2025-06-15T13:54:00
permalink Post: 11902489
There's some possible fuel contamination mechanisms which would only affect one aircraft
- The fuel truck\x92s water-absorbing \x93monitor\x94 element breaks up, the first aircraft after the break gets the bead slug; later uplifts may be clear once the hose is flushed. The beads jam metering valves almost immediately.
- After pipe maintenance, the first few hundred litres can carry residual cleaning surfactant that strips protective films and causes filter-monitor \x93soap lock\x94.
- Biofilm growth happens inside one aircraft\x92s wing tanks when it sits in humid conditions or does short hops with warm fuel. On the next flight the biofilm shears off, blocks strainers,
- The fuel truck\x92s water-absorbing \x93monitor\x94 element breaks up, the first aircraft after the break gets the bead slug; later uplifts may be clear once the hose is flushed. The beads jam metering valves almost immediately.
- After pipe maintenance, the first few hundred litres can carry residual cleaning surfactant that strips protective films and causes filter-monitor \x93soap lock\x94.
- Biofilm growth happens inside one aircraft\x92s wing tanks when it sits in humid conditions or does short hops with warm fuel. On the next flight the biofilm shears off, blocks strainers,
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2025-06-16T08:51:00
permalink Post: 11903270
If TCMA cut fuel flow while still on the runway the aircraft would have been decelerating from the moment it lifted off, which is not what the ADS-B data indicates. The kinetic energy in the rotating parts of the engine wouldn't add much speed to the aircraft as the engines run down with no more energy being added via fuel.
In no particular order, here are some more thoughts on TCMA having caught up on the thread:
If you cut the fuel from two big engines at take-off power, there must be some delay before n2 decays below the threshold for generation (below idle n2), the generators disconnect and RAT deploys. GEnx have relatively long spool up/down times as the fan is so large (and would be exposed to 170+kts of ram air). Perhaps someone has a view on how long this would be, but I imagine it could easily be 10s or more between fuel cut off and RAT deployment. On AI171 the RAT appears to be already deployed at the beginning of the bystander video. That starts c. 13s before impact and around 17s after rotation. This does not prove anything except that the supposed shut down must have happened very close to rotation and could have happened just before rotation while the a/c was on the ground.
As a thought experiment, imagine if ANA985 in 2019 had decided to go around. The a/c rotates and is ~50 ft above the runway, suddenly both engines spooling down, very little runway left to land on and no reverse thrust available. I am struck by how similar this scenario is to AI171. This theory would require there to have been unexpected thrust lever movement in the moments before rotation - but plausibly one pilot moving to reject, followed by an overrule or change of heart - or even a simple human error such as the recent BA incident at LGW - could achieve this. This is perhaps more likely that any sensor fault that you would expect to only impact a single engine given the redundancy of systems.
Tdracer writes that a key requirement of TCMA is to identify an engine runaway in the event of an RTO, in order to allow the a/c to stop on the runway. This will have been tested extensively - it is a big leap to imagine a false activation could be triggered. It did happen on ANA985 but through a very unusual set of inputs including application of reverse (albeit this latter point may not be relevant if TCMA logic does not distinguish between the reverser being deployed or not).
Incidentally there is an assumption the TCMA software version in place on the ANA flight had already been patched and fixed on AI171. That probably is the case but I am not sure it is a known fact.
In summary I remain baffled by this tragic accident. I have not yet read anything that explicitly rules out TCMA activation and it remains a possibility due to the vanishingly small number of factors that could shut down two engines at apparently the exact same moment when they have fully redundant systems. Fuel contamination, for example, has typically impacted each engine a few minutes (at least) apart. I am also cautious (as others have pointed out) of a form of confirmation bias about Boeing software systems with four-letter acronyms.
In my mind the cause could equally well be something completely different to anything suggested on this thread, that will only become clear with more evidence. All of the above also incorporates a number of theories, i.e. that there was an engine shutdown - that are not conclusively known.
Thank you to the mods for an excellent job.
3 users liked this post.
2025-06-14T08:43:00
permalink Post: 11903718
I’m not a 787 driver so for fear of looking dumb in front of those that are this still confuses me. Even IF they’ve mis-selected the flap setting (I still don’t think it’s been cemented on here that there is in fact a FMS/flap setting disagreement warning but i believe there is), had the wrong de-rated take off settings, selected flaps instead of gear up the 787 with massive high bypass engines, FBW and full envelope protections surely cannot let itself be put in such a low energy/high alpha regime as we saw in the videos IF it has both fans functioning normally, surely?
the pilots may have messed up royally and numerous times so those holes lined up but the plane is the final block in the chain and a 21st century all digital entirely clean sheet design was sold as being immune to such catastrophic outcomes from a few minor (consequential yes) and fairly common errors- aren’t all the protections and our procedures designed after decades of mistakes?
