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| Arrowhead
2025-06-13T09:03:00 permalink Post: 11900213 |
https://assets.publishing.service.go...211_G-POWN.pdf
One example of fuel contamination causing a significant loss of thrust on both engines at low altitude. But it seems extremely unlikely for contaminated fuel to impact both engines at exactly the same time, with no asymmetry and no surges or smoke. What can cause a sudden catastrophic loss of thrust on both engines at exactly the same time? Birds (but no apparent surges) Inadvertent movement of the fuel cut off switches (which would be an incredible error but I suppose it could conceivably be muscle memory having done so recently after the last leg…weirder things have happened. Remember the 767 events of the late 80s) Intentional shutdown of the engines (pilot suicide has happened before) Some catastrophic electrical/FADEC/engine interface failure (which I highly doubt is feasible in a modern 1309 aircraft) I can’t think of any others… I cant think of any reason for electrical failure and "no thrust" (as per statements) without any visual cues other than (a) suicide, or (b) starvation. Is there any electrical failure that can cause fuel valves to close? I dont fly Boeing, so can any Dreamliner driver explain what conditions could trigger an overspeed and auto engine shutdown (quote from Google below)? Would short runway, and hot/low QNH do it? Also, what happened to the order demanding a full power down/recycle every 51 days? The EEC has build in protections to protect the engine. One of these protections is the Engine Overspeed Protection, when the core engine exceeds 120% the EEC shuts off the fuel to the applicable engine. Last edited by Arrowhead; 13th Jun 2025 at 09:46 . |
| Ngineer
2025-06-13T09:11:00 permalink Post: 11900223 |
I didn\x92t think this could be a dual engine failure related accident until reports of RAT deployment started to gather steam.
A few years back a B787 previously had a dual engine shutdown after rollout when the TR was deployed too quickly and not allowing the air/GND logic time to transition to ground mode before the TR deployed. If the TCMA had inadvertently latched the TR deployment from the previous rollout then it theoretically could be possible to shutdown on transition back to air mode. Anything is possible with these high tech machines. 2 users liked this post. |
| flemingcool
2025-06-13T09:26:00 permalink Post: 11900239 |
I didn\x92t think this could be a dual engine failure related accident until reports of RAT deployment started to gather steam.
A few years back a B787 previously had a dual engine shutdown after rollout when the TR was deployed too quickly and not allowing the air/GND logic time to transition to ground mode before the TR deployed. If the TCMA had inadvertently latched the TR deployment from the previous rollout then it theoretically could be possible to shutdown on transition back to air mode. Anything is possible with these high tech machines. RIP to all the victims. |
| lighttwin2
2025-06-13T10:06:00 permalink Post: 11900279 |
This seems to be the best summary so far. Based on the detail of the mayday its probably time to rule out the flaps, load shift, and other suggestions.
I cant think of any reason for "no thrust" (as per ATC) without any visual cues other than (a) suicide, or (b) starvation. Is there any electrical failure that can cause fuel valves to close? I dont fly Boeing, so can any Dreamliner driver explain what conditions could trigger an overspeed and auto engine shutdown (quote from Google below)? Would short runway, and hot/low QNH do it? The EEC has build in protections to protect the engine. One of these protections is the Engine Overspeed Protection, when the core engine exceeds 120% the EEC shuts off the fuel to the applicable engine. Many GE engines - including GEnx-1B/67s - require microprocessors to be routinely replaced due to soldered joints failing after multiple cycles. There is a 2021 AD that notes "This AD was prompted by an in-service occurrence of loss of engine thrust control resulting in uncommanded high thrust" (I cannot post a link but google: 2021-25491 (86 FR 66447)) I am NOT suggesting that this specific failure mode happened here - for one thing, this would happen to one engine, not both. But on any flight it is possible that a unique set of sensor inputs to occur that are the first time any system has encountered them (example: NATS incident in 2023), and then you need failover & redundancy to keep things working. The GE Aviation CCS system, which includes thrust management, has up to now flown for 1m flight hours without incident. It would be interesting to hear the perspectives of any engineers familiar with the system. |
| Compton3fox
2025-06-13T11:45:00 permalink Post: 11900402 |
I didn\x92t think this could be a dual engine failure related accident until reports of RAT deployment started to gather steam.
