantly isn't it?

That. And density.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

(OP)
Ah, that's right! A rather key aspect of lift and drag.

Thanks Mint.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Density tends to cancel itself out when the aircraft is in the air. And being in a moving mass of air is more a navigational issue than a flight performance issue until you get a sudden change in that movement which we term wind shear. Then the momentum of the aircraft comes into play and you can get suddenly relative drops or increases in airspeed. But steady state the aircraft doesn't know its in a moving mass of air.

Ground speed off the GPS is used on the flyby wire aircraft namely airbus but I have only ever flown one of them twice in the sim for an hour and haven't done the 5 weeks ground school conversion onto a airbus type so don't want to comment on how that works I just know on approach its involved somehow but quiet what it does I have no clue.

GPS quality is governed by a thing called RAIM the system automatically works out a quality factor and tells you when it drops below a certain value for a particular phase of flight or airspace. In the case of doing GPS approaches (RNP) we have indicators of what class of signal we are receiving and if its below whats mandated the box will refuse to give us the guidance to carry out the approach.

Now the thing that really kills lift is when the angle of attack of the aircraft exceeds the critical angle and the aircraft goes into a stall. There is a sudden drop in the coefficient of lift as the air flow breaks away from its lamina flow over the aerofoil and turbulent flow starts.

Now as such on civilian aircraft the only indication of angle of attack (AoA) is the attitude of the aircraft. The data is available because the stall protection system has usually 2 or more AoA vanes to get data from. And when it senses your near the limits it triggers various responses in the cockpit which are tactile(thing called a stick shaker) noise, and visual. If the AoA increases further it can then trigger a thing called stick push which applied nose down control input thus reducing the AoA.

Now what your actually doing in the cockpit when you fly a speed is set a AoA for what you want. For takeoff and landing its defined from the critical angle of attack and after departure you are setting the most efficient AoA from the lift drag curve. Its the same angle of attack its just the speed varies with weight. It is possible to have zero airspeed and not be at the critical angle of attack. But we don't do that sort of nonsense in transport aircraft.

No why do pilots fly airspeed not AoA…… historical and the whole training setup is geared towards nailing an airspeed.

I don't want to name my airline. The media dept does search the net for the airline name and its part of our contract that us pilots don't make statements on the company's behalf. Although nothing I have said is controversial they don't tell me how to fly a plane and I don't step on there toes.

Now I have to go throw an aircraft at the ground 4 times.

I will leave you with a training video which covers this subject.

https://youtu.be/WfNBmZy1Yuc?list=PLAjYL1_ZduxTtSk...

This series of training lectures are extremely good. Note the date they were made. These issues have been current for years and years. They are long every year we have 5 days of similar ground school looking at accident causes so we can hopefully trap the errors before they occur. IN the sim which occurs every 6 months for 2 day we recreate situations to see how to deal with them.

https://www.youtube.com/playlist?list=PLAjYL1_Zdux...

please note my comments above are extremely simplistic from both a pilots point of view and engineering. To behonest I really don't have time to provide a more comprehensive reply.







RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Contrast Air France 447 (crashed in the Atlantic) and US Airways Flight 1549 (landed in the Hudson).

An obvious and highly significant difference is that Capt Sullenberger concentrated on flying the airplane (while copilot Skiles was busy troubleshooting). According to the information I've seen, that division of responsibilities, ensuring that somebody was 'flying the plane', perhaps didn't occur on other incidents that ended badly.

In such emergencies, perhaps the displays on the left side of the cockpit should flash "Fly the plane!" in large letters.

Let the right seat do the system failure troubleshooting.

(Acknowledge in advance this is a vast oversimplification; it's intended to make the rather obvious point about CRM, user interfaces, distractions of too many error messages and Human Factors.)

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

That type of tunnel vision has been the root cause of more than a few accidents. Another, similar, cause is when the cockpit crew is afraid of the captain and doesn't articulate that there's a problem.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

GPS is an open loop system as well- but the inputs into any system processing GPS information are less corruptible than something like a pitot tube that can suffer from water or ice.

I can't imagine that GPS would ever be able to fully substitute for an on-aircraft, physical way of measuring airspeed. Just put an aircraft in the jet stream, and your ground speed and airspeed could be different by more than 100 kn; the position, velocity, etc of the jet stream aren't known precisely enough that you'd be able to use GPS to cancel out its effect all the time.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

I have to agree with jgKRI about GPS usage for airspeed not being viable. GPS can be used to precisely determine position, and from precise position to precise position, the velocity between the positions (ground speed), and I have even read of airborne experiments where four GPS receivers on an aircraft (nose, tail, left wingtip, right wingtip) did a pretty good job of determining roll, pitch and yaw. But to determine the airspeed within a moving mass of air that can't currently be accurately characterized with available technology, that remains a goal yet to be established and reached.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Why do you need airspeed?

There is age old system that pilots are taught.

Aviate navigate then communicate.

Btw that's my day just finished 280 pax moved. 10 cups of tea. 7 tons of fuels burnt. And the aircraft in the same state as when I signed for it this morning.



RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

(OP)

Quote:

cockpit crew is afraid of the captain
Tenerife captain of the Rhine.

I wonder if a simple heated probe being a mass-flow sensor coupled with a altimeter couldn't be used as a speed system. The barometer/altimeter to give air density the massflow with the density to give speed.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

smile you got where I am coming from. There are other ways of instrumenting aircraft to get what you need. But we are still using basically ww1 tech.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

But you also missed the time difference between my posts. I started in the dark and last landing was in the dark.


The dealing with issues at the beginning of the shift is shall we say different to the last sector of the day. The human limitations is also a major influence.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

" four GPS receivers on an aircraft (nose, tail, left wingtip, right wingtip) did a pretty good job of determining roll, pitch and yaw."

Using differential GPS (don't ask me) we no longer need conventional instruments (accelerometers, gyros, correvits) to do much of my vehicle dynamics work. But we can't measure windspeed using them!

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

that's called spurious stick shaker.

Normally when the stick shaker goes off it means your approaching the stall. So you do the stall recovery memory actions

Which are

1. reduce the pitch attitude.
2. roll wings level
3. power to max
4. once airspeed increase pitch for climb.
5. clean up
6. normal flight at safe altitude.

I might add this is the European recovery procedure. American pilots do it differently normally even though NASA and the FAA have told them to do it the same as us.

Spurious stick shaker we can kill with a single button push. But we are back to recognising that it is indeed spurious.

During departure your going to be at high power levels anyway and if you reduce the attitude to below the horizon the airspeed will within a couple of second exceed Vmo (max operating speed) and another alarm will start going off. At this point you have conflicting alarms one for high speed and one for low.

I have had this issue 3 times in my 8000 hours. Twice on the analog machine which has tabs on the wing which lift when the static point starts going under the foil. And once on a AoA vane stall system. Again for me the biggest problem was trying to convince my colleague we were no where near stalling.

Pitot tube blockage is another one which is interesting it makes the airspeed indicate that its rapidly increasing ie it turns the airspeed indicator into an altimeter. Increasing airspeed in the climb would normally lead to a pitch up to reduce it. If you pitch up to much you hit critical angle of attach and stall. Had that a couple of times on the analogue machine.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Alistair, from what I'm reading it sounds like the AOA discrepancy kicked on an automated nose-down trim, kind of like a stick pusher but more gradual and able to be overrode by the pilot either with yoke forces or via manually actuating the trim system. This kind of stall protection system is beyond my experience, though I do have training regarding runaway trim. Can you shed some light on what this article and the service bulletin from Boeing is discussing?

Quote (Alistair)

American pilots do it differently normally

We do? Your memory action procedure is the same as mine; though again I don't fly anything bigger than 4 seats so not sure if the airlines are doing anything different.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries https://www.facebook.com/AmericanConcrete/

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Yes there is a couple of areas which differ one is this stall recovery and the other upset recovery.

There is a fixation about not loosing altitude. So the power is applied while lowering the nose as a combined action. Then the wings levelled and then the pitch for climb. The way we are taught is almost a pause between each item. The problem with applying at the same time especially in swept wing jets is the pitch power couple. By putting the power in your getting a huge up couple which increases your AoA and can make maters worse. Then the fixation of not loosing altitude means that the pitch for climb occurs to abruptly which can and does frequently result in a secondary deeper stall. Most will try and power out which works on the stickshaker because its a incipient stall recovery and the plane isn't actually stalled yet. The only way to unstall a plane is to reduce the AoA. No difference between a C150 and a 747. if you have been taught the above method then its slowly working its way through.

The upset recovery is another issue, a lot of US pilots have been taught to lift the wing using rudder. This is fine if its a singular event ie you will get away with it even though there is more drag and the plane is completely out of balance. But if you have hit vortex with rapidly changing air flow it can result in a cyclic application of flight controls sometimes full deflection at way over rough airspeed. The classic example of this is AA587, after 5-6 cyclic applications of full rudder the tail failed.