im having a hard time squaring how a fully functioning modern bird like this could allow for this outcome and almost whatever the pilots did outside of unbelievable inputs and the pilots are are a bit of a red herring IMO
Dale Winsley
@Winsleydale
No. The LE slats are deployed therefore the flaps are as well. This is an automatic linkage. The flaps are set at Take-Off. Hard to see from the angle but they are...if slats are out (easy to see) then flaps are set. Looks like Flaps 5. Also, the 787 has the highest Thrust-to-Weight ratio of any airliner on Earth. The change in Alpha and lift is a trifling matter for it, at these settings (1-5). It will fly out of it easily, even at that density altitude. The attitude change is - in the circumstances I describe, consistent with a massive power loss (both sides). I believe based on probability that simultaneous mechanical failure is not the cause. Fuel contamination or starvation is likewise unlikely based on the 787 fuel system. The common element is the FADEC/Autothrottle/TOGO. However, each engine FADEC is dual redundant two channels. So any such common failure must happen further upstream. From a design perspective, that would be unthinkable. But this is Boeing. Given what I can see with my own eyes, I believe the flap issue is a non-starter. Also, re the landing gear: Clearly the Positive Rate challenge would be met based on normal rotation and fly-off at V2. But since we know the flaps were set correctly, that rules out an "oopsie" moment. Just as likely there was at the challenge moment an indication that something was amiss, and the Gear Up call was not made. They see both N1s unwinding and it takes a second to get past the WFT factor. They cross-check and see the airspeed also unwinding. Then they unload the Alpha and pitch to gear down Vy. And they had another 6 seconds. Whatever it was, it was not a flap, mechanical or fuel issue. We will know soon enough. But this is Boeing. My gut says "software". All 787s worldwide need to be grounded, now.
6:10 AM \xb7 Jun 14, 2025
\xb7
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2025-06-16T08:51:00
permalink Post: 11903752
If TCMA cut fuel flow while still on the runway the aircraft would have been decelerating from the moment it lifted off, which is not what the ADS-B data indicates. The kinetic energy in the rotating parts of the engine wouldn't add much speed to the aircraft as the engines run down with no more energy being added via fuel.
In no particular order, here are some more thoughts on TCMA having caught up on the thread:
If you cut the fuel from two big engines at take-off power, there must be some delay before n2 decays below the threshold for generation (below idle n2), the generators disconnect and RAT deploys. GEnx have relatively long spool up/down times as the fan is so large (and would be exposed to 170+kts of ram air). Perhaps someone has a view on how long this would be, but I imagine it could easily be 10s or more between fuel cut off and RAT deployment. On AI171 the RAT appears to be already deployed at the beginning of the bystander video. That starts c. 13s before impact and around 17s after rotation. This does not prove anything except that the supposed shut down must have happened very close to rotation and could have happened just before rotation while the a/c was on the ground.
As a thought experiment, imagine if ANA985 in 2019 had decided to go around. The a/c rotates and is ~50 ft above the runway, suddenly both engines spooling down, very little runway left to land on and no reverse thrust available. I am struck by how similar this scenario is to AI171. This theory would require there to have been unexpected thrust lever movement in the moments before rotation - but plausibly one pilot moving to reject, followed by an overrule or change of heart - or even a simple human error such as the recent BA incident at LGW - could achieve this. This is perhaps more likely that any sensor fault that you would expect to only impact a single engine given the redundancy of systems.
Tdracer writes that a key requirement of TCMA is to identify an engine runaway in the event of an RTO, in order to allow the a/c to stop on the runway. This will have been tested extensively - it is a big leap to imagine a false activation could be triggered. It did happen on ANA985 but through a very unusual set of inputs including application of reverse (albeit this latter point may not be relevant if TCMA logic does not distinguish between the reverser being deployed or not).
Incidentally there is an assumption the TCMA software version in place on the ANA flight had already been patched and fixed on AI171. That probably is the case but I am not sure it is a known fact.
In summary I remain baffled by this tragic accident. I have not yet read anything that explicitly rules out TCMA activation and it remains a possibility due to the vanishingly small number of factors that could shut down two engines at apparently the exact same moment when they have fully redundant systems. Fuel contamination, for example, has typically impacted each engine a few minutes (at least) apart. I am also cautious (as others have pointed out) of a form of confirmation bias about Boeing software systems with four-letter acronyms.
In my mind the cause could equally well be something completely different to anything suggested on this thread, that will only become clear with more evidence. All of the above also incorporates a number of theories, i.e. that there was an engine shutdown - that are not conclusively known.
Thank you to the mods for an excellent job.
1 user liked this post.
2025-06-17T03:34:00
permalink Post: 11903942
Hopefully the route cause will be found, and I would not be surprised one bit if it is something totally left field that no one had considered, simple or complex.
3 users liked this post.
2025-06-17T16:23:00
permalink Post: 11904442
As more days pass without the FAA/EASA issuing an emergency Airworthiness Directive re. the 787 Dreamliner, it does appear more likely the cause of the crash was specific to the Air India aircraft (as per speculation on fuel contamination, bad maintenance, crew error etc. etc.)
2 users liked this post.
2025-06-17T18:04:00
permalink Post: 11904524
As more days pass without the FAA/EASA issuing an emergency Airworthiness Directive re. the 787 Dreamliner, it does appear more likely the cause of the crash was specific to the Air India aircraft (as per speculation on fuel contamination, bad maintenance, crew error etc. etc.)
If the data is readable there may be a lot of politics and reputation on how that data may be interpreted. Behind the veneer of international cooperation vested interests will be being considered, advocated and agreed.
It, unfortunately, is naive to think that politics will not have a silent presence in agreeing a press release. Boeing and GE are flagship USA companies. Air India is the flagship carrier of India.
Investigations of all types first establish what happened, then how and why, before recommendations and actions. There is a possibility that they know the what, but the how and why incur liability.
5 users liked this post.
2025-06-17T18:54:00
permalink Post: 11904568
One would hope, but, whilst there has been confirmation that the EAFRs have been recovered, nothing has been reported about their state or whether they have been downloaded or examined.
If the data is readable there may be a lot of politics and reputation on how that data may be interpreted. Behind the veneer of international cooperation vested interests will be being considered, advocated and agreed.
It, unfortunately, is naive to think that politics will not have a silent presence in agreeing a press release. Boeing and GE are flagship USA companies. Air India is the flagship carrier of India.
Investigations of all types first establish what happened, then how and why, before recommendations and actions. There is a possibility that they know the what, but the how and why incur liability.
