Air India Crash

[esmozz]

I've been pondering the vapour lock theory and whilst initially unconvinced now I'm not so sure.

I've operated the B737 at temperatures up to 45C and airfield elevations of up to 6000 feet. (both at the same time, actually). I've only been vaguely aware of vapour lock because I've never really considered it an issue. Certainly the 737 can do it without any problems from my experience.

Fuel has a minimum and maximum temperature (in the video its stated at +49C). I've never seen fuel temperature even get near that. From my experience it's the fuel minimum temp that can be an issue (but even then, very rarely).

But the maximum temp of +49C refers to the Jet-A1 specification which is by far and away the most common fuel used in commercial aviation. There are many other types (Jet B, JP5, JP8, RT or TS-1 for example). RT and TS-1 are Russian specifications. I know these fuels have different minimum temps and I suspect different max. temps as well. They will all behave slightly differently as well.

I would guess that the 787 in the accident was refuelled with Jet A1 but really have no idea if that's true.

Although I'm struggling with the idea of both engines failing at the same time, I can sort of see it with the vapour lock idea. At least, with the idea of them failing in close proximity. Particularly if using a fuel that's not as robust as Jet-A1. Not being an expert in aircraft fuel types, I'm assuming Jet-A1 is the most common fuel simply because it's the safest specification.

So I really don't know now.

 

[200sols]

Although I'm struggling with the idea of both engines failing at the same time, I can sort of see it with the vapour lock idea. At least, with the idea of them failing in close proximity. Particularly if using a fuel that's not as robust as Jet-A1. Not being an expert in aircraft fuel types, I'm assuming Jet-A1 is the most common fuel simply because it's the safest specification.

Them both failing at exactly the same moment is the flaw in most theories right now.

 

[BUDFORCE]

The longer it takes to release the first information the more I suspect there is some design fault/software fault.

If it were foul play or pilot fault they will get it out there as quickly as possible to exonerate themselves.

 

[Penfold101]

Them both failing at exactly the same moment is the flaw in most theories right now.

Which points to a flaw in the aircraft side sending the command to shutdown to both engines, or operating the T-handle to shut off fuel, electrics and hydraulics.

 

[esmozz]

Them both failing at exactly the same moment is the flaw in most theories right now.

That's the part that get's me as well. I just don't know.

An engine failure on any large commercial type of aircraft with engines significantly offset from the longitudinal axis of the aeroplane is marked by a rapid onset of yaw towards the failed engine, followed by roll in the same direction, particularly on swept wing aircraft (As the aircraft yaws the wing on the working engine side moves forward into the airflow, effectively reducing its sweep and increasing its lift, the opposite happens on the failed side).

The FBW system on the 787 has a function which will correct for this if it detects an engine failure, in order to significantly reduce pilot workload.

My point being, unless the engines failed at exactly the same time you should see the aircraft shimmy or wobble as the engines fail (one, then the other). Neither the automatic system or pilots would be able to correct for any asymmetric thrust perfectly. As well as seeing significant deflection of the rudder to counter the yaw.

As I linked to earlier the thread, this system has been linked to engine rollbacks an a different aircraft type. Albeit in conjunction to the air/ground logic switching into ground mode after landing, so no major repercussions.

So I really don't know - this is all speculation.

 

[esmozz]

Which points to a flaw in the aircraft side sending the command to shutdown to both engines, or operating the T-handle to shut off fuel, electrics and hydraulics.

Right now, with the very limited info available, I'd say yes. And I'd discount the latter due the the pilots MAYDAY call. I think he would have said something different had that been the case.

 

[200sols]

The longer it takes to release the first information the more I suspect there is some design fault/software fault.

If it were foul play or pilot fault they will get it out there as quickly as possible to exonerate themselves.

Conversely if it is a design/software fault Air India want it out as quickly as possible to exonerate themselves.

 

[Penfold101]

Right now, with the very limited info available, I'd say yes. And I'd discount the latter due the the pilots MAYDAY call. I think he would have said something different had that been the case.

Yes, as in uncommanded operation, if there’s even a box which has the ability to do that.

Commanded operation is not something I’m even going to consider for many reasons.

 

[esmozz]

The longer it takes to release the first information the more I suspect there is some design fault/software fault.

If it were foul play or pilot fault they will get it out there as quickly as possible to exonerate themselves.

Boeing will want that. Air India and the Indian government will want the exact opposite.

Right now, teams of very very expensive lawyers are burning the midnight oil (at 1000's of dollars per hour, I imagine) prepping for the ensuing legal battle.

The amount of money involved in these sorts of things is eye watering (I would guess in excess of a billion $)

 

[Penfold101]

Conversely if it is a design/software fault Air India want it out as quickly as possible to exonerate themselves.

The difficulty may come, if it IS uncommanded shutdown by a black box, it’s whether the recorder has enough information to extrapolate why it happened. Some stray line of code buried deep Will be ridiculously difficult to track down and replicate.

