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T28B
2025-06-21T17:45:00 permalink Post: 11907933 |
Not
confirmed
. What is apparent is a (substantial) loss of thrust. That's what one can say with some certainty.
if so, why weren't people commenting on this from the videos of the incident (if the audio was good enough to detect the RAT then surely it was good enough to tell whether the engines were running).
Thank you for your patience!
2 users liked this post. |
PBL
2025-06-22T12:43:00 permalink Post: 11908512 |
The "bigger issue", as you put it, is Boeing company organisational and engineering effectiveness. In this accident, so far, we are looking at (at least) two nominally independent phenomena that inhibited continued safe flight, and nobody has a clue yet (or maybe the investigation team does) how those phenomena can possibly have come to be. This singular, so far inexplicable, event occurred with an aircraft with over a decade and 30 million hours of use and no previous fatal accidents. Compare that with the A320, which had 5 fatal accidents in its first decade. The Boeing 777 had one (a refuelling incident in Denver in which the fuel operator died). Boeing organisational behaviour has been the subject of two scholarly books, one extensive US Congressional report, and a lot more (most recently since January 2025). There is a lot of information, even very interesting information. What there is not in any of that information (I ask you to take my word for it) is any indication of why two working engines simultaneously suffered serious reduction of thrust shortly after unstick. That is a different topic entirely. And in my opinion it is the topic which belongs in this thread. Last edited by PBL; 22nd Jun 2025 at 13:42 . Reason: Brain bit flip: said "miles", obviously meant "hours". Duuh 5 users liked this post. |
MaybeItIs
2025-06-22T23:35:00 permalink Post: 11908907 |
That\x92s the nature of a common mode bug. If the software was vulnerable to Mars being in the house of Uranus, the scent of lilacs and the DOW being less than 42,000 then you\x92d expect the failure to occur everywhere when these conjoined. Same when an aeroplane\x92s systems and/or the environment present data that triggers an unplanned/unforeseen response in something like an EEC/FADEC. The experts still appear to think that this is unlikely but we have been presented with an unlikely occurrence...
Yes, there may be (let's assume is) "identical" FADEC/TCMA hardware and firmware on both engines, but if the Left Engine is subject to Mars in the house of Uranus (wink wink), then the Right Engine cannot be, maybe it's Venus in the same House. This is simply because the Left engine TCMA 'contraption', I'm going to call it, is monitoring Left Engine Conditions (Shaft Speed, T/L setting / position data - Right or Wrong, and calculating and comparing accordingly against its internal map) while the opposite TCMA "device" is monitoring and calculating etc, Right Engine Conditions. There are some things in common, but (I say) it's virtually impossible for the Engine Conditions being individually monitored to be identical in both engines. The Thrust Levers are electro-mechanical devices, almost certainly at this stage pushed by a somewhat squishy human hand, likely with a slight offset. What is the probability that those two levers are in identical positions, and even if they are, that the calibration (e.g. "zero points") of both levers are identical, and that the values they output (response slopes/curves) are exactly matching in every matching point in their individual travels? That's just one aspect, but consider the engines. They are different ages. Have different amounts of wear. They have separate fuel metering valves (or other names), separate HP Fuel pumps (and, I guess relief valves?), all also subject to wear), and each has a host of other, correspondingly paired, sensors, (maybe of different makes and certainly of different ages and different calibrations and response curves) from which each FADEC, supposedly independently of the TCMA, adjusts the fuel metering device settings and resulting engine power, and shaft RPMs follow in some other slightly non-matching way. Sure, I would completely agree that the two engines and their calculated Throttle Lever positions to Shaft RPMs are always going to be similar during normal, matched operation, and they will very likely dance with each other, maybe one 'always' (75% of the time, say) leading during one dance (TO, say) with the other leading in dancing to a different tune (descent, say). To me, the fact that this appears to have been an almost simultaneous dual engine failure, pretty much, for me, rules out a FADEC/TCMA firmware bug, especially as there don't seem to be any reports of even a single engine mid-air TCMA shutdown. HOWEVER, and I want to stress this, that doesn't rule out the possibility that both TCMAs shutdown their respective engines simultaneously. Any lack of simultaneity observed would be due to those slight differences in other pieces of hardware, such as the time for one Shutoff valve to close versus the other. As far as I know, there isn't enough information on what's actually inside those TCMA Black Boxes to say anything for sure, but here's a thought, which I think has been alluded to, or the question asked, here in one or other thread, earlier. What does the TCMA firmware do when an engine is already running at a high power setting and TWO things occur in quick succession? I suspect this kind of event is a highly probable cause, but these two events have not occurred close enough together, or ever, before. Imagine this: Plane taking off, Throttle Levers near Full Power, Engines performing correctly, also near Full Power, Rotation etc all normal, plane beginning to climb, positive rate achieved. Pilot calls GEARUP. GearUp, activated. The Gear Retract sequence begins. Due to some unforeseen or freshly occurring (maybe intermittent short or open circuit) linkage between the gear Up sequence and the WOW or Air/Ground System, the signal to both TCMAs suddenly switches to GROUND. All "good", so far, as the engine RPMs match the Throttle Lever settings and TCMA doesn't flinch. The plane could be in a Valid Takeoff sequence, so it had better not! But it does make a bit of sense. How is WOW / Air/Ground detected? Somewhere near the Landing Gear, I assume. HOWEVER, now, a moment later, and perhaps due to a related system response, the Thrust Levers suddenly get pulled back to Idle, whether by man or Machine. What would you expect the TCMA system to do? I would guess, fairly soon thereafter, two, independent, Fuel Cutoffs... Though I fully admit, I'm guessing based on a severe lack of knowledge of that Firmware. Ok, no need for further explanation on that point, but I did refer to TCMA unflatteringly as a contraption, earlier. Last night (regrettably, before bed) I started looking at the TCMA Google Patent. Let's just say, so far, I'm aghast! My first impressions are bad ones. How did this patent even get approved? What I suspect here, now, is not a Firmware bug, but a serious Logic and Program Defect. But we'd have to see what's inside the firmware. When I get more time, I'll dig deeper. 1 user liked this post. |
TURIN
2025-06-29T10:48:00 permalink Post: 11912945 |
Can anyone suggest a good reason why the captain should issue a Mayday call at that point? The crew should have been extremely busy with the situation. Aviate, Navigate, Communicate is a mantra we are all familiar with. So why communicate?
Having discussed the accident with experienced pilot colleagues, we have all considered that the Egyptair 990 case offered similarities. Yet this is almost a taboo subject. And one's suspicions are raised by the fact that Air India/Tata are keeping ICAO out of the post-crash investigation. Incidentally, I sincerely hope that we are wrong about the possibility of a deliberate dual engine shutdown shortly after rotation. 4 users liked this post. |
Sailvi767
2025-06-29T14:02:00 permalink Post: 11913050 |
I see nothing in the video’s to suggest the aircraft was out of control. It was gliding almost exactly as you can expect from an event starting with the gear down and flaps at 5. As the aircraft nears the ground it appears there is a bit of flare to break the rate of descent. That is exactly what you would expect the pilots to do and their only course of action with a dual engine failure at low altitude.
4 users liked this post. |
The Brigadier
2025-06-30T08:28:00 permalink Post: 11913431 |
We know that the right-hand GEnx-1B was removed for overhaul and re-installed in March 2025 so it was at \x93zero time\x94 and zero cycles, meaning a performance asymmetry that the FADEC would have to manage every time maximum thrust is selected. If the old engine was still on the pre-2021 EEC build while the fresh engine carried the post-Service Bulletin software/hardware, a dual \x93commanded rollback\x94 is plausible. A latent fault on one channel with the mid-life core can prompt the other engine to match thrust to maintain symmetry, leading to dual rollback.