Last BFR I did the FAA instructor really was not happy with me doing it the European way and that was 10 years ago. And some of our new pilots who did their initial training in the US are still coming into the sim with the American way of dealing with these situations so its still being taught.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

As I said previously I am not 737 rated but again we have a trim runaway procedure on all aircraft fitted with electric trim. Its one button/switch to kill the electrical trim system. The Boeings have a manual trim wheel as well and its scary loud and fast when it moves. The q400 if the trim system is active more than 5 seconds then an audible alarm sounds. And if ours fail we just have to hold it untrimmed which if its been allowed to go fully forward is a bit of sweat and swearing flaring.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (Alistair)

There is a fixation about not loosing altitude.

Ah, yep, I see the difference you're talking about and indeed I was trained the "American" way. When I did my instrument training there was some emphasis on unloading the wings first prior to rolling and recovering. We're still grilled about altitude loss, though. If we pause too much we fail the procedure due to altitude loss. I think part of it is primary training occurs in piston singles which are much more forgiving to recovery technique.

Quote (Alistair)

The upset recovery is another issue, a lot of US pilots have been taught to lift the wing using rudder.

I believe this has been changed; when I did my instrument training recently the upset recovery was taught to me as: unload the wings, level via ailerons and coordinated rudder, recover from the vertical upset, and set power to return to previous altitude. Still, I imagine many older instructors are teaching the older methods.

Quote (Alistair)

trim runaway procedure on all aircraft fitted with electric trim

In the G1000 Cessna I fly the procedure is identical. Holding A/P disc kills electric trim, if trim is in motion for more than a few seconds we get an audible warning, and if it gets out of hand we can manually override the A/P clutches with a complimentary arm workout. Funny how the technically advanced GA aircraft are becoming more and more like a single-pilot jet in terms of procedures and avionics.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries https://www.facebook.com/AmericanConcrete/

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

to be honest mate I am legal to fly this. And your G1000 is fancier than the Q400



And this

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

opps chose the wrong picture of the Jetstream cockpit its has a FMS and auto pilot the ones I fly have no autopilot and this is the gps.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Heh, the G1000 makes single pilot IFR so simple. I occasionally go up and do some IFR work in an old C152 just to make sure I can still fly without a computer doing 90% of the work for me. Not going to be one of those pilots who can only follow the magenta line.

Anyway, back to the topic; what I'm reading some component was replaced by the airline prior to the fatal flight. I'm sure the accident chain will include all parties but this is seeming more and more like a Boeing design issue. Too soon to make that judgement you think?

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries https://www.facebook.com/AmericanConcrete/

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

For those playing at home; here's the cockpit of the G1000 system Alstair and I are talking about:



Modern single engine trainer aircraft these days often have more advanced avionics than many of the older airline fleets. Nothing wrong with the older tech of course and the cost to update doesn't make sense; still amusing though.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries https://www.facebook.com/AmericanConcrete/

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Speed Trim SystemThe Speed Trim System (STS) is a speed stability augmentation system designed to improve flight characteristics during operations with a low gross weight, aft center of gravity and high thrust when the autopilot is not engaged. The purpose of the STS is to return the airplane to a trimmed speed by commanding the stabilizer in a direction opposite the speed change. The STS monitors inputs of stabilizer position, thrust lever position, airspeed and vertical speed and then trims the stabilizer using the autopilot stabilizer trim. As the airplane speed increases or decreases from the trimmed speed, the stabilizer is commanded in the direction to return the airplane to the trimmed speed. This increases control column forces to force the airplane to return to the trimmed speed. As the airplane returns to the trimmed speed, the STS commanded stabilizer movement is removed.

STS operates most frequently during takeoffs, climb and go-arounds. Conditions for speed trim operation are listed below:•STS Mach gain is fully enabled between 100 KIAS and Mach 0.60 with a fadeout to zero by Mach 0.68
•10 seconds after takeoff
•5 seconds following release of trim switches
•Autopilot not engaged
•Sensing of trim requirement

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Found that on the system in question although quiet how that links into the AoA system is obviously a need to know system knowledge.

And way way to soon to make anything other than interest comments as we have been doing on the general systems how they work and human performance issues.

One of the reason why I registered was partly to do with my background as an engineer but also because with hindsight I realised that my engineering training was really quiet poor at highlight the human interaction and reaction aspects of the projects I was involved with. And from my lurking particularly this forum section I saw what a great bunch of thinking and opened minded people were participating.

You just have to look at that ergonomic heap of shite which is the Jetstream (35 year old design) and compare it with the Q400 which is 15 years old to see how things have progressed. But have they progressed too far? Is there too much data being pushed towards the user. This has implications in several applications I have "gone back" to an old haunt in Nuclear to teach Crew resource management and Threat Error Management (TEM), also I have taught medics as well and got them to use checklists.

As engineers its something to think about.

I am opened minded if its a design issue or human factors/training. You have to remember that the 737 would not pass current certification standards if it was a green fields design. Its been stretched digitised and tinkered with all on the back of a 1960's design and the certification standards of the day. Similar to the DXB EK521k which is now going through the courts claiming design failure. As a punter involved yes have your day in court.... but honestly as a pilot you don't just press a button and expect the machine to do as you expect. You verify its the correct button, then you press it and then you verify again that its had the effect you want. You press a button wanting toga power and you don't see the needles rising and you don't feel a kick in the pants as the power winds up... you bloody well shove the power levers forward and pitch the nose to the required attitude.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

(OP)
The PhyOrg article states differing "AoA of 20°".

That seems huge to me. What are the typical values of AoA seen in airliner operations?

Keith Cress
kcress - http://www.flaminsystems.com

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

yes 0 to about 15 degrees anything more than that and your into critical angle of attack which means the stall system is triggered.

I maybe guilty of presuming that people know what the critical angle of attack is and its approximate value in my posts... I do apologise.

As soon as I saw 20 deg split I presumed the stick shaker system was triggered.

0 is extremely rare and would be extremely uncomfortable to the pax. The wing incidence which is shall we say welded is about 1-2 degs and we would normally cruise with 1-2 deg nose pitch up giving about 3 deg in the cruise but this does depend on what cost index we are using and what the "sweet" AoA is for coefficient of lift and Coefficient of Drag.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

If pitot tubes keep causing problems (system failures, ice build-up, water, mud dauber wasps, masking tape leftover from painting....the list goes on and on), then it may be time to consider back-up systems, based on an alternate technology, with a well-designed method of combining the information (Kalman filter concept).

Quora says, "Hot wire anemometers arranged in a circular pattern can determine both wind speed and direction. Another method is using ultrasonic based sensors." These used to measure wind.

Lasers are also mentioned, in terms of tracking microscopic airborne particles.

And with GPS as another input for our purposes.

Strings attached to the windscreen and sidescreens like gliders?

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

0 is extremely rare and would be extremely uncomfortable to the pax really, really fun!

But, yes, most (all?) planes cruise with a few degrees of AoA. Bernoulli and Newton generally both are at work to make a wing fly.

Quote (Alistair)

cost index we are using and what the "sweet" AoA is for coefficient of lift and Coefficient of Drag.

Oh, do expand on this. Is AoA how you target efficiency for cruise flight? (dragging us off topic, sorry)

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries https://www.facebook.com/AmericanConcrete/

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (VE1BLL)

then it may be time to consider back-up systems

You're not wrong but how would any of these systems not also be susceptible to the same failures as a pitot-static system?

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries https://www.facebook.com/AmericanConcrete/

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

20 degree differential between two AoA data streams is huge.

There's no exact numbers- optimal angle of attack for an airfoil in any particular steady-state flight condition depends on aircraft weight/CG position, mach number, density altitude, and position on the wing. Position on the wing is interesting to keep in mind, because most aircraft wings are swept combinations of several, sometimes many, individual foil shapes and there is typically twist in the chord angle between the root and the tip of the wing; so the 'true' AOA is different at any given point on the wing. The reason for the airfoil twist in the wing is actually to control where stall conditions first arise on the wing to make the stall more progressive and easier to control/recover.

Anyway. Most conventional airfoil shapes will have a stall angle between 15 and 20 degrees, and actual operating aoa will be much lower, say 2-4 degrees.

So yeah, having two aoa streams, one telling you that the aoa is 2 degrees and the other saying it's 22 degrees is potentially really, really bad.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

to be honest I reckon aircraft fly because of newton but are controlled because of Bernoulli.

If you have a flat piece of wood at an angle to an airflow it will produce lift and give a force vector.

We don't get AoA in the cockpit but most performance stuff is related to AoA and where you are in the drag curve Vy will give you the best performance because it gives you the least drag. But there are other financial cost and because the increase in drag is not linear then they adjust the cost index to take into account the fuel price.