If the data is readable there may be a lot of politics and reputation on how that data may be interpreted. Behind the veneer of international cooperation vested interests will be being considered, advocated and agreed.
It, unfortunately, is naive to think that politics will not have a silent presence in agreeing a press release. Boeing and GE are flagship USA companies. Air India is the flagship carrier of India.
Investigations of all types first establish what happened, then how and why, before recommendations and actions. There is a possibility that they know the what, but the how and why incur liability.
Investigators will try to establish a single source or truth. For them, that\x92s an ideal outcome. But due to the nature of investigations, the aim gets derailed as established facts versus possible/potential scenarios based on missing links of the chain are pieced together. But for sure, commercial considerations and liability wont enter into a proper investigation. The task of the investigators is to determine the how and why.
Theres a saying, and it may even have been the title of a book\x85 Lift is a gift but Thrust is a must. In this case, certainly one or both were absent.
For 2 (maybe 3 if it was a training flight) professional people, the day started with waking up, getting ready, saying goodbye to loved ones, who they believed they would see again soon in 2-3 days. Sadly, that won\x92t happen, and it\x92s the job of the investigators to find out why and liability isn\x92t a hindrance to them.
They will look at every piece of evidence and recreate the events. But it will take time.
information worthy of note is:
A) The gear was still down.
B) It would appear (due to some work by amazing members) that the RAT was indeed deployed.
Other observances:
1. Bits flying off the aircraft. (From experience of operating in this area, they like to fly kites, and waste thermals and floats around, notably plastic bags) I have no idea if that la what we see or not.
2. Generally in India, they love using their horns. So whilst you can compare the frequencies of a potential RAT to a motorbike, appreciate there would be a million horns going off too.
3. Some posters have spoken of the \x93startle effect\x94 like they know what they are talking about. The most startling effect of a professional flight deck during an emergency is how calm it is. There aren\x92t hands flying around everywhere. In fact:
V1 > Rotate > Positive Rate > Gear Up > Confirm FD/AP Modes is adjusted to:
V1 > Rotate > Positive Rate > Gear Up > Silence the bell (Or your SOP Variation) FD/AP modes and the PF flies the aircraft.
the next step is to identify the problem, agree on it and then perform the actions. That won\x92t happen below 400\x92.
4. There\x92s no company in the world where Pilots are being fed and watered between V1 and 1000\x92 so spilling drinks on run switches isn\x92t a thing on this departure.
5. Temperature inversion. Yes it\x92s possible and it degrades performance. However, if it\x92s present, it\x92s usually announced on the ATIS. IF other aircraft have reported it.
6. Fuel contamination. Without knowing the systems, yes it\x92s potentially possible, but it would appear no other aircraft have reported being affected by it.
I think, this accident is especially interesting to Professional Aviators and Engineers because I think none of us would ever believe that it could happen. The aircraft is highly automated, the crew have been properly trained and the operation was a regular or possibly training flight.
A query I have is, do later Gen aircraft like the 777/787/747 A330/A350/A380 constantly send Airframe/Engine data home to ops/engineering/oem\x92s. Is it likely the data is out there?
Anyway, I just wanted to post this to reassure the travelling public that Pilots don\x92t try to shut down engines before they raise the gear.
8 users liked this post.
2025-06-18T12:18:00
permalink Post: 11905193
I wonder if the delay in announcing any preliminary findings is because of the enormity of the consequences.
Let us say the investigation team have discovered a unique technical fault that caused the accident, but don’t yet know why it happened, how would the team proceed? On the one hand they’ve uncovered a fault which could reoccur and cause another accident (but a fault that has only happened once in 14 years). On the other hand a grounding would have enormous commercial consequences worldwide, with the possibility that an inspection and/or rectification are not yet available.
What would they do?
Let us say the investigation team have discovered a unique technical fault that caused the accident, but don’t yet know why it happened, how would the team proceed? On the one hand they’ve uncovered a fault which could reoccur and cause another accident (but a fault that has only happened once in 14 years). On the other hand a grounding would have enormous commercial consequences worldwide, with the possibility that an inspection and/or rectification are not yet available.
What would they do?
As I said in a previous post, every day that passes without a EAD suggest the cause was was specific to that aircraft (fuel contamination, maintenance failure, crew error - pick you own theory)
Last edited by The Brigadier; 18th Jun 2025 at 12:43 .
1 user liked this post.
2025-06-18T13:12:00
permalink Post: 11905236
Given that there are >1,100 787s in service, you would be losing a significant part of the World\x92s air transport infrastructure if you grounded them. Also, if you\x92re still nowhere near understanding what caused it, how would you \x93unground\x94 the fleet if you don\x92t get answers for some time? It\x92s obviously something rare/unique, given the 14 years of operation without such an accident, so statistics should be on your side if you did nothing until you had more surety as to where the problem(s) lay?
4 users liked this post.
2025-06-18T15:45:00
permalink Post: 11905345
A case in point is the 2013 Boeing 787 battery fires. After two thermal runaways in 52 000 flight-hours, the root cause was still unknown; however, the FAA nevertheless issued Emergency AD 2013-02-51 grounding every 787 until a modification was available. IMHO a risk where the outcome is catastrophic, even very low probability, would trigger the FAA to issue an Emergency Airworthiness Directive as per their policy.
As I said in a previous post, every day that passes without a EAD suggest the cause was was specific to that aircraft (fuel contamination, maintenance failure, crew error - pick you own theory)
As I said in a previous post, every day that passes without a EAD suggest the cause was was specific to that aircraft (fuel contamination, maintenance failure, crew error - pick you own theory)
At this time, the fault or flaw at the root of this accident and how that fault or flaw worked through aircraft components and systems has not been identified publicly. It might not even have been identified .... I'm not convinced that separating "what" from "how and why" as a semantics exercise is enough to conclude the Annex 13 officials know the root cause yet. Maybe they do, maybe not.
