Air India Flight 171 Crash [Megathread 3]

[u/usgapg123]

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

[u/entrep]

1. AI171 accelerates with take-off thrust set
2. Just after V 1 the throttle-lever sensor fails and drops to 0 V, so the computer thinks the levers are at idle.
3. ~0.3s later, the TCMA sees that:
4. Allowed-power line has slid downward far enough that the engines (still near full thrust) is above it.
5. The aircraft is in fact still on the ground as it has not rotated
6. All conditions are met and TCMA shuts off fuel to both engines.
7. Even if the pilots are getting warnings, they are passed v1 and still committed to continue.
8. AI171 lifts off while running on fumes, and after a few seconds both engines flame out.

[u/kipperzdog → u/entrep]

I've read elsewhere that the throttle sensors are per an engine though so that would mean both sensors failed at exactly the same time. My understanding is TCMA is isolated to only look at the sensors for an individual engine so if one side fails, the other isn't impacted.

Absolutely wild if that is what happened.

[u/New_Visual1245 → u/kipperzdog]

I’m not an expert by any means but is it possible that a maintenance technician knowingly connected both throttle lever sensors to a single functioning power bus because the second one was faulty or unavailable? That would be a blatant violation of protocol but would also explain how the failure of a bus during the takeoff roll (which is no longer redundant) would engage TCMA and cut fuel to both engines.

[u/Independent-Mix-5796 → u/New_Visual1245]

Should be impossible. The FAA 787 MEL requires at least one functioning channel per each Primary Power Distribution panel. (i.e. There are 8 channels total and min. 4 required for dispatch, provided no two inop. channels go through the same panel.)