Because we can't set a AoA we get an app or pages of performance data which links weight to power requirements which is a round about way leads to a AoA being set. There is another fudge factor built in which takes into account head and tail winds so we fly faster in a head wind and slower in a tail wind which factors in the maint costs per hour of operation. Also the air temp changes the settings and the fuel burn. IN the jets with auto throttles its all done by the Flight management system. Turboprop drivers have to do it manually we look at the temp, head/tail wind, weight and altitude and put them into an app on a Ipad and then it spits out a torque setting. We set it and order a cup of tea. last flight of the day we may choose to ignore the app especially if out mates are flying and its a race to get home first.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (TehME)

...susceptible to the same failures as a pitot-static system?

The goal would be to reduce the odds, so that Airspeed Indicator issues might be persuaded to move way down the list.

Commonality can allow common failure modes, in spite of redundancy. e.g. AF447.

(By way of counter-example: If I recall correctly, the Space Shuttle famously had intentionally diverse flight control computers. Triple redundant, but all three different. Different hardware and different software.)

As has been noted, Human Factors is a major contributing factor with these incidents. So how backups are all integrated and presented seems like the difficult aspect. Multiple diverse sensors is the relatively easier design aspect.

The complex interactions between bad or confusing data and the pilots, leading to an otherwise functional aircraft to crash, seems to be a recurring theme. Engineering or designing out these sorts of issues seems like an issue worth addressing.

I'm not an SME on this topic. These are just opinions based on what I've seen or read.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

The space shuttle even with its redundancy still ended up with instrument failures and some hairy landings.

All the pilots on the stick were test pilots who have super human data processing ability's. They still screwed it up occasionally.

And as the poster above says the changing of the design and the presentation of data is constantly evolving.

In the next 12 months I will be getting trained up on this aircraft.



Still fly's the same as the Jetstream. No paper no checklists, only memory item is to put your o2 mask on if there is smoke.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Looks like an A350. What's the giant red button do?

Has Airbus finally made it so you have some feedback on what each side stick is doing? (i.e. Airfrance crash)

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries https://www.facebook.com/AmericanConcrete/

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

That's the eject button, obviously

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

It is an airbus but a Canadian one not a French one winky smile

I haven't got a clue what the big red button does. I suspect its a flight test aircraft. They are set up a bit weird because they have huge water tanks in the back and they can pump between them to do the CofG testing and variable weight for the envelope testing.

Always gets the chemtrail lot excited when they see funny buttons and water tanks in the back. closely followed by the flat earth lot asking if the water is flat or at an angle.

I don't remember seeing it on our fleet the couple of times I have jumpseated.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (jgKRI)

That's the eject button, obviously
I think it's an emergency stop.

Brad Waybright

It's all okay as long as it's okay.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Strikes me that the big red buttons are associated with the special red panel in the center console.
Shifting water back/forward, with a valve Open/Close/Fail annunciator on the red panel... perhaps a "dump" on the panic button? Just guessing.
Back in the day, Canadair (predecessor to Bombardier) had a test flight crash, due to CG too far aft.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

That makes a lot of sense Spar.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries https://www.facebook.com/AmericanConcrete/

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

The word out from Boeing to RTFM was real subtle.
Why they were still flying a plane with wonky sensors, well it is Lion.
In that part of the world there are not a lot of good options.
I flew Garuda once, it was an old 737 that they couldn't pressurize because of gaps in the skin panels.
It didn't matter we were island hopping, about 15 min in the air and never above 3,000ft.
The livestock on the plane was very interesting.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Aft CofG is a killer, forward C of G is just a work out of your arms and a rather firm arrival.

On the Q400 None public transport we get a additional lump of performance graph to play with in the forward part. Rear is a hard limit and don't screw around with it. Thankfully its extremely hard to get into even with the pax cabin empty and the rear hold full. You would have to fill the rear hold and only seats behind the wing to get near it.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Isn't that big red knob the tow rope release?

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

I was on a 45 minute flight on a King Air that had the CoG so far back that we were sitting on the tail prop with the nose in the air.
The pilot and co-pilot boarded and climbed uphill to their seats. As they were strapping in the nose slowly came down and the nose wheel bounced once on the ground. I guess three point contact meant good to go.
For 45 minutes we were at such an extreme AoA that I kept thinking;
"If the engines fail, we are going to slide backwards down into the ocean."
As you may have deduced, we made it.
Some of the King Airs had a radar set mounted low down on the center of the dash.
One plane had a full size colour picture of a radar set glued in the place where the radar set would normally be mounted.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]


Emergency AD Issued On B737 Max






The FAA has issued an Emergency Airworthiness Directive (PDF) that directs the owners of all Boeing 737 Max aircraft to amend their operating manuals, to avoid a control problem like the one that apparently caused the fatal crash of a Max 8 last week. “Possible erroneous angle-of-attack inputs on Boeing 737 Max aircraft … can potentially make the horizontal stabilizers repeatedly pitch the nose of the airplane downward, making the aircraft difficult to control," the FAA says in an emergency AD dated Nov. 7. The airplanes are not grounded, and the owners have three days to comply with the AD, which requires a revision to the airplane flight manual.
“This emergency AD was prompted by analysis performed by the manufacturer showing that if an erroneously high single angle of attack (AOA) sensor input is received by the flight control system, there is a potential for repeated nose-down trim commands of the horizontal stabilizer,” the AD reads. “This condition, if not addressed, could cause the flight crew to have difficulty controlling the airplane, and lead to excessive nose-down attitude, significant altitude loss, and possible impact with terrain.” The AD requires revising certificate limitations and operating procedures to provide the flight crew with runaway horizontal stabilizer trim procedures to follow under certain conditions.
B.E.

You are judged not by what you know, but by what you can do.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

How exactly the LionAir 737's AP could have gotten confused is not yet clear to me, even with the text of the AD to refer to. It seems a declaration that the AP system's functional hazard analysis has been found to be invalid, or relied on a backup source that doesn't do what it's supposed to. The AD says nothing about the configuration of the AP system, as if one faulty sensor should be expected to provoke a wild ride. It absolutely should not. The text of the AD makes mockery of a reliability requirement that has been standard practice in flight system design since the 1960's.

Part of the functional hazard analysis (FHA) for any critical flight system is the need to identify faulty readings, and disregard them. The resolutions become built into the design and programming of the system.

The Autopilot system must be programmed to compare, select, filter, or vote in some way that deals with bad sensors, otherwise the moment your anti-icing system fails you go into a spin. All of the sensors are backed up with at least a duplicate, and wherever possible a completely alternative source that can reconstruct the same information. AoA can be measured directly from AoA sensors (the 737 Max is typical, has two of these, one on each side of the cockpit) and a couple of inertial navigation units (INU) within (probably) more than one attitude and heading reference systems (AHRS). There may be other ways; I'm not a sparky. I do not know what system is on board the 737 max, so I do not know what it actually uses for backup data. But the requirements of FAR 25.1309 speak for themselves, and no single failure may pose a hazard to the aircraft.

I would like to know if sensor de-icing was turned off, or malfunctioning at the time. The flight crew would be aware of either conditions, if they were happening. Since the text of the AD doesn't demand examination of the de-ice, or admonish pilots to keep it turned on, this may have been checked already, and ruled out.

This AD sheds no light on what happened, to me. Raises more questions than it answers.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Could differential information collected from GPS receivers in the nose and the tail provide attitude information and/or AoA information?
Maybe not exact, but surely enough to identify a 20 degree error.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (STF)

...sensor de-icing was turned off, or malfunctioning...

Can icing occur 5000 feet over Indonesia? Also, within such a few minutes?

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

GPS is too slow (IIRC) to act as an attitude reference.

With a ground temperature of ~27C, and a dew point ~24C, you are right to be skeptical of icing. However, the atmosphere does not always obey the standard temperature lapse rate.
Since I haven't seen anything yet explicitly ruling out this problem, it remains "on the board" despite the low probability. Especially since it was a contributing factor in the AF447 crash, which bears some similarities.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

"Could differential information collected from GPS receivers in the nose and the tail provide attitude information and/or AoA information?
Maybe not exact, but surely enough to identify a 20 degree error."

We use GPS sensors at the front and back of the car to measure yaw velocity pitch and accelerations on cars for vehicle dynamics work.

These have replaced conventional accelerometers and gyroscopes so far as we're concerned. Bandwidth >10Hz

Differential GPS should be able to measure nose to tail pitch distance to within 800mm, which, unless you are flying very short aeroplanes, would comfortably indicate to a degree or so.

Not too sure where SparWeb is coming from on this.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

It was phrased as a guess, about the GPS for attitude. If you can get 10Hz and <1m resolution from a GPS board then sure, it can do that if you want it to. And want to add antennas to the tail. May not be necessary if you already have multiple AHRS units with IMU in the aircraft, but a backup to a backup... I didn't mean to get drawn into a comparison of IMU / GPS resolution and data rates. This is far from my specialty, so if you can prove me wrong, touché.