 

[NickK]

I suspect not as well. However, Boeing is so integral to the US military industrial complex that it's arguably to big to fail. My guess would be it would be broken up.

I should point out that this is all entirely speculation on my part.

Trump will buy them -- otherwise who would service his Qatar **** palace? He's not going to get a Air Force One Airbus.

 

[NickK]

I've been pondering the vapour lock theory and whilst initially unconvinced now I'm not so sure.

I've operated the B737 at temperatures up to 45C and airfield elevations of up to 6000 feet. (both at the same time, actually). I've only been vaguely aware of vapour lock because I've never really considered it an issue. Certainly the 737 can do it without any problems from my experience.

Fuel has a minimum and maximum temperature (in the video its stated at +49C). I've never seen fuel temperature even get near that. From my experience it's the fuel minimum temp that can be an issue (but even then, very rarely).

But the maximum temp of +49C refers to the Jet-A1 specification which is by far and away the most common fuel used in commercial aviation. There are many other types (Jet B, JP5, JP8, RT or TS-1 for example). RT and TS-1 are Russian specifications. I know these fuels have different minimum temps and I suspect different max. temps as well. They will all behave slightly differently as well.

I would guess that the 787 in the accident was refuelled with Jet A1 but really have no idea if that's true.

Although I'm struggling with the idea of both engines failing at the same time, I can sort of see it with the vapour lock idea. At least, with the idea of them failing in close proximity. Particularly if using a fuel that's not as robust as Jet-A1. Not being an expert in aircraft fuel types, I'm assuming Jet-A1 is the most common fuel simply because it's the safest specification.

So I really don't know now.

An alternative is that the tanks had condensation inside, causing either corrosion or icing but this was on the ground.

 

[Kenai]

The longer it takes to release the first information the more I suspect there is some design fault/software fault.

If it were foul play or pilot fault they will get it out there as quickly as possible to exonerate themselves.

It'll be the AAIB that will be choosing what or when to release updates now, not Boeing or Air India, so I wouldn't read all that much into how long it's taking them to get anything out, the investigation bureau won't have any particular vested interest in exonerating (or not) anyone involved.

 

[NickK]

The difficulty may come, if it IS uncommanded shutdown by a black box, it’s whether the recorder has enough information to extrapolate why it happened. Some stray line of code buried deep Will be ridiculously difficult to track down and replicate.

You'd have thought that the system sends hashed checksums as part of the diagnostics on the blackbox.

 

[Penfold101]

You'd have thought that the system sends hashed checksums as part of the diagnostics on the blackbox.

I’m not questioning the veracity of the data, it’s whether it’s recording the right parameters from the myriad of black boxes to figure out what caused the engines to shut down. A signal maybe been sent, but figuring out WHY that signal was sent is another matter. You’d also need to know the exact software build of that particular box, what updates it may have had etc.

 

[Werewolf]

I've been pondering the vapour lock theory and whilst initially unconvinced now I'm not so sure.

I've operated the B737 at temperatures up to 45C and airfield elevations of up to 6000 feet. (both at the same time, actually). I've only been vaguely aware of vapour lock because I've never really considered it an issue. Certainly the 737 can do it without any problems from my experience.

Fuel has a minimum and maximum temperature (in the video its stated at +49C). I've never seen fuel temperature even get near that. From my experience it's the fuel minimum temp that can be an issue (but even then, very rarely).

But the maximum temp of +49C refers to the Jet-A1 specification which is by far and away the most common fuel used in commercial aviation. There are many other types (Jet B, JP5, JP8, RT or TS-1 for example). RT and TS-1 are Russian specifications. I know these fuels have different minimum temps and I suspect different max. temps as well. They will all behave slightly differently as well.

I would guess that the 787 in the accident was refuelled with Jet A1 but really have no idea if that's true.

Although I'm struggling with the idea of both engines failing at the same time, I can sort of see it with the vapour lock idea. At least, with the idea of them failing in close proximity. Particularly if using a fuel that's not as robust as Jet-A1. Not being an expert in aircraft fuel types, I'm assuming Jet-A1 is the most common fuel simply because it's the safest specification.

So I really don't know now.

IIRC most "temperature" ranges for things like fuel are based on the fuel temp, and if as was reported it was what 40c(?) outside* at the time of the accident, the temperature of the fuel in the tanks and wings could have been much higher as surface temperature (and thus temperature behind that surface) can be significantly higher than the measured air temperature (think of how road/pavement surfaces can be hot enough to cause burns in bright sunlight even if the measured temperature is only 30c).
From memory there are rules about things like running the cabin air-conditioning under even normal circumstances because the air-conditioning units can raise the temperature of the fuel in the tanks on some aircraft (IIRC a lot of models have them fairly close to each other as in flight at altitude that heat helps the fuel or something). I think there was a major accident a while back that was caused by the combination of the fuel being too warm in an improperly vented tank (causing it to evaporate and mix with the air reaching the critical ratio) and a spark from a faulty wire despite in theory the weather not being warm enough to cause the critical amount of evaporation.

