[News] Air India flight AI171 Ahmedabad -> London Gatwick crashed

[Triggaaar]

I've seen suggestion the RAT was out? Which would indicate electrical failure, but not alleged thrust loss

Does double engine failure not also result in RAT deployment?

 

[PILTDOWN MAN]

I've seen suggestion the RAT was out? Which would indicate electrical failure, but not alleged thrust loss imho though that's also very grainy footage and certainly not yet conclusive. Gear not being up is still the elephant in the room, as any normal take off or loss of thrust and gear up (to reduce drag) is first action on being airborne (unless it wouldn't go up?)

It's also not to long after being airborne it starts to sink, so if engines were working and producing thrust on runway, for them both to fail within seconds of being airborne, whilst not impossible, would be so extremely rare. If anything happened before V1 or thurst loss prior, they'd reject take off.

Sorry to others in getting technical with @PILTDOWN MAN !

I don't know the 787 intimately, I do know it's fly by wire, so you haven't got manual reversion hydraulic overide of controls without electrics working.
A double mechanical engine failure (birds) is super rare. Fuel contamination less so, but that should be checked on ground and it didnt seemingly flame out engines before getting airborne.

The "total electrical failure" theory, i struggle to believe could be a cause of total thrust loss even if RAT is out (which would indicate electrical power failure) as i can't imagine the 787, like other aircraft, wouldn't have sufficient critical systems redundancy for loss of engine driven AC electrical generators....

Electrical failure would make your day hard for sure, but it wouldn't normally stop the engines.
The engine fuel metering and FADEC are always normally connected to the hot battery bus on Boeing ot Airbus, the absolute essential systems which you can't switch off and which will give you at least 60 mins on battery power (DC-AC via invertor) with total AC generator power loss.

Still more questions than answers at this stage. Nothing yet seems overly clear or adds up.

https://www.pprune.org/engineers-technicians/602364-787-fuel-system-question.html

Appears that both engines would have fuel from the centre tank as it has a higher pressure output, I find that surprising but this pilot does raise it.

 

[Guinness Boy]

If it was double engine failure, I'd hope they'd ground all of the same aircrafts, unless they were absolutely sure it couldn't happen to another plane.

There are two different 787 engine suppliers, GE and Rolls Royce. You’d have to know which this plane used, which I expect they do.

One reason you couldn't hear the engines, is because the recording was someone filming another recording, so the audio was terrible.

If you look at the video @Chicken Run posted that shows the “pure” video with the RAT deployed.

 

[Triggaaar]

There are two different 787 engine suppliers, GE and Rolls Royce. You’d have to know which this plane used, which I expect they do.

Well yeah, you'd hope they know

If you look at the video @Chicken Run posted that shows the “pure” video with the RAT deployed.

Yes I've seen it. Can you not hear the engines in that?

 

[peterward]

https://www.pprune.org/engineers-technicians/602364-787-fuel-system-question.html

Appears that both engines would have fuel from the centre tank as it has a higher pressure output, I find that surprising but this pilot does raise it.

That is correct. Centre is higher pressure so centre tank is always first to drain when all pumps on to keep stability in wings (whose fuel burns last)

 

[Guinness Boy]

Well yeah, you'd hope they know




Yes I've seen it. Can you not hear the engines in that?

I’m not an expert but I hear a propeller noise, not two jet engines.

 

[Triggaaar]

I’m not an expert but I hear a propeller noise, not two jet engines.

I don't know any better, but when the captain giving that video gives reasons why he thinks it was engine failure (he can see the RAT, he can hear the RAT, the pilot said he lost thrust, the witness said there was a bang and light flicker), he didn't say 'I couldn't hear the engines'.

 

[peterward]

Does double engine failure not also result in RAT deployment?

While no expert in 787, yes it could (if RAT was out?) It would be so as loss of AC power (that comes from AC generators on both engines.

My point was more that some people were suggesting the total loss of electrical power could be the cause of a double engine failure, it shouldn't be. That's putting cart before the horse.

Double engine failure will secondary cause electrical failure, as both engine AC generators will stop working, not the other way around in my experience.

If both engines AC generators failed, electrical power fails, but engines should still run and still produce thrust.

If engines fails first both engine and electrics fail.

Standby battery power is then automatic.

 

[Chicken Run]

Well yeah, you'd hope they know




Yes I've seen it. Can you not hear the engines in that?