I did feel comfortable asking questions about the seeming lack of redundancy in the AP system. This is more in my wheelhouse. Something there doesn't add up. One faulty AoA sensor should not render the aircraft difficult to control or uncontrollable. The message in the AD (see attached) speaks of a very difficult condition to recover from:

Quote (FAA)

Runaway Stabilizer
Disengage autopilot and control airplane pitch attitude with control column
and main electric trim as required. If relaxing the column causes the trim to
move, set stabilizer trim switches to CUTOUT. If runaway continues, hold
the stabilizer trim wheel against rotation and trim the airplane manually.
Note: The 737-8/-9 uses a Flight Control Computer command of pitch
trim to improve longitudinal handling characteristics. In the event of
erroneous Angle of Attack (AOA) input, the pitch trim system can trim
the stabilizer nose down in increments lasting up to 10 seconds.
In the event an uncommanded nose down stabilizer trim is experienced
on the 737-8/-9, in conjunction with one or more of the indications or
effects listed below, do the existing AFM Runaway Stabilizer
procedure above, ensuring that the STAB TRIM CUTOUT switches
are set to CUTOUT and stay in the CUTOUT position for the
remainder of the flight.
An erroneous AOA input can cause some or all of the following
indications and effects:
• Continuous or intermittent stick shaker on the affected side only.
• Minimum speed bar (red and black) on the affected side only.
• Increasing nose down control forces.
• IAS DISAGREE alert.
• ALT DISAGREE alert.
• AOA DISAGREE alert (if the option is installed).
• FEEL DIFF PRESS light.
• Autopilot may disengage.
• Inability to engage autopilot.
Initially, higher control forces may be needed to overcome any
stabilizer nose down trim already applied. Electric stabilizer trim can be
used to neutralize control column pitch forces before moving the STAB
TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be
used before and after the STAB TRIM CUTOUT switches are moved
to CUTOUT.

The previous AFM instructions were a common "abnormal procedure" for when the elevator trim system suffers a runaway. That kind of procedure is known to pilots. Even light aircraft flight manuals will advise how to respond to failure of the trim system.

This new procedure is more dire, describing the crew's response to "higher control forces" and "relaxing the column causes the trim to move". Makes it sound like an AP gone crazy, not a trim runaway.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

The trick is to use several GPS at the extremity of the vehicle. Most of the noise in a GPS output is due to atmospherics, so if you have more than one they seem the same errors, and so when you subtract the outputs (hence the name differential GPS) the noise disappears.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

this is a bit of a funny one because the trim system that's effected is only functional when the plane is being flown manually.

Quote:

• Continuous or intermittent stick shaker on the affected side only.
• Minimum speed bar (red and black) on the affected side only.
• Increasing nose down control forces.
• IAS DISAGREE alert.
• ALT DISAGREE alert.
• AOA DISAGREE alert (if the option is installed).
• FEEL DIFF PRESS light.
• Autopilot may disengage.
• Inability to engage autopilot.

Now thats some list of items to go wrong and apart from the AoA mismatch possibly Feel diff none of them we would immediately associate with having problems with the Angle of Attack sensor.

With my engineers hat on instead of pilots if the AoA data is getting linked into so many systems i would say it needs to have a third backup vane to allow 2 out of three agreeing for fault tolerance just like we do with the other primary data sources.


RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (GregLocock)

The trick is to use several GPS at the extremity of the vehicle. Most of the noise in a GPS output is due to atmospherics, so if you have more than one they seem the same errors, and so when you subtract the outputs (hence the name differential GPS) the noise disappears.

I think that some of the issues here regarding the viability of GPS for use in determining the real-time positioning of aircraft and their orientation are due to the conflation of a few different concepts. Not being an expert, I will be speaking in generalities. But I think I have some idea of what is happening here.

The first is your explanation of the name differential GPS. It's true that comparing the difference between local celestial GPS outputs will be more accurate than looking at a single celestial signal, but only marginally so. That's comparing the absolute location (where am in the world) vs. the relative accuracy (where am I relative to this other local sensor experience the same atmospheric interference).

Differential GPS relies on terrestrial base stations transmitting from fixed, precisely-known locations to broadcast a signal correction to the rovers allowing for very precise real-time location. These fixed terrestrial base stations need to be located within several miles of the rovers for the system to function properly.

Am I correct in my assumption that where you are using the differential GPS to measure vehicle dynamics is at a fixed location like a test track and not out and about anywhere in the world at any given time?

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Aircraft don't use dgps. We use the SBAS system.

Galileo if it ever comes online will also give much better resolution.

Even dgps is a bit pants at vertical position.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

While GPS attitude/heading sensors use the differential signals and phase between antennas to determine angles, they are not technically what is(was) called dGPS. dGPS traditionally refers to using a receiver with surveyed, absolute, GPS location with the same receiving environment to "correct" the GPS at an unknown location. This removes the atmospherics as well as the inherent errors in the GPS satellite outputs to achieve, in the best cases, sub-centimeter positional accuracies.

An attitude GPS with 10-m antenna separation can achieve heading accuracies better than 0.02° rms, which is better than the heading performance of an eTalin from Honeywell. However, during a bad enough war, the US GPS likely will turn back on its Selective Availability, which would possibly cripple a GPS-based attitude/heading sensor. However, modern GPS receivers can receive at least the GLONASS signals, and may still have decent performance.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

It was my understanding that the various flavours of GPS reception based on differential signals were developed to cancel out the effects of selective availability.

There was an urban legend concerning Selective Availability during the Gulf war.
Legend had it that during the Gulf war, the army had a demand for quantities of military grade GPS receivers that could not be met quickly enough. (Apparently there is second set of GPS signals that is available only to the US military).
According to the legend, selective availability was turned off so that civilian GPS receivers could be used by the US military.
Some of us felt that the GPS accuracy was improved during and after the war.
Is there any correlation for this legend?

My concern is that the GPS system may be turned off completely during a war, or at least the civilian service.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

The sa has been turned off for years.

And it is that easy to jam GPS that they have said they won't turn it on again. With Galileo transmitting low Res as well these days it's pretty pointless turning it on again.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

All this talk of using GPS for attitude reference is getting off topic. I am duly impressed by growing capabilities of GPS. It is not used for this function in commercial aircraft. GPS has other functions in commercial aircraft, most especially as a navigation reference. You can even couple your approach to runway landing to a suitable GPS reference. However, attitude is not navigation. Nose pitch up and pitch down is attitude, not navigation.

This is what commercial aircraft use for AHRS (Attitude & Heading Reference System).
Collins
Universal
Honeywell

They contain MEMS gyros. Lots of them. There is no co-ax connector on these boxes. They don't use GPS.

With this context clarified, my question bcomes "How did the autopilot system let the airspeed sensors out-vote the AHRS sensors?"

Now that I'm on this rant, I would be remiss if I didn't spill some more acronyms, such as Air Data and Inertial Reference Unit (ADIRU) and Standby Attitude and Air Data Reference Unit (SAARU), which are similar to the AHRS, except they actually DO HAVE airspeed data inputs. Each of these also depend on inertial references for attitude. The 737 MAX may have multiples or none, depending on the system design. I don't have a 737 MAX Flight Crew Operation Manual here, so I can't tell you exactly which boxes it uses. If it does have these, then inside these specific boxes is an algorithm that evaluates the integrity of all data sources and chooses the best for the attitude and condition of the aircraft. I really want to know if something is going wrong inside these boxes, causing the confusion in the flight director system, because that confusion is supposed to be designed out of them. At a very fundamental level, the design goal in these systems is to minimize this specific hazard.

Here's a summary of the Boeing 777's Fly-By-Wire System for reference. The new 737-Max could be similar.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

just been speaking to a mate that's done the differences training on it.

Apparently there was no mention of this trimming system feature during the training.

BTW this system is not linked to the Autopilot system its linked to the trim system with an input from the stall protection system apparently. They are getting almost daily updates on the subject. Every time they check in there is updates.

They suspect there will be an airworthiness directive with a mod on the subject.

The 737 max is not fly by wire flight controls. It has fly by wire spoilers and bleed air.

the triple is digital flight controls. ie no direct control runs to the flight controls.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]


The latest from the NY Times:

Link

Looks like the pilots fought the MCAS until the end.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

(OP)
Very enlightening.
Thanks.

Read a couple of the reader comments NYT picks too.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (NY Times)

Information provided to American Airlines from Boeing since the crash, Captain Tajer said, “specifically says that pulling back on the control column in the Max will not stop the runaway if M.C.A.S. is triggered. That is an important difference to know.”

That sinking feeling...