A few years back a B787 previously had a dual engine shutdown after rollout when the TR was deployed too quickly and not allowing the air/GND logic time to transition to ground mode before the TR deployed. If the TCMA had inadvertently latched the TR deployment from the previous rollout then it theoretically could be possible to shutdown on transition back to air mode. Anything is possible with these high tech machines. been examples in the past where it does something it wasn't supposed to do, causing an incident. |
| violator
2025-06-13T12:56:00 permalink Post: 11900487 |
Question is why both engines lost power . Foreign object ingestion , contaminated fuel or both cutoff levels operated ? We do not know .
Any autothrust discussion is misleading since every pilot in that situation will firewall the levers whatever thrust reduction was selected for TO . the same is true for the RAT discussion- if enough hydraulic pressure was generated or not . The plane pitched up last second so there obviously was control until the end . Of course , without energy pulling alone will not bring you anywhere . Why did both engines fail the same second as they would be cut off ??? Let\x92s be careful about absolutes. Emirates 521 and Turkish 1951 are both examples of crews not firewalling the thrust levers despite low energy. The late pitch up could be due to the onset of a stall not an order from the crew. TCMA is function which can reduce thrust on both engines simultaneously. It had done so in error in the past resulting in an AD. It uses air/ground logic so that it only operates on the ground, however note that at the point of thrust loss the gear is still down without any movement of the gear or doors. I would expect gear retraction to start before that height. Could we imagine an air/ground logic fault inhibiting gear retraction and allowing TCMA, which triggered (for whatever reason!) causing dual thrust loss? I would expect this to be in the realms of a combination of failures shown to be extremely impossible, but\x85 2 users liked this post. |
| Luc Lion
2025-06-13T14:05:00 permalink Post: 11900549 |
I didn\x92t think this could be a dual engine failure related accident until reports of RAT deployment started to gather steam.
A few years back a B787 previously had a dual engine shutdown after rollout when the TR was deployed too quickly and not allowing the air/GND logic time to transition to ground mode before the TR deployed. If the TCMA had inadvertently latched the TR deployment from the previous rollout then it theoretically could be possible to shutdown on transition back to air mode. Anything is possible with these high tech machines. ANA 787 Engines shutdown during landing and in AvHerald: https://avherald.com/h?article=4c2fe53a&opt=0 Just to clarify one point: the ANA B787 was powered with RR Trent 1000 engines while the Air India had GEnx-1B67 engines. So, the Air India thrust failure may still have its source in the TCMA system, however, if it's the case, the logical path must be somewhat different than for the thrust reversers of the ANA airplane. |
| lighttwin2
2025-06-13T14:32:00 permalink Post: 11900574 |
This was handled in this PPrune thread:
Just to clarify one point: the ANA B787 was powered with RR Trent 1000 engines while the Air India had GEnx-1B67 engines. So, the Air India thrust failure may still have its source in the TCMA system, however, if it's the case, the logical path must be somewhat different than for the thrust reversers of the ANA airplane. Note, the EEC module in GEnx itself is subject to periodic replacement under an AD due to risk of solder failure, but this seems unlikely to be related as would only impact a single engine. |
| JustusW
2025-06-13T16:31:00 permalink Post: 11900677 |
Correct, but if they retract flaps while the engines are producing takeoff thrust and they are somehow losing altitude they definitely should speed up.
There are strong reasons to doubt the flaps had anything to do with the accident, I agree with the following sentiment completely: I was taught (only as familiarization for my job as ATC) that during takeoff the pilot flying should have their hand on the throttle levers. Is that generally correct? If yes, will changes to throttle settings always be reflected in the actual physical position of the throttle levers or are there situations where the actual commanded throttle could differ from the physical lever position? The interaction with the TCMA in particular is of interest to me. Regards, Justus 1 user liked this post. |
| Wazzajnr
2025-06-13T18:00:00 permalink Post: 11900751 |
Let\x92s be careful about absolutes. Emirates 521 and Turkish 1951 are both examples of crews not firewalling the thrust levers despite low energy. The late pitch up could be due to the onset of a stall not an order from the crew.
