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>both engines would have had to fail immediately at almost exactly the same time. That's an imaginable scenario... Not only imaginable but similar has happened

by tim333 1y ago

>both engines would have had to fail immediately at almost exactly the same time. That's an imaginable scenario... Not only imaginable but similar has happened on a 787: >An ANA 787 had an unexpected dual engine shutdown after landing on January 17, 2019, activated by a system called the TCMA (Thrust Control Malfunction Accommodation), intended to shutdown runaway engines on the ground. Its logic should only activate it on the ground with weight on wheels if it senses the thrust lever is at idle but the engine is not (from https://www.reddit.com/r/aviation/comments/1ld9yb8/air_india_flight_171_crash_megathread_3/ https://www.reddit.com/r/aviation/comments/1ld9yb8/air_india...) I'm guessing something like that - a system screw up of some sort.

foldr 1y ago
That’s interesting. It’s a little unclear from the reporting whether the engines rolled back to idle (in which case electrical power would still have been available, I assume) or shut down completely. A software bug rolling both engines back to idle seems kind of conceivable. But shutting them both down completely, simultaneously, while in flight? It seems so unlikely that I’m inclined to be skeptical of the RAT claims. But obviously, no-one really knows anything at this point. Edit: I see that the WSJ now claim to have a source inside the accident investigation for deployment of the RAT: https://www.wsj.com/business/airlines/boeing-787s-emergency-power-system-likely-active-before-air-india-crash-148b7e02 https://www.wsj.com/business/airlines/boeing-787s-emergency-...
- tim333 1y ago
  There seems clear evidence the RAT was deployed from the sound on videos - you can analyse the frequencies and the like. For whatever reason in the ANA flight the engines both shut down completely https://www.aerosociety.com/news/ana-787-engine-shutdown/ https://www.aerosociety.com/news/ana-787-engine-shutdown/ not sure why you'd want to do that rather than idle them. It's reminding be a bit of the 737MAXs crashing due to a faulty sensor triggering some badly designed system. If you watch the takeoff video the plane climbs normally for about 10 seconds and then suddenly starts descending without any change of direction or rudder suggesting both engines went simultaneously which probably wouldn't be the case with fuel or birds - they found no birds when they looked. Some info on that system design https://www.pprune.org/rumours-news/617426-ana-787-engines-shutdown-during-landing.html#post10366128 https://www.pprune.org/rumours-news/617426-ana-787-engines-s... It's designed to trigger if an engine is at high thrust while the throttle is in the idle position and the plane is on the ground. Maybe there was a low probability combination of sensor failures which could explain why it only happened after much successful flying and maybe why it was when they raised the gear if that effected the on the ground sensor?

by tim333 1y ago

foldr 1y ago

That’s interesting. It’s a little unclear from the reporting whether the engines rolled back to idle (in which case electrical power would still have been available, I assume) or shut down completely. A software bug rolling both engines back to idle seems kind of conceivable. But shutting them both down completely, simultaneously, while in flight? It seems so unlikely that I’m inclined to be skeptical of the RAT claims. But obviously, no-one really knows anything at this point. Edit: I see that the WSJ now claim to have a source inside the accident investigation for deployment of the RAT: https://www.wsj.com/business/airlines/boeing-787s-emergency-power-system-likely-active-before-air-india-crash-148b7e02 https://www.wsj.com/business/airlines/boeing-787s-emergency-...

tim333 1y ago
There seems clear evidence the RAT was deployed from the sound on videos - you can analyse the frequencies and the like. For whatever reason in the ANA flight the engines both shut down completely https://www.aerosociety.com/news/ana-787-engine-shutdown/ https://www.aerosociety.com/news/ana-787-engine-shutdown/ not sure why you'd want to do that rather than idle them. It's reminding be a bit of the 737MAXs crashing due to a faulty sensor triggering some badly designed system. If you watch the takeoff video the plane climbs normally for about 10 seconds and then suddenly starts descending without any change of direction or rudder suggesting both engines went simultaneously which probably wouldn't be the case with fuel or birds - they found no birds when they looked. Some info on that system design https://www.pprune.org/rumours-news/617426-ana-787-engines-shutdown-during-landing.html#post10366128 https://www.pprune.org/rumours-news/617426-ana-787-engines-s... It's designed to trigger if an engine is at high thrust while the throttle is in the idle position and the plane is on the ground. Maybe there was a low probability combination of sensor failures which could explain why it only happened after much successful flying and maybe why it was when they raised the gear if that effected the on the ground sensor?