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Does anyone remember the joke from the early days of automation?
As an aircraft is taking off an announcement is made over the PA system;
"This aircraft is equipped with the latest, most advanced auto-pilot.
The plane is now being flown automatically.
You are perfectly safe.
Nothing can go wrong..can go wrong..can go wrong..can go wrong..can go wrong..can go wrong..can go wrong.."

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

There is a fair bit of information and discussion out there if you go searching. A few pilot forums too but they aren't readily open to public viewing.
Just one source:
https://www.airliners.net/forum/viewtopic.php?f=3&...

This is probably one on the better media articles:
https://www.seattletimes.com/business/boeing-aeros...



Quote (SEATTLETIMES)

The data points to three factors that seem to have contributed to the disaster:

A potential design flaw in Boeing’s new anti-stall addition to the MAX’s flight-control system and a lack of communication to airlines about the system.
The baffling failure of the Lion Air pilots to recognize what was happening and execute a standard procedure to shut off the faulty system.
And a Lion Air maintenance shortfall that allowed the plane to fly repeatedly without fixing the key sensor that was feeding false information to the flight computer on previous flights.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

As with all aviation accidents, there will be a string of seemingly unrelated causes that contributed to this crash, such as the flight system automation, training, and probable faulty hardware, but it seems now that the predominant cause will be attributed to allowing this airplane to fly in the first place. I read somewhere that troubles with the AOA sensors had been reported for 5 days preceding the crash. I can't find the source now and that may not be true. Regardless, it seems that the previous flight was only able to avoid disaster through some set of knowledge and skill that the pilots of the accident flight lacked. I'm sure that the real legacy of this will be settling lawsuits for years to come.

Brad Waybright

It's all okay as long as it's okay.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

A switch to turn off a malfunctioning system, that repeatedly turns itself back on may not be the best idea.
It may be a great novelty, but not the way to fly an airplane.
Link
I can imagine the pilots confusion turning to frustration and then to panic as the yoke switch repeatedly turned itself back on.
Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Plenty of fault to go around but why didn't the pilots return to the airport and land the thing? The reports say it was malfunctioning from the moment they took off. Seems like a culture to just keep flying no mater what is wrong. Remind me to never fly Lion Air.

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RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Its easier to say than to actually do... And when you have control issues you keep the wings level because the stall speed goes up in a bank and also you loose climb performance.

This system is only used during manual flight, it gets turned off when the auto pilot is engaged.

And a lot of pilots wouldn't step foot on quiet a few carriers.... including some carriers you would be surprised at that are western and national carriers.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Taking Frontier in a few weeks to visit the in-laws. I'd say wish me luck but don't worry; I'll make sure to knock on the pilots door to wake them up when it's time to land. bigglasses

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL)
American Concrete Industries https://americanconcrete.com/

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Don't go near the door please, its classed as an attempt to enter the cockpit. And that's shite loads of paperwork.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Man, I miss the days when pilots could occasionally ride jumpseat with the crew...

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL)
American Concrete Industries https://americanconcrete.com/

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

We miss it as well, nothing better than having people on the jumpseat for a sector. Gives us someone different to talk to. And the whole system for going for a pee is a complete pain.

We can take certain individuals on the jumpseat with a relatively easy system (one phone call ) to get approval. And the boss is all in favour of letting known suitably aged kids in the cockpit if they want.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (waross)

A switch to turn off a malfunctioning system, that repeatedly turns itself back on may not be the best idea.

That is an interesting problem. How do you design a system that fills in the blanks of human perception, can be disabled in case of malfunction, but cannot be too easily disabled or ignored in case the pilots are mistaken in their belief that the system is malfunctioning, etc. It seems like there was a procedure for disabling the system but it required one extra step that the pilots were not aware of.

I'm probably mixing up my incidents but I think it was the Air France flight out of Rio where sensors were icing up in dark clouds, pilot was pushing nose down to avoid stall and pick up airspeed while co-pilot was secretly holding the stick back to get above weather and flew a perfectly good aircraft into the Atlantic because they did not have confidence/agreement in their airspeed and stall indicators.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (dgallup)

Plenty of fault to go around but why didn't the pilots return to the airport and land the thing?

I'm not sure how going nose down into the tarmac would be preferable to nosing down into the water.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

(OP)
waross; I believe the ultimate solution was not a 'cancel' switch but the circuit breaker. The system was also disabled by setting any flaps and they actually guessed that using it as a method a few times but for some reason eventually gave up on that avenue, which would've gotten them back on the ground. (That's on - not in.)

Keith Cress
kcress - http://www.flaminsystems.com

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (stevengal)

I'm not sure how going nose down into the tarmac would be preferable to nosing down into the water.
They flew it for 12 minutes before the crash, most of the time going up or maintaining altitude. If I were fighting a piece of out of control equipment, I would want to get it to some safe position and shut down, not just keep on fighting it forever.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

I am sure they did as well, better to be on the ground wishing you were flying than in the air wishing you weren't.

There should be no requirement in this day and age for a pilot to have to hunt for a Cb to to kill a system.


I have a panel with 25 by 30 grid on it of CB next to my seat. And the FO's have the same.


The should stop any more interations of the 737 using the old certification grandfather rights which is based on a 1960's design.

New certification to modern standards not just fundging things so they don't have to comply with modern standards or do a full certification testing program.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (Alistair_Heaton)

using the old certification grandfather rights

That's the "changed product rule". It gives a lot of leeway to make modifications and upgrades.
If you want to dig deep, check out the link below and follow the rabbit hole down to Appendix page A-48 (just for one example; there are more).
AC 21.101-1B

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

it gives way to much leeway for piss taking. I am more than aware of what goes on stretching and modifying.

its started out as a 80 seater 1000 NM airliner.

The 737 max is 230 pax and 3300 NM



they are all at it as well.



RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

In my wife's new car when I push the off button on the radio, it gets quiet and the driver information display shows a message;
"SOUND MUTED, PUSH AGAIN TO TURN OFF"
That's a lot more effective than an e-mail or a short paragraph in the owner's manual.
I wonder if a similar system could be used to turn off a malfunctioning system?
I can't understand how a system with the capability to fly an aircraft into the ground can be designed and installed without any self checks for bad inputs.
Money I guess.
I have no sympathy for Boeing whatsoever.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Generally, there isn't anywhere to put a "friendly message" like that in a down-to-business aircraft flight deck.
It reminds me of Arthur, arriving on the Heart of Gold. He pushes a button at random, and a sign lights up, saying "Please to not push this button again". (You either get the reference or you don't.)

Since pilots train using checklists, flight manuals, and operating procedures, you can expect most pilots to be familiar with nearly all of the switches and their functions before crewing with passengers. When things go wrong, or things start working in strange ways that the pilots didn't train for, that's when the experience and personality make the difference. There have been pilots (I can name a few such crashes) unable to diagnose a problem that another pilot would have recognized and adapted to quickly.

I downloaded the preliminary report, and I've studied the sequence of events plots. I personally think that the faults happening were strange in the extreme, and it would be unfair to expect "any" crew to handle this well, or succeed in troubleshooting it, even if I also believe that this crew had enough time to figure out that the problem was not going away, threatening them, and should have turned back. The runaway trim problem (or so it would have appeared to the crew) was preventing them from climbing, thereby eliminating any margin of altitude to deal with any OTHER problem that might come. With all the trouble they'd had with previous flights, they should have expected a problem #2 to come. Flight crews should be able to distinguish between problems that go away when dealt with, and problems persist to erode safety margins leaving no room to handle any other distraction. This is basic flight planning and crew resource management stuff.

So here we have the "swiss cheese" model of failure prevention. The possible barriers were:
1) system design to prevent single causes leading to catastrophes,
2) maintenance procedures to test & assure equipment functions when replaced,
3) flight procedures to follow when equipment malfunctions,
4) training to teach crews the procedure to follow and to build experience and judgement.

Holes formed in all of these barriers, letting this fault through.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Agree with spar.

In general crew can deal with 2 issues at the same time, as soon as three crop up either interrelated or separate then the chances of a successful landing become greatly reduce and also luck starts playing a part.

Electrical faults tend to give an over abundance of lights to sort out and knowing which one to deal with first out of the 20-30 lights that are active can be a challenge. Its not unknown for situation that requires a generator to be taken off line and bus tie opened for a crew to head off in the wrong direction and end up on emergency instruments and an engine shut down. When the correct solution would have only resulted in the galley power being cut and no hot tea for the remaining flight without diversion.


Quote:

When things go wrong, or things start working in strange ways that the pilots didn't train for, that's when the experience and personality make the difference. There have been pilots (I can name a few such crashes) unable to diagnose a problem that another pilot would have recognized and adapted to quickly.

