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Engineless
June 15, 2025, 17:15:00 GMT permalink Post: 11902643 |
I think it needs to be said again that pretty much anything can happen to the aircraft systems and the engines will carry on running - this is by design as they have independent FADEC and power supplies and at sea level fuel will get through without boost pumps. You could almost saw the wing off the fuselage and the engine would still produce thrust, TCMA notwithstanding.
We don\x92t know yet what actually triggered the RAT from the relatively short list but every item on it means there is a serious/critical failure(s). The flight path suggests that it was a double engine failure or shutdown (commanded or uncommanded) as anything else should have left the aeroplane in a poor state but able to climb away . Secondly, as a (now ex) glider pilot who remains extremely interested in aviation in most of its forms, this discussion has been an education and thought-provoking, as it so frequently is whenever I lurk here (usually without logging in). Thank you all for sharing your knowledge, expertise and thoughts. To my mind the above post (especially the sentence I highlighted) is amongst the best (and most succinct) summary of what the pilots likely faced, with little to no time to resolve the situation. I cannot imagine those last few seconds and my heart goes out to them, the passengers and the many loved ones left behind. If there is any good that can come of this, it is that the cause is found quickly, with no bias, and steps are taken to ensure the same holes in the cheese cannot happen again. Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Dual Engine Failure Engine Failure (All) FADEC Fuel (All) RAT (All) Thread Moderation |
Engineless
July 11, 2025, 20:26:00 GMT permalink Post: 11919763 |
Preliminary Air India crash report published
Last edited by Saab Dastard; 11th July 2025 at 21:40 . Reason: Fixed link Subjects (links are to this post in the relevant subject page so that this post can be seen in context): AAIB (All) Preliminary Report |
Engineless
July 11, 2025, 20:40:00 GMT permalink Post: 11919772 |
The aircraft achieved the maximum recorded airspeed of 180 Knots IAS at about 08:08:42
UTC and immediately thereafter, the Engine 1 and Engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position one after another with a time gap of 01 sec. The Engine N1 and N2 began to decrease from their take-off values as the fuel supply to the engines was cut off. In the cockpit voice recording, one of the pilots is heard asking the other why did he cutoff. The other pilot responded that he did not do so. The CCTV footage obtained from the airport showed Ram Air Turbine (RAT) getting deployed during the initial climb immediately after lift-off (fig. 15). No significant bird activity is observed in the vicinity of the flight path. The aircraft started to lose altitude before crossing the airport perimeter wall. As per the EAFR, the Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN at about 08:08:52 UTC. The APU Inlet Door began opening at about 08:08:54 UTC, consistent with the APU Auto Start logic. Thereafter at 08:08:56 UTC the Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN. When fuel control switches are moved from CUTOFF to RUN while the aircraft is inflight, each engines full authority dual engine control (FADEC) automatically manages a relight and thrust recovery sequence of ignition and fuel introduction. The EGT was observed to be rising for both engines indicating relight. Engine 1’s core deceleration stopped, reversed and started to progress to recovery. Engine 2 was able to relight but could not arrest core speed deceleration and re-introduced fuel repeatedly to increase core speed acceleration and recovery. The EAFR recording stopped at 08:09:11 UTC As per the EAFR data both engines N2 values passed below minimum idle speed, and the RAT hydraulic pump began supplying hydraulic power at about 08:08:47 UTC. RAT in extended position 15 As per the EAFR, the Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN at about 08:08:52 UTC. The APU Inlet Door began opening at about 08:08:54 UTC, consistent with the APU Auto Start logic. Thereafter at 08:08:56 UTC the Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN. When fuel control switches are moved from CUTOFF to RUN while the aircraft is inflight, each engines full authority dual engine control (FADEC) automatically manages a relight and thrust recovery sequence of ignition and fuel introduction. The EGT was observed to be rising for both engines indicating relight. Engine 1’s core deceleration stopped, reversed and started to progress to recovery. Engine 2 was able to relight but could not arrest core speed deceleration and re-introduced fuel repeatedly to increase core speed acceleration and recovery. The EAFR recording stopped at 08:09:11 UTC At about 08:09:05 UTC, one of the pilots transmitted “MAYDAY MAYDAY MAYDAY”. 08:08:42 Engine 1 and Engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position. One of the pilots asks the other why did he cutoff. The other pilot responded that he did not do so. 08:08:52 Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN 08:08:56 Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN Who (or what?) operated the cutoff switches? Last edited by Engineless; 11th July 2025 at 20:53 . Subjects (links are to this post in the relevant subject page so that this post can be seen in context): APU CCTV EAFR FADEC Fuel (All) Fuel Cutoff Fuel Cutoff Switches Hydraulic Failure (All) MAYDAY Pilot "Why did you cut off" Preliminary Report RAT (All) RAT (Deployment) RUN/CUTOFF Relight Timeline (Preliminary Report) |
Engineless
July 11, 2025, 21:51:00 GMT permalink Post: 11919857 |
The phrase in the report is "switches transitioned from RUN to CUTOFF position".
Does the FDR actually have some input of the physical position of the switches or is it just measuring the output signal voltage which might be changed by a momentary short from liquid or swarf. Both signals go to cutoff within 1 second but then one recovers four seconds after the other. Surely a pilot discovering a turned off switch would have both back on in less than four seconds. Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FDR Fuel (All) Fuel Cutoff Switches RUN/CUTOFF |
Engineless
July 11, 2025, 22:07:00 GMT permalink Post: 11919881 |
A douple-pole switch. One pole used for FDR signal for the physcial switch position. The other pole for the electrical switching circuit.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Cockpit Area Audio FDR Fuel (All) Fuel Cutoff Switches |
Engineless
July 12, 2025, 20:34:00 GMT permalink Post: 11920817 |
The accident report indicates that the aircraft had a STAB master caution warning on the previous sector. A maintenance action took place during the turnaround in AMD before the accident flight.
