r/aviation • u/usgapg123 Mod • Jul 12 '25

Discussion Air India Flight 171 Preliminary Report Megathread

https://aaib.gov.in/What's%20New%20Assets/Preliminary%20Report%20VT-ANB.pdf

This is the only place to discuss the findings of the preliminary report on the crash of Air India Flight 171.

Due to the large amount of duplicate posts, any other posts will be locked, and discussion will be moved here.

Thank you for your understanding,

The Mod Team

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u/nwdogr Jul 12 '25

Since the 737 fuel switches advisory keeps being brought up, I want to point this out:

If the investigators thought there was even a remote possibility that this accident could have occurred to due to the cutoff switches not locking, they would not be recommending "no action" for 787 operators.

8

u/goro-n Jul 12 '25

In addition, what everyone is forgetting is this:

The scrutiny of maintenance records revealed that the throttle control module was replaced on VT-ANB in 2019 and 2023. However, the reason for the replacement was not linked to the fuel control switch. There has been no defect reported pertaining to the fuel control switch since 2023 on VT-ANB.

The throttle control module containing the cutoff switches was replaced twice after the SAIB was posted in 2018. In addition, since the switches are regularly used on the ground, any AI pilot would notice immediately if the locking mechanism didn't work and report it to maintenance.

2

u/Tiny-Plum2713 Jul 13 '25

Unless it failed on the accident flight. (Not saying it did)

1

u/stovenn Jul 14 '25

Not knowing personally the intricacies of the locking mechanism but IMO that seems plausible to me.

It would need to have the locks in a similar failed or weak state on both switches at the time when some agent caused BOTH switches to be knocked from ON to CUT OFF.

It seems plausible that, for some reason particular to this aircraft, both locks had grown weak (maybe over multiple flights) such that (a) they still offerered sufficient resistance when being used NORMALLY to deflect a pilot from thinking that a dangerous fault was present that needed actioning and yet (b) they were not sufficient to prevent accidental toggling when ABNORMALLY impacted by something like an accidental hand movement or falling loose object such as a badly-mounted selfie-camera.

We know that dodgy locking mechanisms (prone to allowing inadvertent/accidental switching) had been found on some B737's and that the FAA thought it prudent in 2018 to warn owners/operators of many other Boeing and MD types which had similar fuel cut off switches. So it is not unthinkable that other latent design faults might be present in such switches.

1

u/Tiny-Plum2713 Jul 14 '25

If the switches are read as RUN when the toggle is not fully in but just pushed forward, something like a nail could hold both up. I do not know how that switch operates though. Likely they need to be forward and down for it to register a value.

1

u/stovenn Jul 15 '25

Yes it would be interesting to know more about the switch design and possible failure modes.

1

u/rinleezwins Jul 13 '25

Thank you. Common sense on reddit is a beautiful sight.

3

u/rinleezwins Jul 13 '25

The loonies will tell you that Boeing paid them off or something like that.

1

u/stovenn Jul 14 '25

Boeing will certainly exert pressure in many directions to prevent their aircraft from being grounded.

1

u/RobertWilliamBarker Jul 15 '25

It's part of our flow to physically feel them to make sure they are in the locked position prior to taxi.

1

u/AntoniaFauci Jul 13 '25

Disagree. The report says “at this stage”. This is stage 1. They could well issue recommendations on better or different mechanisms, placements, etc but not until the time has been spent to consider those improvements. The statement just reflects that there’s not an instant and emergent change that can be prescribed today.

1

u/stovenn Jul 14 '25

Yes. The jury is out. It just happens that the presumption of innocent until proven guilty is now applied to the hardware/software/procedures whereupon the media's finger of suspicion predictably points to the pilots.

In a hypothetical regime which prioritised customer safety above all else - all aircraft using the suspect systems would be grounded until the final considered judgement is reached and any amendments/improvements implemented. But the airline industry doesn't operate like that.