TCMA is function which can reduce thrust on both engines simultaneously. It had done so in error in the past resulting in an AD. It uses air/ground logic so that it only operates on the ground, however note that at the point of thrust loss the gear is still down without any movement of the gear or doors. I would expect gear retraction to start before that height. Could we imagine an air/ground logic fault inhibiting gear retraction and allowing TCMA, which triggered (for whatever reason!) causing dual thrust loss? I would expect this to be in the realms of a combination of failures shown to be extremely impossible, but\x85 6 users liked this post. |
| tdracer
2025-06-13T18:41:00 permalink Post: 11900793 |
OK, another hour spent going through all the posts since I was on last night...
I won't quote the relevant posts as they go back ~15 pages, but a few more comments: TAT errors affecting N1 power set: The FADEC logic (BTW, this is pretty much common on all Boeing FADEC) will use aircraft TAT if it agrees with the dedicated engine inlet temp probe - but if they differ it will use the engine probe . The GE inlet temp probe is relatively simple and unheated, so (unlike a heated probe) a blocked or contaminated probe will still read accurately - just with greater 'lag' to actual temperature changes. TCMA - first off, I have to admit that this does look rather like an improper TCMA activation, but that is very, very unlikely. For those who don't know, TCMA is a system to shutdown a runaway engine that's not responding to the thrust lever - basic logic is an engine at high power with the thrust lever at/near idle, and the engine not decelerating. However, TCMA is only active on the ground (unfamiliar with the 787/GEnx TCMA air/ground logic - on the 747-8 we used 5 sources of air/ground - three Radio Altimeters and two Weight on Wheels - at least one of each had to indicate ground to enable TCMA). TCMA will shutdown the engine via the N2 overspeed protection - nearly instantaneous. For this to be TCMA, it would require at least two major failures - improper air ground indication or logic, and improper TCMA activation logic (completely separate software paths in the FADEC). Like I said, very, very unlikely. Fuel contamination/filter blockage: The fuel filters have a bypass - if the delta P across the filter becomes excessive, the filter bypasses and provides the contaminated fuel to the engine. Now this contaminated fuel could easy foul up the fuel metering unit causing a flameout, but to happen to two engines at virtually the same time would be tremendous unlikely. Auto Thrust thrust lever retard - the TO lockup in the logic makes this very unlikely (it won't unlock below (IIRC) 400 ft., and even that requires a separate pilot action such as a mode select change or thrust lever movement). And if it did somehow happen, all the pilot needs to do is push the levers back up. Engine parameters on the FDR: I don't know what exactly is on the 787 FDR with regards to engine parameters, but rest assured that there is plenty of engine data that gets recorded - most at one/second. Getting the FDR readout from a modern FDR is almost an embarrassment of riches. Assuming the data is intact, we'll soon have a very good idea of what the engines were doing 17 users liked this post. |
| violator
2025-06-13T18:58:00 permalink Post: 11900812 |
OK, another hour spent going through all the posts since I was on last night...
