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.

 

[Garbage1]

All power comes from 4 235vac generators. There are no separate 28vdc generators.

Ok AliStair that makes sense. Yes external 115V power when starting, and no engine driven VFSG electrical output. Around N1 or so transition to PMA's and PMG's. PMA's and PMGs are primary, with VFSG's being secondary for EEC, after engine is running.

So Tug's statement about no 28Vdc Gernerators is Not why he won this week's Congratulations for helpful posts?

 

[Alistair_Heaton]

I don't think it needs to be live until things are ready for the fuel to get turned on which is around 20%. You only need the air starter valve to get HP air to get things turning or AC power on the 787 which can be controlled externally.

To be honest these engines require very little input from a human compared to old ones which needed a knack and timing quite often to get them going without over temping or burning the ignitors.

There are lots of these systems and redundancy methods on FBW aircraft which sometimes the technicians don't even know about never mind the stick monkeys.

 

[TugboatEng]

Remember VSFG is a starter generator. The VSFG's are not providing power during the start phase, they are a load. The battery starts the APU and the APU provides the power to start the engines and operate FADEC until the start is complete.

 

[Garbage1]

Yes engine VFSG's are loads during starting.

Based on multiple sources, primary power for flight controls are from independent 28Vdc PMGs located on the engines. 28Vdc buss power supplied by VFSG's is only secondary power source for flight controls.

Primary Power for EEC's is provided by independent 115VAC PMA's located on engines.

Starting RPM should be sufficient for EEC's to control fuel flow at appropriate time

We differ in opinion on primary power sources for flight controls and EECs.

What we have in common is we both used the same questionable internet sources for our opinions.

I have not seen anything posted that conclusive proves which of our opinions could be correct?

 

[TugboatEng]

Multiple sources is not an indication of quality. Articles use a lot of circular referencing nowadays.

Maybe it was missed but this website has the most complete description of the electrical systems on the 787. There are no PMA or PMGs.

How to master B787 Electrical System - SkyhighTEX - Knowledge Base

It is a highly refined and automated aircraft, with automatic system configuration and load balancing. All systems of the aircraft are electrically powered;

kb.skyhightex.com

You can check the minimum equipment list shared by Alistair. There are only VFSG's on the list.

 

[Garbage1]

Here is screen shot from your linked site talking about 28 Vac PMG's and 3 of them and they are the primary source of independent power to the flight controls.

Your link also talks about there being three 28VAC PMGs. My link says three 28VDC PMGs also.

So one of the sites is wrong on DC vs AC it appears.

Bottom line is both your source and my source state there are 28V Independent generators feeding primary power to flight controls, which conflicts with your statement that all power comes from 4 235VAC generators?

 

[TugboatEng]

It's weird but that doesn't say that the airplane has PMGs. It's explaining that the independence of the VFSGs eliminates the need for 28v PMGs.

 

[Garbage1]

Boy it is getting deep here.

 

[TugboatEng]

People are still speculating about mast bumping on the Hudson river helicopter despite us having images of the top deck of the helicopter separating from the airframe...

 

[Garbage1]

There does seem to be an abundance of 'useful idiots' for hire, whenever protest and riots are desired by ...........

 

[Alistair_Heaton]

If something isn't mentioned in minimum equipment list it means if it's broken you can't dispatch.

That doesn't mean it's not there.

 

[TugboatEng]

I get that but don't you think generators that operate the FADEC would have some mention in the MEL?

With that said I am looking for mention of the 235v to 28v transformers in the MEL and haven't found them yet.

BUT! I don't think that's relevant because it seems the RAT deploys in failure of the 4 VFSGs and we do know the RAT was deployed so we do know 4 VFSGs went offline.


Maybe an automation fault tripped them but they also have some type of mechanical disconnect device as I learned from the MEL. I wonder how that is operated. Is it a magnetic clutch? Does a mechanic have to open the cowling and remove a coupling? Could an interruption of power cause a VFSG to disconnect from its transmission?

The startup time for the APU is 90 seconds. It seems like the aircraft got itself into a situation where it needed an APU but due to the stage of flight it had less than 40 seconds to wait.

 

[Garbage1]

Ok, lets look at this from a different angle. We have been saying all along that the 1 second loss of electricity to EEC caused the spring loaded fuel valve to close. Further we have been saying any interruption of electricity during power transfer, would cause spring loaded fuel valve to close. Thus it would follow that a transfer of electricity from APUs to engine VFSGs would cause fuel valve to close momentarily and result in loss of engine fuel. Thus the need for PMAs and PMGs.

This suggests that engines need to be started on primary power for EEC to sustain engines after start. This transfer of electricity at 40,000 ft would provide time to restart the engines during transfer to backup electricity.

Transfer of power would result in rebooting of EEC it would seem, causing further delay.

We just don't have adequate quality of sufficient accurate and complete information to know, which is exactly where manufactures and governments want us to be.

 

[LionelHutz]

You've been saying that. I don't believe they would use spring loaded fuel valves because that'd be really dumb to have on a plane where you want the engines to keep running.

 

[Garbage1]

Is the airframe or engine more important when there is an engine fire?

With loss of electrical power to EEC during an engine fire, do you want to keep dumping fuel on engine fire, or would you prefer to automatically stop fueling the fire to protect airframe for use with other engine or glider mode?

Here is FAA airworthiness directive requiring redeigned/different part replacement of fuel valves on B787. This was required to prevent fuel valve from failing in open position, thus feeding a fire.

Federal Register :: Request Access

www.federalregister.gov

 

[TugboatEng]

The engines use FADEC. It is most likely PWM to the nozzles that determines the amount of fuel the engines receive. No power means no pulse which means no fuel. That is it. No springs or fuel cut valves required. We know there was no power because the RAT deployed.

We're fighting this problem in the tugboat industry. A millisecond lapse in power or even a run signal on an electronically controlled engine means the engine shuts down instantaneously. This is very dangerous due to our asymmetric thrust capabilities and our close proximity to fast moving ships.

 

[Alistair_Heaton]

"I get that but don't you think generators that operate the FADEC would have some mention in the MEL?"

No because you ain't going flying with it broken.

Mel only has things that can be broken and you can still go.

You can get redundancy loss items which may indicate something is broken which downgrades and requires you to operate in a particular manner. Eg there may be a channel in the fadec not working on one engine which will result in a redundancy loss info and in the mel. If two are gone it will turn into a red master warning engine fault on the ground. Which isnt mentioned in the mel.

 

[Garbage1]

The engines use FADEC. It is most likely PWM to the nozzles that determines the amount of fuel the engines receive. No power means no pulse which means no fuel. That is it. No springs or fuel cut valves required. We know there was no power because the RAT deployed.

We're fighting this problem in the tugboat industry. A millisecond lapse in power or even a run signal on an electronically controlled engine means the engine shuts down instantaneously. This is very dangerous due to our asymmetric thrust capabilities and our close proximity to fast moving ships.

So that begs the question of how does B787B use APU's to power EEC during startup, and then transition to engine VFSG's to power EEC without a millisecond of lapse occurring during electrical power transition?

 

[Alistair_Heaton]

It doesn't.

The eec comes online at 8% n1 during start. It doesn't actually do anything until 20% when the fuel metering valve opens and the ignitors light up.

 

[TugboatEng]

My understanding is that the APU powers the EEC until the engine is running. Once running, the VFSGs go on to the bus in parallel with the APU. If all 4 VFSGs are operational the APU is shutdown. If one VFSG is non-op the APU stays running for the duration of the flight. There is no interruption of power.