This is very correct. And I also agree that your average crew which ever nationality they are or carrier would be emptying their bag of luck rapidly during this type of failure. Its the sort of thing the sim examiners throw at you when they have decided that your checks are getting too easy. Murder the FO and start failing systems until your eventually over loaded. I can tell you hand flying the aircraft single engine while manually pumping down the gear is hard work.... and you just know the weather is going to go down as soon as you have committed to putting the drag out with the gear with no way of getting it up so you won;t have enough fuel to get to your diversion.






RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

I assume there is an alarm or message to the crew that there is a discrepancy between primary and backup sensors. I set up controls this way when 2 sensors for the same parameter are available. Maybe it's an oversimplification of the actual subsystem, but it seems that this should alert the pilots that a sensor is malfunctioning and then they should have the option to select the one which seems to be correct.

Brad Waybright

It's all okay as long as it's okay.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Not that I have heard of with the AoA sensor...





That's what I have for sensor errors. Your not given AoA data in the cockpit as a raw value. You can see it changing by the red stall indicator at the bottom of the speed tape so I suppose if the pilots compared the red zone on the speed tapes you could spot a problem. But its not something you are currently trained to do. To be honest I wouldn't like to say how many pilots might not make the link between the red tape and it indicating angle of attack. And mid struggle trying to keep the nose up it would be hard. Must admit I give the AoA vanes a waggle every turn round and only once found something not feeling right, it was swapped out before the next flight. But a lot of aircraft you can't reach them from the ground so would require a cherry picker or set of steps.

Was thinking today about it. Maybe a pair of backup AoA vanes up on the fin would work but they would catch vortex off the flaps possibly.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

I never realized that these AoA things were these little wing like things sticking outside of the aircraft - the NYT has a good description of them https://www.nytimes.com/2018/11/09/world/asia/air-...

From the traces supplied it almost looks like the instruments are being read differently, i.e. the 0 reading on one is somehow seen as +20 by the other. That implies somewhere the setting of the readings by the system wasn't properly zeroed?

Are these things handed somehow? or are there two one above the other on a 737? I can't imagine that they aren't somehow physically fixed in the same way so that zero degrees is the same and you can't rotate the thing one bolt hole by accident? Could you?

This photo purports to be two B737 AoA sensors and I can't see any fitting which wouldn't stop it being rotated incorrectly.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (LittleInch)

This photo purports to be two B737 AoA sensors and I can't see any fitting which wouldn't stop it being rotated incorrectly.

I doubt very highly that they need mechanical clocking.

Dollars to doughnuts, that body contains an incremental rotary encoder which is re-zeroed whenever the system is powered up.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Are the two AoA sensors considered to be redundant, or do they somehow work together in concert? If redundant, it seems prudent that there should be an alarm to report a discrepancy or 'mismatch', as it were.

Brad Waybright

It's all okay as long as it's okay.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

you can see the circuit diagram on the side of it. Its just a potentiometer.

They usually have a couple of bolts out of phase with the rest and lugs at funny angles so they can only be fitted the right way and on the correct side.

Plus also there will be a part number check with the old one when its replaced.

And they don't sit at zero when the aircraft is powered up for a bite check. They can be at any angle mainly due to local wind conditions. Still winds they will at the bottom of travel and 40 knts of wind on the nose and they will have lifted.

Limit for taxing and starting engines is usually in the 65knt region with a Vr (takeoff speed) in the 120-130 knt region depending on weight.


As i have said before its 1960's tech.



RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (Alistair Heaton)

you can see the circuit diagram on the side of it. Its just a potentiometer.
Actually, I believe it is a resolver. Either way, whether left or right, swapping polarity of supply power would provide duplicate signals from each side, whether degrees down, degrees up, or neutral would be the same so the sensors would be identical.

Brad Waybright

It's all okay as long as it's okay.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Would that work with a frequency wild AC supply?



RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (SparWeb)

Generally, there isn't anywhere to put a "friendly message" like that in a down-to-business aircraft flight deck.
I'll accept that Spar, but there may be other methods available.
I was installing talking fire alarm systems over 30 years ago.
I am not an aviation guy, but from a problem solving perspective I have to wonder:
Who has the ultimate control of the aircraft? The programmer/designer or the pilot.
It feels as if the designer has decided that in the case of a disagreement between the sensors and the pilots the sensors are always right and the pilot is always wrong.
One sensor apparently failed. That should not cause a crash.
Due to the failed sensor the system put the aircraft into a dive. The pilot pulled up and turned the faulty system off. That should not have caused a crash.
A designer sitting in a safe office has decided in advance that the pilots are always wrong and has the system turn itself back on.
So from a design and implementation perspective:
A life critical system is designed with two sensors, but does not check for gross and obvious errors between the sensors.
When the pilots correctly identify a malfunction and turn the system off, the system assumes that the pilots are wrong and turns the system back on.
With such a potential life threatening change in operating parameters from previous similar craft, should there not be mandatory, specific and documented training on the changes and how to deal with malfunctions?
How were these design changes approved without iron clad assurances that the implications would be made known to the pilots?
If a pilot makes an error he has a chance to correct the error.
If the designer makes an error the pilot has much less chance to correct the error.

Back in the Reagan days and the air traffic controller's strike an air traffic controller made a public statement that was not well received by the pilots.
A friend that I had known since high school was a pilot on 737s at the time.
His comment, words to the effect that:
"Before he makes statements like that, he should strap his ass in the saddle and fly the d_mm plane!"
There may be a parallel here.

From a problem solving perspective, both the design and and the implementation of the changes were fatally flawed.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (Alistair Heaton)

Would that work with a frequency wild AC supply?
Hmm, that probably depends mostly on the device reading the resolver. Input is AC and outputs are analog AC voltage, so it would still be an AC voltage value regardless of the frequency. I'm not sure what 'frequency wild' means exactly, but I think the output voltage would not be affected a whole lot by frequency change unless it's crazy like 10-1000 hZ swings.

Brad Waybright

It's all okay as long as it's okay.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Waross, I mostly agree with you, but I'm sure you can imagine that this software/automation goes through a long and arduous design process with many people and organizations providing input and peer review. A single designer isn't just throwing something together that he thinks will work, which is what I do mostly, but the level of risk on systems I design is much lower and also, everything's on the ground so sometimes the worst thing that happens is that everything stops. But, as you say, when redundant or backup sensors are available, I always use them to error-check each other. That way an operator can at least know something is wrong with one of them and use his judgement to determine how to proceed. If this accident sequence was triggered by a single faulty sensor input when a backup is available, then I would consider that to be a design flaw.

Brad Waybright

It's all okay as long as it's okay.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

AC generators on aircraft put out a varying frequency depending on the rotation speed of the N2 shaft which connects the HP turbine to the hp compressor they are geared off. So high power it will be high frequency and low it will be low. So they call it frequency wild.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

waross you are correct, the who is in charge of the aircraft is changing with FBW and no direct linkage to the controls any more. The 737 max has direct linkage to the main flight surfaces but the trim system is now FBW. To be fair pilots have a long history of crashing serviceable aircraft for years and since the FBW has come in the accident rate has dropped.

The training about the system and the system itself I am sure will be discussed in court.


RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

"Who has the ultimate control of the aircraft?"

It's mostly the programmer, for the bulk of a typical flight, since they're often running on the auto-nav system and software. Takeoffs and landings are still in the purview of the human pilot, but even then, unless they're flying a mechanically linkaged plane, there's a truckload of firmware and hardware between the stick and actual flying surfaces.

Nevertheless, flying, in general, is safer than driving, per miles traveled. The typical numbers cited claim about 90x worse odds of dying in a car, compared to a plane. Of course, those statistics are typically cited for US carriers.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Cat IIIb is the machine doing the landing..... under supervision.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

My point to a certain extent though is that maybe it wasn't the actual sensor ( the bit of metal in the photo) that was faulty, but the analogue input card or perhaps the determination of what the analogue input was.

For control systems I use you can get say a varying voltage of 1 to 5V. That goes into the analogue input card which generates a number between say 1000 and 5000. How that number is then interpreted is down to the setting in the PLC so that in this instance 1000 means -30 degrees and 5000 means + 30 degrees. The actual input into the controller then uses these interpreted values to do the actual control.

If those setting somehow got screwed up you have your discrepancy. It's pretty clear from the trace that both AoA indicators were working as they more or less mirror each other, but were about 20 degrees apart.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

A mechanical throwing a thought out.....

Would a bad earth screw it all up?

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Since the AoA sensors were disagreeing, that should have been a failure condition for safety of flight during the design phase to determine what the system should do, and unless the system has enough smarts otherwise to get past that, it should not have been attempting to control flight with conflicting sensor data. That seems to be a serious design fault at Boeing, if that's what happened. Is there even a flight condition that can cause such readings that would be backed up by the AHRS data. Moreover, it looks like the AoA sensors were disagreeing, even before takeoff.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

to be honest if they are so mission critical on these FBW machines there should be three of them.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Resolvers are traditionally very good at coping with frequency- and voltage- wild supplies, which is one of the reasons they became so popular for safety-critical signalling (they're also less inclined to wear a hole in the track about their habitual null point before flicking their output wildly from one extreme to another than potentiometers).