And if they do not, then the contrast with the situation where FAA was, it seemed, keeping a close eye on battery issues in particular, is relevant.
3 users liked this post.
2025-06-20T01:15:00
permalink Post: 11906521
User989 thanks for a nice summary
I am at risk of turning into one of those folks who gets their mind locked on one possibility and keeps banging on about it but here goes;
If the authorities determined that the accident aircraft had been treated by maintenance for microbial growth in the fuel tanks within the last week or so, and they suspected that that procedure was carried out in a way that could result in fuel contamination, then that would explain
1/ No other aircraft being affected
2/ No measures taken at the airport
3/ No AD’s from the regulators
4/ No grounding of 787’s
5/ Flight profile
6/ Rat deployment etc etc
I agree with your statement that dual flameout due fuel contamination is very unlikely, but we ARE dealing with something that is very unlikely. I favour the theory because an error in treating the fuel is so predictably human and simple, and a dual engine failure being related to fuel is also a simple and obvious idea, and it satisfies all we know both about the aircraft’s behaviour, and the authorities behaviour post accident.
I posted a report earlier of a 787-8 powered by the same engine type have both engines roll back sub-idle within a minute of each other while airborne due to this, so we know it can happen in theory.
Now……I want to be clear that I’m not saying I think I know what happened, I’m an average Joe with my hands full just flying the line, but I am a bit surprised that the idea of ‘fuel contamination specific to that airframe’ doesn’t get discussed more on this thread.
Thanks again for the clear summary of discussion thus far.
I am at risk of turning into one of those folks who gets their mind locked on one possibility and keeps banging on about it but here goes;
2. Fuel contamination
No other aircraft affected, no measures taken at airport. Simultaneous flameout due to contaminated fuel very unlikely.
No other aircraft affected, no measures taken at airport. Simultaneous flameout due to contaminated fuel very unlikely.
1/ No other aircraft being affected
2/ No measures taken at the airport
3/ No AD’s from the regulators
4/ No grounding of 787’s
5/ Flight profile
6/ Rat deployment etc etc
I agree with your statement that dual flameout due fuel contamination is very unlikely, but we ARE dealing with something that is very unlikely. I favour the theory because an error in treating the fuel is so predictably human and simple, and a dual engine failure being related to fuel is also a simple and obvious idea, and it satisfies all we know both about the aircraft’s behaviour, and the authorities behaviour post accident.
I posted a report earlier of a 787-8 powered by the same engine type have both engines roll back sub-idle within a minute of each other while airborne due to this, so we know it can happen in theory.
Now……I want to be clear that I’m not saying I think I know what happened, I’m an average Joe with my hands full just flying the line, but I am a bit surprised that the idea of ‘fuel contamination specific to that airframe’ doesn’t get discussed more on this thread.
Thanks again for the clear summary of discussion thus far.
6 users liked this post.
2025-06-20T01:43:00
permalink Post: 11906532
User989 thanks for a nice summary
I am at risk of turning into one of those folks who gets their mind locked on one possibility and keeps banging on about it but here goes;
If the authorities determined that the accident aircraft had been treated by maintenance for microbial growth in the fuel tanks within the last week or so, and they suspected that that procedure was carried out in a way that could result in fuel contamination, then that would explain
1/ No other aircraft being affected
2/ No measures taken at the airport
3/ No AD\x92s from the regulators
4/ No grounding of 787\x92s
5/ Flight profile
6/ Rat deployment etc etc
I agree with your statement that dual flameout due fuel contamination is very unlikely, but we ARE dealing with something that is very unlikely. I favour the theory because an error in treating the fuel is so predictably human and simple, and a dual engine failure being related to fuel is also a simple and obvious idea, and it satisfies all we know both about the aircraft\x92s behaviour, and the authorities behaviour post accident.
I posted a report earlier of a 787-8 powered by the same engine type have both engines roll back sub-idle within a minute of each other while airborne due to this, so we know it can happen in theory.
Now\x85\x85I want to be clear that I\x92m not saying I think I know what happened, I\x92m an average Joe with my hands full just flying the line, but I am a bit surprised that the idea of \x91fuel contamination specific to that airframe\x92 doesn\x92t get discussed more on this thread.
Thanks again for the clear summary of discussion thus far.
I am at risk of turning into one of those folks who gets their mind locked on one possibility and keeps banging on about it but here goes;
If the authorities determined that the accident aircraft had been treated by maintenance for microbial growth in the fuel tanks within the last week or so, and they suspected that that procedure was carried out in a way that could result in fuel contamination, then that would explain
1/ No other aircraft being affected
2/ No measures taken at the airport
3/ No AD\x92s from the regulators
4/ No grounding of 787\x92s
5/ Flight profile
6/ Rat deployment etc etc
I agree with your statement that dual flameout due fuel contamination is very unlikely, but we ARE dealing with something that is very unlikely. I favour the theory because an error in treating the fuel is so predictably human and simple, and a dual engine failure being related to fuel is also a simple and obvious idea, and it satisfies all we know both about the aircraft\x92s behaviour, and the authorities behaviour post accident.
I posted a report earlier of a 787-8 powered by the same engine type have both engines roll back sub-idle within a minute of each other while airborne due to this, so we know it can happen in theory.
Now\x85\x85I want to be clear that I\x92m not saying I think I know what happened, I\x92m an average Joe with my hands full just flying the line, but I am a bit surprised that the idea of \x91fuel contamination specific to that airframe\x92 doesn\x92t get discussed more on this thread.