Last edited by The Brigadier; 30th Jun 2025 at 11:43 . 3 users liked this post. |
skwdenyer
2025-06-30T12:29:00 permalink Post: 11913592 |
We know that the right-hand GEnx-1B was removed for overhaul and re-installed in March 2025 so it was at \x93zero time\x94 and zero cycles, meaning a performance asymmetry that the FADEC would have to manage every time maximum thrust is selected. If the old engine was still on the pre-2021 EEC build while the fresh engine carried the post-Service Bulletin software/hardware, a dual \x93commanded rollback\x94 is plausible. A latent fault on one channel with the mid-life core can prompt the other engine to match thrust to maintain symmetry, leading to dual rollback.
1 user liked this post. |
silverelise
2025-06-30T13:05:00 permalink Post: 11913609 |
India's Minister of State for Civil Aviation appears to be confirming in this
this interview
that the cause of the accident was a dual engine failure. Which is, I think, the first vaguely official confirmation of what happened that has been released? He also confirmed that all the data from the recorders has been downloaded and is being processed by the Indian AAIB, no boxes have been sent abroad.
The 30 day deadline for the preliminary report is July 12th. 1 user liked this post. |
Lonewolf_50
2025-06-30T13:08:00 permalink Post: 11913613 |
We know that the right-hand GEnx-1B was removed for overhaul and re-installed in March 2025 so it was at “zero time” and zero cycles, meaning a performance asymmetry that the FADEC would have to manage every time maximum thrust is selected. If the old engine was still on the pre-2021 EEC build while the fresh engine carried the post-Service Bulletin software/hardware, a dual “commanded rollback” is plausible.
A latent fault on one channel with the mid-life core can prompt the other engine to match thrust to maintain symmetry, leading to dual rollback. ![]()
Originally Posted by
silverelise
He also confirmed that all the data from the recorders has been downloaded and is being processed by the Indian AAIB,
no boxes have been sent abroad.
The 30 day deadline for the preliminary report is July 12th.
Originally Posted by
the linked article
Investigators still haven’t ruled out the possibility of sabotage being behind the Air India crash in
Ahmedabad
earlier this month that
killed 274 people
, according to India’s aviation minister. The Aircraft Accident Investigation Bureau (AAIB) has confirmed that the aircraft’s flight recorders – known as black boxes – will not be sent outside the country for assessment and will be analysed by the agency, said Murlidhar Mohol, the minister of state for civil aviation.l
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adfad
2025-06-30T15:49:00 permalink Post: 11913716 |
India's Minister of State for Civil Aviation appears to be confirming in this interview that the cause of the accident was a dual engine failure. Which is, I think, the first vaguely official confirmation of what happened that has been released? He also confirmed that all the data from the recorders has been downloaded and is being processed by the Indian AAIB, no boxes have been sent abroad.
The 30 day deadline for the preliminary report is July 12th.
The minister called the crash a \x93rare case\x94 and, referring to claims by veteran pilots and experts that a dual-engine failure may have led to the crash, said: \x93It has never happened that both engines have shut down together.\x94 \x93Once the report comes, we will be able to ascertain if it was an engine problem or fuel supply issue or why both engines had stopped functioning.
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fdr
2025-06-30T23:39:00 permalink Post: 11913950 |
We know that the right-hand GEnx-1B was removed for overhaul and re-installed in March 2025 so it was at \x93zero time\x94 and zero cycles, meaning a performance asymmetry that the FADEC would have to manage every time maximum thrust is selected. If the old engine was still on the pre-2021 EEC build while the fresh engine carried the post-Service Bulletin software/hardware, a dual \x93commanded rollback\x94 is plausible. A latent fault on one channel with the mid-life core can prompt the other engine to match thrust to maintain symmetry, leading to dual rollback.
3 users liked this post. |
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