The interesting thing is that the traditional way of reading a resolver signal has long since changed from being an electromechanical receiver (perhaps with its own servo loop) to being some contraption built from phase sensitive rectifiers and comparators - which may (if the designer has thought about it very much) provide adequate power supply quality and EMI resistance.

A.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (Alistair)

you can see the circuit diagram on the side of it. Its just a potentiometer.
No, not potentiometers. They look like some sort of Selsyn transmitters. (Self synchronous transmitters)
I saw tens of thousands of dollars damage done in an instant due to a reversed connection to a selsyn circuit.
The Selsyns matched and zeroed. But as soon as an error was detected the correction signal was such as to increase the error rather than to reduce the error.
I'm not saying that this was the issue here, but there are a lot of ways that a Selsyn can be improperly wired to give a faulty signal.
Some miswiring may cause a fixed offset in the indicated position.
Some errors may cause a signal reversal so that the worse the error gets, the harder it tries to make it even worse.
If the Selsyns are mounted so that they face opposite ways, eg, both facing towards the end of the wing, then either different models of Selsyn must be used on each side, or the aircraft wiring connections must be reversed on one Selsyn.
If the Selsyns are Left and Right, then installing the wrong "hand" Selsyn would most likely cause a reversed error signal.
I am assuming that the AOA sensors are plug connected. If they must be connected wire by wire then the possibility of a mistake is much multiplied.
I still can't believe that a system that is showing a 20 degree error between sensors dose not turn itself off instead of fighting the pilots into the ground.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Hello Alistair;
Thank you for your toleration of my comments.
In regards to a "Wild Frequency".
There are several ways to cope with a varying speed of an input shaft.
First, the input speed and the frequency of a synchronous generator are considered to be "locked" together.
But there are exceptions.
A generator is normally excited with DC.
If, however the generator is excited with AC then the frequency may be changed relative to the normal synchronous frequency.
Packages are available to vary the frequency of the excitation as the speed varies so as to provide a stable output frequency despite variations of the input speed.
If the frequency does change with speed changes then there are two main solutions.
1> The generator output may be rectified and then inverted back to AC at a stable frequency.
This system has been used successfully in small, permanent magnet wind generators, often with a battery bank on the DC link to provide backup.

2> All equipment may be designed to accept a varying frequency.
This is not a problem with electronics which typically rectifies the input to DC and may easily be made both voltage and frequency agile.
Large AC motors and transformers do not respond well to wide frequency variations.

You asked about a bad ground connection. That depends on the purpose of the ground connection.
In power circuits we often ground circuits to limit the voltage in the event of some other failure.
We may also ground a circuit to avoid damage due to a condition known as a "Discontinuous ground fault", a fancy name for an arcing ground fault. I doubt that this is the case in aircraft wiring but I don't know.
If a ground return is used to save a wire, then a bad ground may be the same as a bad connection in any circuit conductor. If this is common practice in aircraft then yes, but probably not for a signal circuit. A wire may be used rather than a grond return so that all circuit conductors have similar impedance.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

No problems at all sir...

Its quiet nice to be honest talking about these thigs with people that are more into the design and systems than I am, I was mostly structural when I was working as an engineer,.
If the techs want to know about a fatigue fracture I can help out but the systems stuff I am just an educated pilot.


If its saves weight then they won' use a wire. Its the same with the hydralics (which i have a bit more clue about than electrics) They will vent to a nearby low pressure line rather than run another pipe back to the reserve. The classic case which used to happen was the none retrun valve would get stuck and then the hydralic pump would explode as it was using the internal pressure behind the plate as its reference pressure. The NRV gets blocked and then the oil seapage into the pump for lubrication would gradually pressurise the internals which couldn't vent. This then meant the output was raised to 2000 psi above the internal pressure of the pump. Eventually the ouput pipe would blow off.. then they would replace the pipe... then the pump would explode.. In my experence usually over wales in in the UK.

the reason why i said a grounding fault is the fun and games i have had over the years with car electrics :D

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Still looking at those function plots from the preliminary report.
Some things to bear in mind (I didn't realized until now):
Auto Pilot was off for the entire accident flight.
In the previous flight A/P was attempted briefly then shut off for the rest.
The automatic trim is "mostly" overridden by full flaps down but not all the time (time stamp 23:23:30),
Pitch trim position varied in the top half of its range for most of the flight,
Pitch trim position became more aggressively "down" in the final 2 minutes, but crew reduced their counteracting "ups",
Airspeed was fairly constant, but seems to be slow.

I can't form a clear picture without additional information:
  • Units of scale on the trace plots
  • Position of primary flight controls (stick and rudder) for both pilot and copilot.
  • Engine power settings and RPM
In fact the ABSENCE of these plots is worrisome in itself. I am concocting in my head some crazy scenes on that flight deck.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

I'm curious about the nature of how exactly different AOA readings from each side would be accounted for under all possible real world conditions...

The airflow over any airliner's body is going to be highly variable. Apparent wind in flight can come from any vector which has a strong enough axial component to keep the airframe aloft.. surely there must be some situations where the two AOA sensors will not exactly agree because of variable airflow effects at different points on the aiframe surface.

So even with both sensors functioning, there must be some situations where perfect function provides mismatched AOA signals; that means that detecting faults is not as simple as 'AOA signals do not agree'.

Of course it's possible I've got something wrong in there but it seems logical in my mind.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

(OP)
jgKRI; I'd agree with that but there are other sensors who's inputs can corral or limit the allowed discrepancies in those areas of expected divergence. Certainly if they are disagreeing while the craft is sitting on the ground the cockpit should be alerted.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Its now being said that only one sim in the world has this MCAS system actually coded in it.

So its no wonder nobody has been able to reproduce the flight in the sim apart from boeing who has the only sim in Seattle.

It appears as such the vast majority of pilots flying the machine have had no training with the system and most have no knowedge of it or how it works never mind the failures.

Boeing is sying its covered in the QRH with excisting procedures.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (Alistair_Heaton)

Its now being said that only one sim in the world has this MCAS system actually coded in it.
So its no wonder nobody has been able to reproduce the flight in the sim apart from boeing who has the only sim in Seattle.

It appears as such the vast majority of pilots flying the machine have had no training with the system and most have no knowedge of it or how it works never mind the failures.

Wow. That just makes Boeing even more screwed on this one IMO. From what I can see a faulty sensor and run away MCAS was almost an inevitability with the design as it was. It was just a matter of when, and how it would be dealt with by the pilots.

Quote (Alistair_Heaton)

Boeing is sying its covered in the QRH with excisting procedures.
The 'existing procedures' do cover it. But the symptoms that are faced are different from most pilots would expect. Even the ones who did get it right on the previous flight still were still confused about the symptoms. They never reported run away trim.

Boeing is ass covering on this one. (Of course like most accidents there are multiple points of failure. If communication and maintenance attention on the issue had been better, there would have been a much better chance of resolving the issue and hopefully providing the feedback to prevent further incidents for all other operators.)


QF 72 had a similar incident to this. Again a imperfect design, by seemly not as bad a design as MCAS. Either way there were significant injuries and the issue was addressed by Airbus.
https://en.wikipedia.org/wiki/Qantas_Flight_72

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Despite the large number of people involved in signing off on this design I suggest that a relatively small number were actually familiar with the programing and details of the system.
I suggest that most of the people were basing their approval on descriptions supplied by the first small group.
I suspect and hope that Boeing will revise their internal procedures:
How a new design is checked:
Possible component failure.
Unintended consequences of failure.
How the above mentioned checks are verified.
How information concerning changes is supplied to pilots.
I suggest that Boeing may be in need of a lot of overall procedure changes that are not directly related to this specific failure.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

A note in AVWEB this morning says that Lion air is cancelling further orders of the 737 Max 8.
B.E.

You are judged not by what you know, but by what you can do.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

(OP)
Is Manual Stabilizer Trim completely manual? (non-electric)

What does the FEEL DIFF PRESS light indicate?

Wow, So STAB TRIM CUTOUT electrically disengages the trim?
All those poor blokes needed to do was disengage? Something seems wrong about this, surely the flight crew knew they where having a trim battle, wouldn't they head for STAB TRIM CUTOUT pretty quickly? Or do you think they didn't actually realize it was a trim issue?

Keith Cress
kcress - http://www.flaminsystems.com

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

The feel system is in there because of powered controls.


When we fly manual we fly in a trimmed condition. Which means all it needs is fingers to manipulate the controls and if you took your hand off then the plane would continue without deviation. When the aircraft is away from the trimmed position for a speed and power setting with powered controls without feel you would never know the plane was out of trim and when you released the controls the plane would then try and restore itself to the speed that it was trimmed for. So the fee system gives control force feedback which increases the further away from the trimmed position you are at.