It wouldn't be the first time that an accident involving fuel or engines has been caused by temperatures despite the fact that the outside temp was withing the range allowed for.


*I think I saw it was nearly 40c in the shade, which means surfaces in direct sunlight were possibly hot enough to cause burns/be painfully hot (like touching the top of your car or getting inside in when it's been in the sun even at just 20-25c you notice a significant difference between air temp and surface/internal temps).

 

[esmozz]

It'll be the AAIB that will be choosing what or when to release updates now, not Boeing or Air India, so I wouldn't read all that much into how long it's taking them to get anything out, the investigation bureau won't have any particular vested interest in exonerating (or not) anyone involved.

The investigation will be led by the Indian equivalent of the AAIB, with experts from other countries similar organisations (In this case the UK AAIB, due to the number of UK citizens and the NTSB, due to the aircraft being manufactured in the US). There may be others involved as well.

But in an accident of this magnitude there is always a political angle, in this case the Indian government having a stake in the outcome. In previous accidents there has been significant pressure to find the 'right' answer. I'm not saying that will happen here but it has happened in the past.

The example I'm thinking of is the 737 crash at Schiphol airport, where a faulty rad alt, led to an unnoticed reduction in thrust to idle and subsequent stall. It was widely considered that the pilots were to some degree negligent but that was rejected by the Turkish led board of inquiry.

I'm not casting dispersions on the Indian governments ability to lead an impartial investigation because I simply don't know enough about it, but will just say it could be a factor to consider.

 

[esmozz]

IIRC most "temperature" ranges for things like fuel are based on the fuel temp, and if as was reported it was what 40c(?) outside* at the time of the accident, the temperature of the fuel in the tanks and wings could have been much higher as surface temperature (and thus temperature behind that surface) can be significantly higher than the measured air temperature (think of how road/pavement surfaces can be hot enough to cause burns in bright sunlight even if the measured temperature is only 30c).
From memory there are rules about things like running the cabin air-conditioning under even normal circumstances because the air-conditioning units can raise the temperature of the fuel in the tanks on some aircraft (IIRC a lot of models have them fairly close to each other as in flight at altitude that heat helps the fuel or something). I think there was a major accident a while back that was caused by the combination of the fuel being too warm in an improperly vented tank (causing it to evaporate and mix with the air reaching the critical ratio) and a spark from a faulty wire despite in theory the weather not being warm enough to cause the critical amount of evaporation.

It wouldn't be the first time that an accident involving fuel or engines has been caused by temperatures despite the fact that the outside temp was withing the range allowed for.


*I think I saw it was nearly 40c in the shade, which means surfaces in direct sunlight were possibly hot enough to cause burns/be painfully hot (like touching the top of your car or getting inside in when it's been in the sun even at just 20-25c you notice a significant difference between air temp and surface/internal temps).

I think the fuel is cooled by either in the storage tanks or as it's pumped in to aircraft fuel tanks, I'm not really sure. All I can say is, I've seen temperatures of 45C outside and the fuel temp (there's a temperature gauge in the flight deck) has never even been close to the outside air temperature.

The aircraft had about 50T of fuel onboard and that's going to take a long time to heat up (I'm sure somebody smarter than me could do the math)

I'm not aware of any limitations regarding air conditioning pack (either by APU or engines) use with regard to fuel temperature but I don't know a great deal about the finer details of other aircraft types other than the one's I've been rated on, so it could be. However fuel is often used to cool the engine oil in flight, so you may be thinking of this.

Fuel vapour in the tanks has caused accidents in the past, the particular example I'm thinking of is TWA800, a 747 operating from New York (I think). A spark from a faulty fuel pump caused an ignition of fuel vapor in the centre tank with the total loss of the aircraft. This led to the introduction of nitrogen generators to fill the empty volume in the tanks with inert gas to prevent it happened again. (And also a change to the operating procedures regarding how centre tank fuel pumps are handled)

I'm sure the 787 has such a system. Interestingly however, it is a MEL item (at least on the 737) and the aircraft can operate with it being unserviceable for a period time.

Either way, one thing I am sure of is the the fuel tank didn't explode in this case.

 

[Penfold101]

It’s worth mentioning that the aircraft flew in from Delhi that morning, and whilst only a short flight (1:10) it would have chilled what fuel was in the tanks before the uplift to 50t to fly to London.

 

[Sinbad2000]

It’s worth mentioning that the aircraft flew in from Delhi that morning, and whilst only a short flight (1:10) it would have chilled what fuel was in the tanks before the uplift to 50t to fly to London.

One of the risks mentioned in the vapour lock papers/videos is short turnarounds...?