Thanks again for the clear summary of discussion thus far.
Last edited by Pinkman; 20th Jun 2025 at 02:32 .
7 users liked this post.
2025-06-20T05:55:00
permalink Post: 11906614
I'm not suggesting you are wrong wheelsright, my post to you was in response to posts I have made about potential fuel contamination, being removed. A central point of failure is more likely than the simultaneous shutdown by systems on two separate engines at the point at which the aircraft left the ground. If what is being speculated on is possible then all ETOPs approval should be removed and the engine manufacturers told to start again.
2 users liked this post.
2025-06-20T22:41:00
permalink Post: 11907374
The excellent #724 post by user989 really should be seen as the defining statement on what is currently known.
I’d like to add a complimentary test to user989’s logic on TCMA faults.
Regardless of whether the ‘aircraft on ground’ signal was incorrect after rotation it would have been correct during the takeoff roll. IF there was an unrevealed fault in a thrust lever position signal THEN why didn’t TCMA activate during taxiing or the takeoff roll?
Such a fault occurring spontaneously in just the few seconds after rotation is way way down the probability table. Such a fault occurring spontaneously on both separate (think ETOPS) engine control systems is surely vanishingly unlikely.
They may be out there but you’d have to ask if TCMA is implicated where are the lower consequence precursor events in the 787 fleet? These might be spurious TCMA action on one engine or faults with ‘aircraft on ground’ found during maintenance or engines not responding to thrust lever position and so on.
Change Analysis would ask what happened differently in the few seconds after rotation on this flight that separates it from all other 787 takeoffs and why at that particular time ?The interim report will provide some answers until then please let’s confine this thread to fact based technical discussion and debate.
Re-reading this I did briefly consider suggesting engine overshoot of thrust lever positions and FADEC shut down on N1 overspeed but that leaves a lot of WHY and WHY both engines questions so I dismissed it.
I’d like to add a complimentary test to user989’s logic on TCMA faults.
Regardless of whether the ‘aircraft on ground’ signal was incorrect after rotation it would have been correct during the takeoff roll. IF there was an unrevealed fault in a thrust lever position signal THEN why didn’t TCMA activate during taxiing or the takeoff roll?
Such a fault occurring spontaneously in just the few seconds after rotation is way way down the probability table. Such a fault occurring spontaneously on both separate (think ETOPS) engine control systems is surely vanishingly unlikely.
They may be out there but you’d have to ask if TCMA is implicated where are the lower consequence precursor events in the 787 fleet? These might be spurious TCMA action on one engine or faults with ‘aircraft on ground’ found during maintenance or engines not responding to thrust lever position and so on.
Change Analysis would ask what happened differently in the few seconds after rotation on this flight that separates it from all other 787 takeoffs and why at that particular time ?The interim report will provide some answers until then please let’s confine this thread to fact based technical discussion and debate.
Re-reading this I did briefly consider suggesting engine overshoot of thrust lever positions and FADEC shut down on N1 overspeed but that leaves a lot of WHY and WHY both engines questions so I dismissed it.
But I'd posit these points (without making any assertions about the probabilities of the scenarios).
There is a flaw in the logic arising from the categorical assertion that the 'aircraft on ground' signal 'would have been correct' during the take off roll: "Regardless of whether the ‘aircraft on ground’ signal was incorrect after rotation it would have been correct during the takeoff roll. IF there was an unrevealed fault in a thrust lever position signal THEN why didn’t TCMA activate during taxiing or the takeoff roll?"
What IF the 'aircraft on ground' signal into the TCMA systems was INcorrect during taxi and the take off roll, thus disabling the TCMA functionality during that phase of the flight, making no difference in any event because the engines were operating normally in accordance with the thrust lever settings? In that case, any error in, for example, the thrust lever signals and engine signals to the TCMAs would not have had any consequence. Maybe the signal reversed and stayed INcorrect after take-off. Of course, that's why we are all craving to find out from what source/s the TCMAs get the 'on ground/in air' input/s and what other systems use the same source/s.
And I reiterate the point that the TCMA is "just software". I haven't seen anyone dispute the suggestion that the thing 'common' to all 4 channels of the TCMA is 4 copies of software.
In the earlier thread there was a statement about the 'obsession' of some with TCMA. I'm not 'obsessed' with it, but confess a prejudice towards trying to find a cause that is not a result of crew error. I therefore also have an attraction towards fuel contamination, but have difficulty in believing that fuel contamination would result in such a 'clean', immediate and simultaneous reduction in thrust from both engines after they'd operated normally during the take off roll.
1 user liked this post.
2025-06-21T06:13:00
permalink Post: 11907514
Hoover from the generally respected Pilot Debrief channel put up his analysis.
He analyses the point of rotation looking at the airport layout and using the video with the shack showing the aircraft rotate behind it, in that case the aircraft rotates at a reasonably normal place. That being the case what is the "cloud of particles" that appear to the left of the aircraft ?
He discounts electrical failure affecting both engines due 787 design, and fuel contamination due both engines fed from separate tanks unlikely to affect both engines at the same time.
The possibility that one engine failure occurred at a critical point in the take off and that possibly the wrong engine fuel cutoff switch was pulled.
camera angle with shack and suggested point of rotation
whats this..
He analyses the point of rotation looking at the airport layout and using the video with the shack showing the aircraft rotate behind it, in that case the aircraft rotates at a reasonably normal place. That being the case what is the "cloud of particles" that appear to the left of the aircraft ?
He discounts electrical failure affecting both engines due 787 design, and fuel contamination due both engines fed from separate tanks unlikely to affect both engines at the same time.
