Posts by user "andihce" [Posts: 5 Total up-votes: 9 Pages: 1]

SLF here, retired physicist, but with much engineering (esp. systems engineering) background and considerable interest/experience in fault-finding in complex (not aircraft) systems.

I think it is helpful here to work through some possible failure scenarios in some detail. You could usefully partition these into two separate groups: “RAT was deployed” and “RAT was not deployed.” I’ll mostly follow the former here.

\xb7 By following this path, I think we can exclude incorrect flaps setting or premature flap retraction as the primary cause of the crash. It’s difficult to see how improper use of the flaps would be correlated with RAT deployment. Everything in this case points to a loss of engine thrust.

\xb7 The first question is, why did the RAT deploy? As I understand it, manual deployment by a pilot is possible, or automatic deployment caused by detection of major electrical or engine failures. I haven’t found an authoritative, detailed discussion of this, or about the time to deployment, which is relevant here as there is so little time involved.

\xb7 According to tdracer , if the primary issue was a major electrical failure, that should not have caused any engine rollback. Thus, absent pull back of the throttles (which surely would have been corrected by the pilots), there should not have been a loss of thrust.

\xb7 Thus we are left with engine rollback as the likely underlying problem. Absent other issues, a single engine rollback should not have been a major problem, so dual rollback, unlikely as it might be, seems a reasonable conclusion.

\xb7 This is consistent with the reported mayday call, although that report needs confirmation.

\xb7 It is difficult to understand a dual engine rollback. Various causes have been suggested but ruled “unlikely” here. However, it is not possible to rule out a unicorn event, like the dual engine rollback experienced by BA 38. Leaving aside the cause, it is useful to look at the consequences.

\xb7 There would have been a major loss of electrical power (apart from battery backup), assuming the APU was not running. I don’t know if is possible the APU might be used at takeoff (e,g., to unload the main engines), or if any evidence from the tail photo at the crash site provides a meaningful indication (e.g., intake door status).

\xb7 Are there other indications of loss of electrical power? The reported statements of the surviving passenger may have some relevance, but I would want to see the results of an interview by crash investigators.

\xb7 What about the loss of Flight Aware ADS-B data shortly after takeoff? There have been a few mentions of this, but not much discussion. Could this indicate loss of electrical power?



I hope this is of some use. I’m happy to defer to professionals or others here for better information/analysis.

To be clear, I am talking about the probability, given this crash has happened , that a particular item could be a cause.
The probability of something (or maybe several somethings) being a primary cause of this crash is near unity. The question, what possible causes are likely?

To take a specific item of speculation that might case dual engine rollback, fuel contamination was suggested. I don't remember all the points made in this context, but some were: no other aircraft presumably using the same fuel supply had issues; why would both engines apparently fail near simultaneously?; why would they fail just after rotation?; and so on. The consensus seemed to be, not impossible, but unlikely (presumably in the sense I just described).

Accidental (or even deliberate) fuel shutoff was also suggested. Again, the consensus seemed to be, possible, but unlikely for this type, since previous ergonomic causes of such accidental shutoff had long since been addressed.

I watched the NYT video version of the survivor interview in hospital. He is speaking in an Indian language, with a caption in English. Assuming the translation is accurate, he says he "I could feel the engine thrust increasing to go up, but it crashed with speed into the building".

​​​​​​​Note "feel", rather than "hear". Ordinarily you would first be aware of the sound of the engines spooling up, before you felt acceleration. Possibly he was subject to a somatogravic illusion as the plane accelerated downwards.

But if indeed the engines were spooling up, the question is, from what thrust level? They could have rolled back, and somehow were recovering. of their own accord or from pilot action.

All this is hanging on a pretty fine thread,

(Can't post links yet, not even permalinks, but see post #740 at present count)

I guess you have to make a post on just this one item to get it noticed!
But I agree that this piece of data deserves close attention, and is potentially confirmatory of certain scenarios which lead to electrical power loss.
I'm no expert on Flight Aware's ADS-B data, but other posts here show other flights taking off on this runway happily reporting data further down the runway and (well) after takeoff.

How else do you explain the cessation of ADS-B data from this flight from shortly after takeoff until the crash?

I think this is as interesting a line of inquiry as I've seen recently. The problem is getting the data and theory close enough to be meaningful.

For instance, what about induced drag (admittedly much complicated, I imagine, by varying ground effect) once rotation begins? A comparison with another 787-8 flight from the same runway and under similar conditions (meteorological, load, etc.) might be ideal.

Are there not tools accessible to ordinary users for making detailed such simulations, rather than a back of the envelope calculation? I daresay Boeing has made such simulations already, and have a pretty good idea of whether and when thrust loss might have occurred.