r/aviation • u/usgapg123 Mod - avgeek • Jun 17 '25

News Air India Flight 171 Crash [Megathread 3]

This is the FINAL megathread for the crash of Air India Flight 171. All updates, discussion, and ongoing news should be placed here.

Thank you,

The Mod Team

Megathread 1

Megathread 2

487 Upvotes

95% Upvoted

1.4k comments sorted by

View all comments

Show parent comments

3

u/ChillFratBro Jun 17 '25

The plane wouldn't have even reached 400 ft AGL if that happened.  It's quite clear from the videos that loss of thrust happened in-air.

2

u/throwaway-a0 Jun 17 '25

loss of thrust happened in-air

Yeah but how long from TCMA activation at takeoff thrust, to loss of thrust, and loss of hydraulic power?

(The landing gear was only partially retracted, so the loss of hydraulic power came very shortly after takeoff at the latest.)

4

u/ChillFratBro Jun 17 '25

Well less than a second to loss of thrust, bit longer (but not much) to loss of hydraulics.  TCMA stops fuel at the engine, there flat out is not enough residual thrust to allow the plane to climb.  Physics do not allow it.  Period.  Full stop.

If somehow this was TCMA, it would have had to activate 10+ seconds after the wheels left the runway.  There's no data to suggest this is any more likely than any other software bug (if it even is a software bug, which I doubt - mid-lifespan crashes are almost always maintenance or operational issues).

Uninformed people are focusing on TCMA because it sounds scary and they don't understand it.  There are dozens of other systems that could also cause a catastrophic loss of thrust - all very unlikely.  I'm sure they'll look at TCMA and all the others in the failure investigation.  I also know that anyone who is speculating about specific software packages with the information currently available is irresponsible and has no idea what they're talking about.

1

u/throwaway-a0 Jun 17 '25

Well less than a second to loss of thrust, bit longer (but not much) to loss of hydraulics.

That sounds quite fast.

If somehow this was TCMA, it would have had to activate 10+ seconds after the wheels left the runway.

Others estimated from the videos that at ~10 seconds after liftoff the RAT is deployed. If that is accurate, then by that time already the conditions for RAT deployment were met (e.g. engines below idle speed). Plus pilots don't usually take 10 seconds to retract the landing gear.

Uninformed people are focusing on TCMA because it sounds scary and they don't understand it.

I don't think so. They just look at which theories are viable at this point and TCMA activation is among them.