I belive the Stabilzer trim is a metal cable to the trim tab on the elevator. On the classic you know when the aircraft is trimming because the wheel moves at high speed and is noisy and is right next to your knee. (to note I have only ever been in a 737 classic sim and on a jumpseat)

There are other things which can cause a nose down pitch one of which being an extremely forward CoG On a pax aircraft though its extremelly unusual for the CofG to change suddenly during flight. In frieghters more than a few aircraft have been lost just after departure when the load has shifted rearwards and taken the aircraft into the unstabilised area of the CoG flight envelope.

I wouldn;t say it disengages the trim more it cuts the power to it. There are situations where it jams and is in a locked position which could be due to icing on the tail plane. I have had this situation after accepting an aircraft which had be deiced with type IV fluid a couple of days earlier and they hadn;t cleaned out the trim tab joints down the back and it had turned into a gel and had frozen at altitude where the temp was -60 deg C... which is a different problem. But that also gives changing control forces as the speed changes and you alter configuration.


I don't have a clue how much trim change occurs when you go from takeoff flap to 0 flap on the 737. There will have been loads going on and alerts triggering in that cockpit. 90% of the problem is usually identifying the issue and running the correct QRH page. If you misidentify and run the wrong page it can make matters much worse. Actually i suspect if they had shut an engine down it would have likely kicked it into a none normal mode and killed this MCAS system.


RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

(OP)
Thanks for that great info Alistair!

Keith Cress
kcress - http://www.flaminsystems.com

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

https://youtu.be/A5POuch59YU

That's a 737-800 sim run for an engine fire from a couple of low hours guys I think who are doing some multi crew course It gives you an idea how the wheel moves normally.


Engine failures and fires like this example are relatively easy to sort out because the symptoms are pretty easy to solve as to the reason for the issue and the solution is obvious. ie secure the engine and fire the fire bottles

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

According to the Equipment List, the AOA sensors are identical part numbers on the left and on the right. From looking at the wiring diagrams, the Sine and Cosine output leads of the resolver in each AOA sensor are wired one direction on the #1 system into the #1 stall warning computer inputs and swapped on the #2 system into the #2 stall warning computer inputs. This is likely how the design allows one part number AOA vane to be used on either side. I do not have access to the system design to discover if the #1 and #2 AOA outputs are ever compared to each other.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

I think that question is answered in the data previously presented. The two AoA sensors disagreed while the plane was still on the ground, yet, they continued into takeoff.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Apparently it is the same part number for both sides and they can be swapped.

And also in best practise when they are swapped out a full calibration of the system should be performed which would have indicated a issue.

The parts apparently don't have an offset hole or lug to ensure correct orientation on fitting.

As usual its the full circle of screw ups which have led to the accident.

Its an option when you buy the MAX if there is AoA indications in the cockpit and if there are then you will get a comparator error if the two of them disagree. But in certain flight situations its expected that they will disagree but not constantly 20degs with wings level in the climb. In the real world a BITE check at 80 knots would have stopped this accident in its tracks with a low speed abort.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (VE1BLL)

CVR recovered.
Good. There's a running conspiracy theory about that. I'm sure those guys will decide this is not the real CVR.

Brad Waybright

It's all okay as long as it's okay.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Decent write-up at the New York Times that does a fair job of explaining how the systems work and what might have transpired:
https://nyti.ms/2UCzEom

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Another case of journalists writing an article that can impress the layperson, but just reveals their ignorance to the informed reader. They say a lot about Boeing responding to competition and pressuring the FAA, but offer no evidence to back up the claim. While I have no doubt that Boeing and the FAA interact on many levels every single day, that doesn't mean that on this particular issue anyone twisted any arms or concealed any information.

Quote:

...Boeing plans to release a software upgrade for the 737 Max, according to a person briefed on the matter...
Yay, another secret source to boost your credibility.

The write-up isn't really that bad, but has nothing new to say that hasn't already been in the NYT for the past few months. If you hadn't been following up to now, that article would be a place to start but you would need much more to get a grip on what is actually known so far. For those who have been watching this, or who know how an airplane works, it isn't even that.
The included video is next to useless. It's like nobody has any idea how an autopilot (automatic flight control system) works, so how could they possibly know what's different about the MCAS?

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

some of you might find this pilots review of the Q400 amusing.... its pretty much spot on.

https://www.reddit.com/r/flying/comments/31hgva/ho...

This iteration of the 1960/70's designs needs to stop and a full type recertification needs to occur with current standards. The crap we have to put up with in the Q400 just so that it keeps a common type rating with the rest of the DH4 types is just horrible. We could have had hot wing deicing, No condition levers just mode select buttons like the Saab 2000. But oh no crappy pneumatic boots and a cluttered cockpit made to look like a 100 but all the levers have micro switches under them instead of being connected to the system just so it a common rating for 100,200,300 and 400.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

I have to agree with Alistair Heaton that sometimes the desire to remain under an old Type Certificate can go to great "lengths". If you take a look at the two attached photos, you will see the beginning and the end of the DC-9 line. They are both under the same type certificate. The "only" differences are stretched fuselage, re-designed wings and entirely different engines. Other than that, they are identical! [That last statement was pure sarcasm - the interiors and the flight deck are entirely different as well.]

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

2
(OP)
debodine: Just use the to directly paste your pictures into a thread. Do resize them down to around 1000 pixels wide.







Keith Cress
kcress - http://www.flaminsystems.com

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

"Other than that, they are identical! "

We call that a California remodel; so long as a single wall from the original house remains, you can demo the rest of the house and quadruple its size and it's not a new build. That seems apropos, since Douglas was a California company.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

I'm not sure if this has been mentioned before, but I happened on an air crash investigations from QF72 a few weeks ago. Seemed very similar to this and resulted in modification to the programs to prevent sudden spikes from data not to cause the system to meltdown.

This (quite long) interview with the pilot concerned is enlightening as to the sheer helplessness they felt when dealing with a flight computer gone mad. https://www.smh.com.au/lifestyle/the-untold-story-...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

The flight controls in the Airbus airliners have been called "wishbones".
As in... "I wish I could go up" or "I wish I could go down" but it's up to the computer to decide if you will be allowed to do so.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

To itsmoked:

Many thanks for the instruction. I was unaware of that capability. I am very grateful for your help!

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

lion Air had another 737 go off road on the 16th of Feb 2019

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Easy fix, just control the plane like they did in the DC-3 days.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

"...a report citing data from...the cockpit voice recorder, suggests the flight crew didn't even understand what they were fighting, and may have had no idea how to override the malfunctioning system."

Doomed Lion Air flight's pilots reportedly scoured Boeing 737 Max manual as plane went down

Apparently, there was an off-duty pilot just riding along on the plane's flight the day before, who was the only one that knew what to do, but unfortunately for the poor souls on Flight 610, he wasn't there the next day.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Quote (enginesrus)

Easy fix, just control the plane like they did in the DC-3 days.

DC3: ~25,000 lb, 200 kn, piston power

737: ~190,000 lb, 450+ kn, jet power

Yeah those are aircraft that are comparable and should be compared from the standpoint of developing controls schemes.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

There isn't anything about the power or size or propulsion of a modern airplane that prevents manual flight control. The 737 elevators can be directly controlled for example. The question is whether you want to trade the family of problems associated with computer assisted flight control with the family of problems associated with full manual pilot control.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Which the answer has been overwhelmingly "no"

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

I don't know much about the flight controls, but I'd imagine manually controlling a smaller plane, such as the DC3 would not produce the same level of muscle fatigue as trying to do the same for a 737.

Anyway, there's a level of automation that has been used very successfully for decades. With properly functioning sensors, even the MCAS has apparently made flying safer, too. However, if the computer can override the controls, essentially overruling the pilots, it damn well better be getting accurate information in order to do so. There should be redundancy and cross-checks for the AoA sensors.

Personally, I think it's a bad idea to let the computer control the plane without the pilots being able to automatically override it by simply taking over the controls. They shouldn't have to try to find the right switch to turn it off so that the computer doesn't crash the plane because it's being fed faulty information.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

Did this problem start when they selected engines that were too big for the airframe?

As far as manual controls, consider the power steering in your car. Manual with power assist.
In the rare event of a failure, (usually partly the result of no attention or inspection for years and a couple of 100,000 miles) You can still wrestle the car to a safe stop.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]

This thread is terminated. Post in the continuation thread:

thread815-450258: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 2]


*************************************
Boeing 737 MAX to face first congressional hearing Link
Europe and Canada Just Signaled They Don't Trust the FAA's Investigation of the Boeing 737 MAX Link

Bill
--------------------
"Why not the best?"
Jimmy Carter

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