I won't quote the relevant posts as they go back ~15 pages, but a few more comments: TAT errors affecting N1 power set: The FADEC logic (BTW, this is pretty much common on all Boeing FADEC) will use aircraft TAT if it agrees with the dedicated engine inlet temp probe - but if they differ it will use the engine probe . The GE inlet temp probe is relatively simple and unheated, so (unlike a heated probe) a blocked or contaminated probe will still read accurately - just with greater 'lag' to actual temperature changes. TCMA - first off, I have to admit that this does look rather like an improper TCMA activation, but that is very, very unlikely. For those who don't know, TCMA is a system to shutdown a runaway engine that's not responding to the thrust lever - basic logic is an engine at high power with the thrust lever at/near idle, and the engine not decelerating. However, TCMA is only active on the ground (unfamiliar with the 787/GEnx TCMA air/ground logic - on the 747-8 we used 5 sources of air/ground - three Radio Altimeters and two Weight on Wheels - at least one of each had to indicate ground to enable TCMA). TCMA will shutdown the engine via the N2 overspeed protection - nearly instantaneous. For this to be TCMA, it would require at least two major failures - improper air ground indication or logic, and improper TCMA activation logic (completely separate software paths in the FADEC). Like I said, very, very unlikely. Fuel contamination/filter blockage: The fuel filters have a bypass - if the delta P across the filter becomes excessive, the filter bypasses and provides the contaminated fuel to the engine. Now this contaminated fuel could easy foul up the fuel metering unit causing a flameout, but to happen to two engines at virtually the same time would be tremendous unlikely. Auto Thrust thrust lever retard - the TO lockup in the logic makes this very unlikely (it won't unlock below (IIRC) 400 ft., and even that requires a separate pilot action such as a mode select change or thrust lever movement). And if it did somehow happen, all the pilot needs to do is push the levers back up. Engine parameters on the FDR: I don't know what exactly is on the 787 FDR with regards to engine parameters, but rest assured that there is plenty of engine data that gets recorded - most at one/second. Getting the FDR readout from a modern FDR is almost an embarrassment of riches. Assuming the data is intact, we'll soon have a very good idea of what the engines were doing |
| Turkey Brain
2025-06-13T21:57:00 permalink Post: 11900954 |
At this stage, at least two scenarios seem highly plausible:
1. Technical issue Airliners rely on air/ground logic , which is fundamental to how systems operate. There have been numerous crashes and serious incidents linked to this logic functioning incorrectly. Some engineering tests require the air/ground switch to be set in a particular mode. If it's inadvertently left in engineering mode—or if the system misinterprets the mode—this can cause significant problems.
2. Pilot misselection of fuel control switches to cutoff This is still a very real possibility. If it occurred, the pilot responsible may not have done it consciously—his mindset could have been in a different mode. There’s precedent: an A320 pilot once inadvertently shut down both engines over Paris. Fortunately, the crew managed to restart them. Afterward, the pilot reportedly couldn’t explain his actions. If something similar happened here, then when the pilots realized the engines had stopped producing thrust, pushing the levers forward would have had no effect. It’s easy to overlook that the fuel switches are in the wrong position—they're far from the normal scan pattern. And with the ground rushing up, the view outside would’ve been far more commanding. Speaking personally, when I shut down engines at the end of a flight, I consciously force myself to operate each fuel switch independently and with full attention. I avoid building muscle memory that might lead to switching off both engines in a fast, well-practiced habit. If this is a technical issue, I assume we’ll know soon enough. 3 users liked this post. |
| lighttwin2
2025-06-13T22:05:00 permalink Post: 11900958 |
TCMA - first off, I have to admit that this does look rather like an improper TCMA activation, but that is very, very unlikely. For those who don't know, TCMA is a system to shutdown a runaway engine that's not responding to the thrust lever - basic logic is an engine at high power with the thrust lever at/near idle, and the engine not decelerating. However, TCMA is only active on the ground (unfamiliar with the 787/GEnx TCMA air/ground logic - on the 747-8 we used 5 sources of air/ground - three Radio Altimeters and two Weight on Wheels - at least one of each had to indicate ground to enable TCMA). TCMA will shutdown the engine via the N2 overspeed protection - nearly instantaneous. For this to be TCMA, it would require at least two major failures - improper air ground indication or logic, and improper TCMA activation logic (completely separate software paths in the FADEC). Like I said, very, very unlikely. Two thoughts re TCMA: 1) Is it possible a false TCMA activation could have occurred just before, or concurrently with, the a/c leaving the ground, with the resulting loss of thrust and electrical power not being apparent for another (say) 10s); 2) As you say two simultaneous failures very unlikely... except that it did happen to that ANA flight, albeit during ground state. |
| fdr
2025-06-13T22:13:00 permalink Post: 11900962 |
At this stage, at least two scenarios seem highly plausible:
1. Technical issue Airliners rely on air/ground logic , which is fundamental to how systems operate. There have been numerous crashes and serious incidents linked to this logic functioning incorrectly. Some engineering tests require the air/ground switch to be set in a particular mode. If it's inadvertently left in engineering mode—or if the system misinterprets the mode—this can cause significant problems.