No u can hear the RAT engine which sounds like a single prop

 

[Triggaaar]

No u can hear the RAT engine which sounds like a single prop

I think I can hear both

 

[PILTDOWN MAN]

I think I can hear both

Two jet engines at takeoff thrust would be heard over a small prop.

 

[Triggaaar]

Two jet engines at takeoff thrust would be heard over a small prop.

So why didn't the Captain bother to mention it?

 

[PILTDOWN MAN]

So why didn't the Captain bother to mention it?

The captain of the plane or the one in the video?

 

[Triggaaar]

The captain of the plane or the one in the video?

The one analysing the video in the video

 

[Chicken Run]

The one analysing the video in the video

He did He even showed test videos of low flying jets with the RAT deployed

 

[PILTDOWN MAN]

The one analysing the video in the video

He did. He said the sound was the prop not engine sounds. He put it at the top of his theory, double engine failure. Even mentioned fuel contamination which I have alluded to.

Years ago the procedure was that each engine was fed from separate fuel tanks on takeoff. This was so they remained independent. When Extended Range Twin Engine Aircraft (ETOPS then changed to EROPS) each aircraft type and airlines had to prove their reliability. This extended to procedural things such as I've mentioned above. As long range twin engine aircraft are now the norm this will be down to the amount of data proving their safety. Any aircraft should be able to takeoff at max weight on 50% of available power B787 one engine, A380 on 2.

At the beginning of licensing twin engine aircraft they had to prove their safety of flying on one engine over a period of distance i.e. from the middle of the Atlantic to an airport. There used to be an area in the middle that was somewhat dodgy many felt. Thankfully things have improved.

The old B747 especially powered by the Pratt and Whitney engine were considered under powered and I happen to have witnessed this incident as I was outside Hangar 6 at the time. The no. 4 engine surged causing a fire and the exhaust cone dumped on the runway. It nearly crashed at Russ Hill narrowly missing a house. The tower thought it had crashed. It didn't and somehow managed an emergency landing.

https://assets.publishing.service.gov.uk/media/5422f68ae5274a1317000623/4-1989_N605PE.pdf

 

[Triggaaar]

He did He even showed test videos of low flying jets with the RAT deployed

I think you've misread what I posted. I know he posted videos of jets with RATs, and said that he thought that was deployed on the Air India flight. He says he thinks it's double engine failure. But presumably the engines losing power would mean engine failure even if they're still running to some extent?

He did. He said the sound was the prop not engine sounds. He put it at the top of his theory, double engine failure. Even mentioned fuel contamination which I have alluded to.

I don't think he says that the engines can't be heard. He said that you can hear (and see) the prop (and that top of his theory) but I don't think he said there's no sound of the jets. Maybe there is no sound of the jets at all, or maybe they're quieter than they should be. I just don't think he said.

 

[PILTDOWN MAN]

I think you've misread what I posted. I know he posted videos of jets with RATs, and said that he thought that was deployed on the Air India flight. He says he thinks it's double engine failure. But presumably the engines losing power would mean engine failure even if they're still running to some extent?



I don't think he says that the engines can't be heard. He said that you can hear (and see) the prop (and that top of his theory) but I don't think he said there's no sound of the jets. Maybe there is no sound of the jets at all, or maybe they're quieter than they should be. I just don't think he said.

But he said repeatably twin engine failure. If both engines had failed they would still be turning unless seized and give off a whistling sound not a thrust one. In that video if the sound is right as he indicates those engines are not creating any thrust.

 

[Triggaaar]

But he said repeatably twin engine failure.

I know!

If both engines had failed they would still be turning unless seized and give off a whistling sound not a thrust one.

Ok, I have no idea what sound they'd make.

In that video if the sound is right as he indicates those engines are not creating any thrust.

He says he thinks it's engine failure, and gives some reasons. One of the reasons is that the RAT deploys. But he also says there are other things that could cause RAT deployment, so he needed more reasons as evidence that it was engine failure, not something else. If he noticed that the audio from the jet engines was far lower than it should have been, I'm surprised he didn't say so, that's all.

 

[SkirlieWirlie]

The facts to date are that the plane crashed on take off, the video evidence, which is all the general public have to go on, strongly suggests that the RAT deployed, which suggests some sort of significant mechanical/electrical failure.

Until the official report is published, not sure what anyone else wants, or needs, at this stage.