The possibility that one engine failure occurred at a critical point in the take off and that possibly the wrong engine fuel cutoff switch was pulled.
camera angle with shack and suggested point of rotation
whats this..
1 user liked this post.
2025-06-21T06:36:00
permalink Post: 11907525
Hoover from the generally respected Pilot Debrief channel put up his analysis.
He analyses the point of rotation looking at the airport layout and using the video with the shack showing the aircraft rotate behind it, in that case the aircraft rotates at a reasonably normal place. That being the case what is the "cloud of particles" that appear to the left of the aircraft ?
He discounts electrical failure affecting both engines due 787 design, and fuel contamination due both engines fed from separate tanks unlikely to affect both engines at the same time.
The possibility that one engine failure occurred at a critical point in the take off and that possibly the wrong engine fuel cutoff switch was pulled.
camera angle with shack and suggested point of rotation
whats this..
He analyses the point of rotation looking at the airport layout and using the video with the shack showing the aircraft rotate behind it, in that case the aircraft rotates at a reasonably normal place. That being the case what is the "cloud of particles" that appear to the left of the aircraft ?
He discounts electrical failure affecting both engines due 787 design, and fuel contamination due both engines fed from separate tanks unlikely to affect both engines at the same time.
The possibility that one engine failure occurred at a critical point in the take off and that possibly the wrong engine fuel cutoff switch was pulled.
camera angle with shack and suggested point of rotation
whats this..
I repeat, do NOT post repeats of discussions already had unless there is something of value which may change or enhance previous posts. This is a prime example of a post which should be vetted and dismissed before pressing Submit Reply 🙈
6 users liked this post.
2025-06-21T15:52:00
permalink Post: 11907864
Some assumed numbers about normal biotreatment.
https://www.biobor.com/wp-content/up...ation-IATA.pdf
If we assume 50 tonnes fuel load a 100ppmw biotreatment will be 5kg of biocide total in all tanks.
The GEnx-1B will burn about 4,5kg/s fuel each on a take off run (give or take a bit) so 9kg/s in both donks for about 20s until rotate.
So the total nominal biocide dose could be pumped in about half a second through both engines on take off power if it where not mixed at all and arrives in both engines at the same time.
This gives you an idea that with the nominal amount of biocide dose not much could have happened. If biocide is the source of this dual EFATO than an extreme overdose in addition to wrong application preventing mixture with the fuel had to be the case.
https://www.biobor.com/wp-content/up...ation-IATA.pdf
If we assume 50 tonnes fuel load a 100ppmw biotreatment will be 5kg of biocide total in all tanks.
The GEnx-1B will burn about 4,5kg/s fuel each on a take off run (give or take a bit) so 9kg/s in both donks for about 20s until rotate.
So the total nominal biocide dose could be pumped in about half a second through both engines on take off power if it where not mixed at all and arrives in both engines at the same time.
This gives you an idea that with the nominal amount of biocide dose not much could have happened. If biocide is the source of this dual EFATO than an extreme overdose in addition to wrong application preventing mixture with the fuel had to be the case.
First, the problem involves the valves (notably but not exclusively FMV and FSV), not the combustion of the product:
It is highly probable that Residue primarily composed of magnesium salts accumulated in FMV spool and FSV spool, which meter engine combustion fuel, restricted movement of spools, caused inadequate fuel metering, thereby led to engine rpm oscillation that occurred from the first flight after conducting biocide treatment.
Investigation into similar cases revealed that there were six cases reported in which both engines could not start in twin engine aircraft, and one case each in which all engines could not start in four-engine aircraft and engine thrust could not be adjusted. Any of these cases were presumed to have been caused by concentration ratio of biocide (Kathon FP1.5) that was set at higher values (about 1,000 ppm) than specified ones during biocide treatments.
From the biocide test result, it is probable that Magnesium salts contained in biocide did not dissolve in fuel, but dissolved in water contained in fuel and were accumulated in spools as crystals through the engine fuel system.
These "rpm oscillations", leading to substantial loss of thrust, could as well have occurred simultaneously, and 81 seconds (for the RH engine) is an awfully long time. According to the report, Kathon FP1.5 is not used anymore for biocide treatment, but another contributor ( nachtmusak , who seems to be a petrol specialist) suggested that other products may have similar effects .
Therefore, regarding the case we are discussing at large (thanks again, mods!), I think we shouldn't overlook the hypothesis of fuel contamination by biocide, since it is a single point of failure (among a very limited number of SPoFs) from a system analysis point of view.
2 users liked this post.
2025-06-21T23:11:00
permalink Post: 11908143
I read the whole threads, keeping my hands on the mousewheel so far since I'm not a pilot, just a EE / safety / systems engineer.
The hamsterwheel ist spinning a lot here, and of course it could be anything including some VHDL FPGA code line or a broken RAM cell in a cheap memory bar within the computer it was compiled with. Anything is possible, but to be honest: development processes, if followed, are usually pushing the probability to a level where it becomes pure theory. BOSCH uses FPGA+\xb5C on the brake control box of cars. They sold 100 millions of those, used 4000h each (car lifetime) without error, with less strict development process. Most errors are made on requirement level, not code.
Also, so far there is no evidence I've seen regarding the 'chicken-egg' problem, did the engines fall below idle (fuel, stall...) and this caused an electrical blackout (-> battery, RAT...) or did an EE problem cause the engines to reduce thrust (FADEC, SW bug...). And where is the common cause in all this?
There has to be a systematic error common to both engines, an external failure affecting both or a dependent fault with one affecting the other within seconds. This is the only thing I think everyone agrees here. And I refuse to beleave the external failure or dependent fault was sitting in the cockpit.