Noting that the two guarded stab cutoff switches are directly adjacent to the two guardedfuel run/cutoff switches at the base of the throttle quadrant ,
Since some posters seem focused on the theory that the fuel control switches didn't move - just the electric output did (and as I posted earlier, the FDR only knows electrical states, there is literally no other way for the FDR to monitor the switch position).
So I did a little thought experiment. Uncommanded engine shutdowns (for all causes) are already rare - a 10-6 event. Now, during my 40 year career, I can't remember ever encountering a case where the fuel shutoff was commanded without a corresponding movement of the fuel switch. However in this industry it's a good idea to 'never say never', so let's assume it's happened. It would take something like a hot short to cause it to happen ( moving the voltage from RUN to CUTOFF ) since an open circuit will simply leave the valves where they were. That would put its probability way out there - something like 10-8/hr.
In the cockpit voice recording, one of the pilots is heard asking the other why did he cutoff.
The other pilot responded that he did not do so I would suggest starting with the maintenence engineer/crew who found 'no fault' after the STAB master caution was investigated immediately prior to this tragic flight. It would not be the first time that 'maintenance' caused an incident... Also, I urge you all to consider how many accidents have been blamed on 'pilot error' (how convenient when billion-dollar companies are at risk) only for further information to come to light that then exonerates the pilots (these stories don't usually make the front page). Try to stay open-minded folks. The investigation has a very long way to go. Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FDR Fuel (All) Fuel Cutoff Fuel Cutoff Switches Pilot "Why did you cut off" RUN/CUTOFF Switch Guards |
Engineless
July 12, 2025, 21:42:00 GMT permalink Post: 11920857 |
Like I said,
if you take the preliminary report version of cockpit dialog at face value
, then if the fuel cutoff toggles were never physically turned off maybe they were not physically turned back on. Immediately prior to this flight the pilots reported a STAB master caution, which was investigated but 'no fault' was found. Intermittent electrical fault? Software/logic problem? Stranger things have happened. At least one maintenance engineer would have been in the cockpit immediately prior to this flight. The actions taken by this person(s) should also be part of the investigation.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Electrical Failure Fuel (All) Fuel Cutoff Fuel Cutoff Switches Preliminary Report |
Engineless
July 12, 2025, 21:50:00 GMT permalink Post: 11920866 |
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All) Fuel Cutoff Switches |
Engineless
July 15, 2025, 17:02:00 GMT permalink Post: 11923088 |
After all the analysis on PPRuNE, fuel switch failure (well, dual switch failure, at practically the same time) seems so unlikely it's no longer worthy of consideration. However, I'm still open to the idea of a failure elsewhere that may have signalled the fuel switches had transistioned from Run to Cutoff wthout physical movement of either switch. Why? Firstly, because of this (taken from the preliminary report)
The crew of the previous flight (AI423) had made Pilot Defect Report (PDR) entry for status
message “STAB POS XDCR” in the Tech Log. The troubleshooting was carried out as per FIM by Air India’s on duty AME, and the aircraft was released for flight at 0640 UTC. ![]() The STAB cutout switches are located next to the Fuel cutoff switches. What did Air India’s on duty AME do as part of their troubleshooting? Were panels removed to gain access to the rear of the switches and wiring? What about wiring and data connections elsewhere? What may have been disconnected/disturbed as part of this process? Do the STAB cutout switches and Fuel cutoff switches share any connectors that could have been inadvertantly cross-connected? Etc. It would not be the first time that an engineer had innocently done something that later caused an accident. And I haven't read anything about possible nefarious action by a (disgruntled?) engineer - but I've seen lots of accusations directed at the pilot(s)... Secondly, the preliminary report's version of (part of) the conversation in the cockpit -
In the cockpit voice recording, one of the pilots is heard asking the other why did he cutoff.
The other pilot responded that he did not do so. A) one of the pilots lied B) one of the pilots attempted to deflect blame onto the other pilot for the benefit of the CVR C) One of the pilots unknowingly operated the fuel cutoff switches. D) One of the pilots deliberately operated the fuel cutoff switches. It is all too easy to blame one of the pilots when in reality no one outside of the official investigation may yet know what most likely happened. Subjects (links are to this post in the relevant subject page so that this post can be seen in context): CVR Fuel (All) Fuel Cutoff Fuel Cutoff Switches Pilot "Why did you cut off" Preliminary Report |
Engineless
July 15, 2025, 17:56:00 GMT permalink Post: 11923129 |
Googling, inspired by the mention in the
PR
about a MEL on the \x91core network\x92, I came across the polemics between Boeing and IOActive a few years ago about the vulnerability of 787 core systems to outside interference (hacker attack), including the FCO module. It\x92s definitely not my specialty, but I thought to flag it in case someone has more informed ideas about this. To my mind it could potentially \x93outshine\x94 intentional crew action. Boeing at the time denied such options, of course. Obviously also in good faith, but who knows where we are 6 years on.
https://www.wired.com/story/boeing-7...ecurity-flaws/ From the article:
Now, nearly a year later, Santamarta claims that leaked code has led him to something unprecedented: security flaws in one of the 787 Dreamliner's components, deep in the plane's multi-tiered network. He suggests that for a hacker, exploiting those bugs could represent one step in a multi!stage attack that starts in the plane\x92s in-flight entertainment system and extends to highly protected, safety-critical systems like flight controls and sensors.
Subjects (links are to this post in the relevant subject page so that this post can be seen in context): MEL |
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