Air India 787 crashes on take off 7

[LittleInch]

A full 787-8 has crashed shortly after take off in ahmedabad.

Basically barely got off the ground then look like its trying to land in this video.

Air India ordered to carry out ‘additional maintenance actions’ on Boeing 787-8/9 fleet – as it happened

India’s ministry of civil aviation orders airline to carry out safety inspections on fleet with GE Aerospace GEnx engines after crash of flight 171

www.theguardian.com

Specualtion that they pulled flaps up instead of gear up and basically didn't have enough lift so it looks like a gentle stall right into a built up area.

Looks to be flaps up, slats/ nose flaps down and gear down which is very odd.

 

[Alistair_Heaton]

its the same on the A220. we have maybe twenty in the cockpit which we can touch the rest are below the floor,.

its a bit strange the ones that are in the cockpit. We have one for GPS2 but not for GPS1 which is pulled via the menu.

 

[TugboatEng]

I made the comment about generation up to 800hz and later got to thinking, the 787 has variable speed generators meaning it has inverters. Inverters don't push high fault currents so it's possible a hard fault wouldn't trip a breaker. Instead, voltage would drop to zero.

For us in maritime, our generators are required to be able to push current at 3x the nameplate rating during a transient.

 

[Alistair_Heaton]

If it's anything like ours it's mostly AC loads.

The DC is provided by TRUs.

I would think the apu starter is DC but the main engines AC.

 

[Garbage1]

My understanding is GCU takes faulty VFSG offline, prior to BPCU tieing bus with failed VFSG to another bus. The buses act independently due to variations in frequency output from each VFSG with software controlled relays.

 

[TugboatEng]

I don't think any of the VFSGs were faulty.

 

[Alistair_Heaton]

I think something commanded the emergency fuel valves to both close. And I suspect selecting the gear up was the trigger.

Quite what it triggered I really don't have a clue.

 

[Garbage1]

The potential electrical lug short in the wing spar where the generators are tied to the electrical terminal block, is where I would suspect a short or arcing condition, and not internal to VFSG. A short in that terminal block area, could trigger GCU taking generator controlling critical flight systems offline, and then a cascade of AI events.

I too believe software or electrical power loss/fault is what shuts off fuel valves at exactly the same time on both engines.

 

[TugboatEng]

I feel that the shutdown appears to have been too abrupt to have been initiated a fuel cut.

 

[Garbage1]

What is your theory? Too abrupt like water being dumped on central processing or electrical control panels, thus loss of electricity first, and fuel shutoff is just spring loaded closure? I agree fuel shutoff likely not commanded if that is what you are saying?

 

[Alistair_Heaton]

There isn't that much pipe after the fire wall max 4 meters.

It's 3/4inch pipe moving over 3000kg of fuel an hour during takeoff.

 

[Garbage1]

And even less distance from engine fuel cut off to fuel nozzles.... So commanded or un-commanded it happens very quickly

 

[Alistair_Heaton]

A normal shut down takes some time because it has compressed air blowing the fuel out the nozzles so it doesn't dry in there and gum them up.

 

[TugboatEng]

The engine takes at least a few seconds to coast down after fuel is cut, keeping pumps and generators going. The engines were operating at take-off power so the engines were near their maximum operating speed.

I don't think the crew would have initiated the retraction of the landing gear if there was an issue. That's why I believe the failure occurred completely within the one second between the wheel carriage tilting and the belly door opening.

 

[Garbage1]

Good Point. Engines spool down would not cause power generation to go from 1 to zero suddenly, unless engines came apart at same time. Thus electrical power output from common core resource area shorting is more likely, and perhaps the boom the survivor heard. What caused the boom could have been sabatoge or the water line clam shells 'rapid disassembly' as our space guys would say.

Aft galley, and bathrooms are directly above AFT EE Bay according to image below and seating plan. And there are bathrooms and galleys above forward EE and controls bay.






Below is a very good video on the B787 Electrical System , and there is a lot of good information, so I will just touch on only one key point. In addition to 4 VFSG's, there are two other independent power generation sources in the engines.

There are 3 Permanent Magnetic Generators (PMGs) providing primary power source for flight control electronics. (28 Vdc)

Then there are two Permanent Magnetic Alternators (PMAs) providing primary power for EECs, with secondary power coming from the 115VAC
bus.

Thus loss power to EEC, would mean primary power from PMAs has to be lost, and secondary power loss from 115AC bus, which would normally be supplied by VFSG's via power conversion while in flight.

Which may imply loss of common core control system had to occur, to cause loss of PMA primary power at same time as loss of secondary 115VAC power. Or loss of communications with EEC could have caused failsafe mode.






Video with lots more information:

 

[Garbage1]

The Boeing 787 Common Core System offers numerous advantages, including:

• Enhanced Integration: The CCS connects virtually all onboard systems, from flight controls to cabin management, allowing seamless communication between components. This integration reduces the complexity of wiring and the number of standalone systems, resulting in a more reliable aircraft.
• Data-Driven Maintenance: The CCS is designed to work in tandem with the Central Maintenance Computing Function (CMCF). It continuously monitors the health of the aircraft and provides real-time data to maintenance crews, helping identify and resolve issues before they become serious. This proactive maintenance approach reduces downtime and improves operational efficiency.
• Network Security: The CCS features a layered security architecture, with both the Open Data Network and Isolated Data Network designed to ensure that sensitive flight systems are isolated from less critical systems. This segmentation helps protect the aircraft from potential cybersecurity threats.

The Disadvantage is central central point failure/vulnerability.









And Dual water sources foward and above Common Core Network and Common Core Resource Cabinets.

 

[Alistair_Heaton]

I can't see how all the perm magnet sources can fail at precisely the same time.

Or the emergency fuel and hydraulic valves to shut.

The precision and lack of yaw as both engines died is actually quite hard to engineer in my opinion and experience.

 

[Garbage1]

It is looking more like a command could have been issued to roll engines back, which would have cut generating capacity for 235VAC, 115VAC, and 28VDC busses at the same time, leaving you with RAT deployment and battery backup, until APU comes on line. Engine spool down cuts primary 115VAC AC generator supporting EEC, and also cuts VFSG which is backup power supply for EEU.

 

[LittleInch]

At flight idle the engines still generate electricity - that's how it works when you're queued up waiting for take off.

There's a lot of possible reasons why they either stopped being connected to the electrical bus and responded to an incorrect signal going to idle, but we're talking major melt down of one or more components. All the more surprising that nothing seems to be leaking or being state with certainty. initial report due out this Fri, but I'm not expecting much in the way of useful detail myself.

 

[Garbage1]

Generators/Alternator output would be reduced at idle vs full throttle takeoff, which could have triggered another set of automatic reactions, since AI in control.

Engines rolled back to idle, may not be generating enough electricity to raise the landing gears for example?

 

[Alistair_Heaton]

had a technician rated on the jumpseat yesturday.

He suggested it could have been the weight on wheel logic that triggered the start of the events.

There is no output decrease from the generators dependant on power setting that i can see. I suspect its a fadec function to increase fuel flow to cover any drop to maintain idle turbine speed.