I think it is something not common to every aircraft type for the last 50 years.
So I started searching and found a candidate.
I read myself into the EE architecture of this unique 'bleed-less' design and it's megawatt powergrid since this is the part where I may be able to contribute (and I'm most curious about). Generators on the 787 are >250kW instead of <100kW each and there are two per engine instead of just one. In fact, they can go up to 516 kW and shear off the gearbox at >2200Nm (equal to >2 MW, per generator).
https://www.easa.europa.eu/en/downloads/7641/en (page 11)
So while on any other aircraft the generator is more like the dynamo on your bicycle, those generators are massive (x10).
The gearbox is connected to the HP shaft (N2) on the GEnx. I learned from Wikipedia that RR moved this gearbox to the IP shaft on the Trend 1000. And RR is happy that the A330neo Trend 7000 uses bleed air and less load on the gearbox, since this maintains stability on the HP shaft at light load (also Wikipedia).
Those generators are not in phase and frequency sync, or in other words: If you parallel them, they fight each other, it's like a short. They will almost block if this is not handled by the control box if possible (or some melting fuse blows at some point).
787 electrical system - variable frequency generators?
Somehow I find it hard to believe that they are not able to disturb the engines despite that everyone here so far is claiming that there is no way an electrical problem could influence them because FADEC has it's own supply. I read that one is sufficent to start the engine, usually both are used.
In my mind I find lot's of ways this could influence both engines simultanously. If just the BTBs on the 230V grid got some humidity (hot, no AC, water cooling...) and went up in one big arc (I think they made them semiconductor relays, too).
Could those gearboxes and engines handle 4500Nm / almost 5 MW on each HP shaft, applied within a fraction of a second without any problem?
Or if the engines were in a condition not far from compressor stall, one was stalling and 400kW load jumped from one engines generators to the other...
I did some rough estimation and one of the generators could push N2 below idle in a second or less without fuel just with its normal 250kW load (just inertia).
This is one point which is unique to this airplane model, so maybe worth a closer look.
I know that those engines are burning at >100MW at full power, but how fragile in the balance between compressor load and this one turbine stage on the HP shaft / N2, without the inertia of a 2.8 meter fan? This is just out of my background, any thermodynamic expert here?
Of course I also have no insight in SW and communication within the control boxes, how much they are talking to each other, delaying/ramping load redistribution etc. If FADEC recognizes a flameout, could it instantly command the generators to cut the load, even above idle rpm?
I would assume that some fuel contamination, valve blockade, even compressor stall would pop up slower. But such a generator could kick in within milliseconds.
As a safety guy I learned that one tends to look first at things one is familiar with (SW, HW, mechanics, pilot behaviour, maintainance, depending on one's profession) and in the end it's often the interface and dependent faults within which are not carefully considered (e.g. takeoff situation vs. thermodynamics vs. mechanics vs. power generation vs. humidity vs. generator control...) together with transient behaviour. It was the same with MCAS (safety culture vs. pilot training vs. SW design (repeated action) vs. single AOA input vs. bird strike probability close to ground vs. trim loading/blockade vs. stickshaker noise/distraction).
In fact, I was trying to find information on all those systems and directly found slides on how the engines and generators could be simulated and the power grid tested in a HIL (hardware in the loop) environment. My experience from automotive is that such simulated environments are often far from reality and HIL environment programming finished after the product is already at the customer. But of course its far easier and cheaper to apply and test faults there. But then, some programmer programms what he thinks the reaction of the engine would be.
This 'bleed-less' design was some massive change in airplane EE architecture with hugh consequences on the whole airplane design and extremely hard to fully analyze.
I'm just asking questions and hope that we all learn a lot and this was fully considered or just not an issue. It's just an aspect I found worth mentioning and not only spinning the wheel.
PS: I doubt it was TCMA. The air/ground decision is done in a different box, evaluating 5 inputs in a 1/3 and 1/2 decision according to this discussion. This is then safely sent to the FADEC (as one input) and combined with the thrust lever position and N2. But if the thrust lever position is sensed (redundant and direct) close to idle, you do not need TCMA or ground mode to expect reduced thrust.
The hamsterwheel ist spinning a lot here, and of course it could be anything including some VHDL FPGA code line or a broken RAM cell in a cheap memory bar within the computer it was compiled with. Anything is possible, but to be honest: development processes, if followed, are usually pushing the probability to a level where it becomes pure theory. BOSCH uses FPGA+\xb5C on the brake control box of cars. They sold 100 millions of those, used 4000h each (car lifetime) without error, with less strict development process. Most errors are made on requirement level, not code.
Also, so far there is no evidence I've seen regarding the 'chicken-egg' problem, did the engines fall below idle (fuel, stall...) and this caused an electrical blackout (-> battery, RAT...) or did an EE problem cause the engines to reduce thrust (FADEC, SW bug...). And where is the common cause in all this?
There has to be a systematic error common to both engines, an external failure affecting both or a dependent fault with one affecting the other within seconds. This is the only thing I think everyone agrees here. And I refuse to beleave the external failure or dependent fault was sitting in the cockpit.
I think it is something not common to every aircraft type for the last 50 years.
So I started searching and found a candidate.
I read myself into the EE architecture of this unique 'bleed-less' design and it's megawatt powergrid since this is the part where I may be able to contribute (and I'm most curious about). Generators on the 787 are >250kW instead of <100kW each and there are two per engine instead of just one. In fact, they can go up to 516 kW and shear off the gearbox at >2200Nm (equal to >2 MW, per generator).
https://www.easa.europa.eu/en/downloads/7641/en (page 11)
So while on any other aircraft the generator is more like the dynamo on your bicycle, those generators are massive (x10).
The gearbox is connected to the HP shaft (N2) on the GEnx. I learned from Wikipedia that RR moved this gearbox to the IP shaft on the Trend 1000. And RR is happy that the A330neo Trend 7000 uses bleed air and less load on the gearbox, since this maintains stability on the HP shaft at light load (also Wikipedia).
Those generators are not in phase and frequency sync, or in other words: If you parallel them, they fight each other, it's like a short. They will almost block if this is not handled by the control box if possible (or some melting fuse blows at some point).
787 electrical system - variable frequency generators?
Somehow I find it hard to believe that they are not able to disturb the engines despite that everyone here so far is claiming that there is no way an electrical problem could influence them because FADEC has it's own supply. I read that one is sufficent to start the engine, usually both are used.
In my mind I find lot's of ways this could influence both engines simultanously. If just the BTBs on the 230V grid got some humidity (hot, no AC, water cooling...) and went up in one big arc (I think they made them semiconductor relays, too).
Could those gearboxes and engines handle 4500Nm / almost 5 MW on each HP shaft, applied within a fraction of a second without any problem?
Or if the engines were in a condition not far from compressor stall, one was stalling and 400kW load jumped from one engines generators to the other...
I did some rough estimation and one of the generators could push N2 below idle in a second or less without fuel just with its normal 250kW load (just inertia).
This is one point which is unique to this airplane model, so maybe worth a closer look.
I know that those engines are burning at >100MW at full power, but how fragile in the balance between compressor load and this one turbine stage on the HP shaft / N2, without the inertia of a 2.8 meter fan? This is just out of my background, any thermodynamic expert here?
Of course I also have no insight in SW and communication within the control boxes, how much they are talking to each other, delaying/ramping load redistribution etc. If FADEC recognizes a flameout, could it instantly command the generators to cut the load, even above idle rpm?
I would assume that some fuel contamination, valve blockade, even compressor stall would pop up slower. But such a generator could kick in within milliseconds.
As a safety guy I learned that one tends to look first at things one is familiar with (SW, HW, mechanics, pilot behaviour, maintainance, depending on one's profession) and in the end it's often the interface and dependent faults within which are not carefully considered (e.g. takeoff situation vs. thermodynamics vs. mechanics vs. power generation vs. humidity vs. generator control...) together with transient behaviour. It was the same with MCAS (safety culture vs. pilot training vs. SW design (repeated action) vs. single AOA input vs. bird strike probability close to ground vs. trim loading/blockade vs. stickshaker noise/distraction).
In fact, I was trying to find information on all those systems and directly found slides on how the engines and generators could be simulated and the power grid tested in a HIL (hardware in the loop) environment. My experience from automotive is that such simulated environments are often far from reality and HIL environment programming finished after the product is already at the customer. But of course its far easier and cheaper to apply and test faults there. But then, some programmer programms what he thinks the reaction of the engine would be.
This 'bleed-less' design was some massive change in airplane EE architecture with hugh consequences on the whole airplane design and extremely hard to fully analyze.
I'm just asking questions and hope that we all learn a lot and this was fully considered or just not an issue. It's just an aspect I found worth mentioning and not only spinning the wheel.
PS: I doubt it was TCMA. The air/ground decision is done in a different box, evaluating 5 inputs in a 1/3 and 1/2 decision according to this discussion. This is then safely sent to the FADEC (as one input) and combined with the thrust lever position and N2. But if the thrust lever position is sensed (redundant and direct) close to idle, you do not need TCMA or ground mode to expect reduced thrust.
4 users liked this post.
2025-06-29T17:02:00
permalink Post: 11913128
From the link above:
The minister called the crash a "rare case". "It has never happened that both engines have shut down together," he said
So they have no clue even with both recorders read out, why both engines shut down at the same time.
Sabotage on the electrical fuels shut down:
Would require detailed knowledge about the wire routing, which is independent for both engine sides, so any "device" would be difficult to get into the electric harness. I would rule that out, unless they find foreign devices wired in on the wreck, because there are way simpler methods to get an airliner down.
Fuel contamination:
There is no smoke, no puff, nothing visible on the exhaust. Both engines went from clean burning to immediate shut down at the same time within less than a second. I think that is close to impossible with any method of fuel contamination you can come up with. There ist always some mixture you would burn and the less perfect burn rate would show as smoke. At take off you have something around 5kg per second fuel burn rate per engine, so you have to come up with non combustible "fuel" in this rate on the exact time on both engines.
Highly improbable.
I find it very disconcerting that with downloaded recorders the investigators seem to have no clue how and why the dual engine shut down happened. How can they be sure that this unrecoverable problem was/is limited to the AI171 flight.
The minister called the crash a "rare case". "It has never happened that both engines have shut down together," he said
So they have no clue even with both recorders read out, why both engines shut down at the same time.
Sabotage on the electrical fuels shut down:
Would require detailed knowledge about the wire routing, which is independent for both engine sides, so any "device" would be difficult to get into the electric harness. I would rule that out, unless they find foreign devices wired in on the wreck, because there are way simpler methods to get an airliner down.
Fuel contamination:
There is no smoke, no puff, nothing visible on the exhaust. Both engines went from clean burning to immediate shut down at the same time within less than a second. I think that is close to impossible with any method of fuel contamination you can come up with. There ist always some mixture you would burn and the less perfect burn rate would show as smoke. At take off you have something around 5kg per second fuel burn rate per engine, so you have to come up with non combustible "fuel" in this rate on the exact time on both engines.
Highly improbable.
I find it very disconcerting that with downloaded recorders the investigators seem to have no clue how and why the dual engine shut down happened. How can they be sure that this unrecoverable problem was/is limited to the AI171 flight.