2. Pilot misselection of fuel control switches to cutoff This is still a very real possibility. If it occurred, the pilot responsible may not have done it consciously—his mindset could have been in a different mode. There’s precedent: an A320 pilot once inadvertently shut down both engines over Paris. Fortunately, the crew managed to restart them. Afterward, the pilot reportedly couldn’t explain his actions. If something similar happened here, then when the pilots realized the engines had stopped producing thrust, pushing the levers forward would have had no effect. It’s easy to overlook that the fuel switches are in the wrong position—they're far from the normal scan pattern. And with the ground rushing up, the view outside would’ve been far more commanding. Speaking personally, when I shut down engines at the end of a flight, I consciously force myself to operate each fuel switch independently and with full attention. I avoid building muscle memory that might lead to switching off both engines in a fast, well-practiced habit. If this is a technical issue, I assume we’ll know soon enough. On item 2, the video shows no asymmetry at any time, so there is only a symmetric failure of the engines possible. Back on a B747 classic, you could chop all 4 engines at the same time with one hand, on a B737, also, not so much on a B777 or B787. I would doubt that anyone used two hands to cut the fuel at screen height. Note, there was a B744 that lost one engine in cruise when a clip board fell off the coaming. Didn't happen twice, and it only happened to one engine.
Yes indeed, the moment they pulled the gear lever, as we see the gear begin the retraction process, and then suddenly stop. Almost as if they suddenly lost power.
We can see the landing gear retraction process begin. We see the bogies tilted in the second video. We can hear the RAT. We can see the RAT. We can see the flaps extended in the video and at the crash site. There isn't actually a single piece of evidence the flaps were raised, it's just a conclusion people jumped too before evidence began to emerge. The crazy thing is, when the report comes out and there is no mention of flaps none of the people who have been pushing the flap theory will self reflect or learn anything. They'll think those of us who didn't buy into it were just lucky, rather than it being down to use of fairly simple critical thinking. Neila83 is correct, the gear tilt pre retraction is rear wheels low, and at the commencement of the selection of the retraction cycle (generally), There is enough in the way of anomalies here to end up with regulatory action, and airlines themselves should/will be starting to pore over their systems and decide if they are comfortable with the airworthiness of the aircraft at this moment. A latent single point of failure is not a comfortable place to be. Inhibiting TCMA might be a good interim option, that system could have been negated by having the ATR ARM switches....(Both)... ARM deferred to the before takeoff checks. The EAFR recovery should result in action within the next 24-48 hours. Boeing needs to be getting their tiger teams warmed up, they can ill afford to have a latent system fault discovered that is not immediately responded to, and the general corporate response of "blame the pilots" is not likely to win any future orders. I think we are about to have some really busy days for the OEM. Not sure that Neila83 is that far off the mark at all. Last edited by fdr; 14th Jun 2025 at 01:21 . Reason: corrected for B788 by Capt Bloggs! 8 users liked this post. |
| tdracer
2025-06-13T22:41:00 permalink Post: 11900973 |
Since TCMA keeps getting discussed, let me add a bit more of what I know:
There were two on-ground events - as noted one each Rolls and GE. My understanding is that both events involved rapid thrust lever movements into/out-of reverse selection (i.e. reverse - forward - reverse in rapid succession). This rapid thrust lever movement - combined with the engine trying it's best to react to those movements - tricked the TCMA logic into thinking the engine was accelerating uncontrollably. There are two key points here - on-ground, and rapid thrust lever movements. There is absolutely no reason why the thrust levers should be moving at all during this event, and it doesn't appear to have occurred while the aircraft was still on the ground. I was in this business long enough to know that you 'never say never', it would take a pretty gross error in the TCMA logic for it to have activated without a large thrust lever movement. 9 users liked this post. |
| oldmacdonald757
2025-06-13T23:18:00 permalink Post: 11900990 |
Cannot post screen grab of MMEL unfortunately.
TCMA is receiving quite a lot of attention on a number of forums. Looking through MMEL/MEL, it might appear that TCMA is only fitted to aircraft powered by RR-1000 turbofans. The accident aircraft (R.I.P.) was powered by General Electric turbofans. The MMEL/MEL makes no mention of TCMA although there may be a system of similar functions with different nomenclature. (see 787 MMEL ATA 73-21-06 \x84TCMA\x94) |
| tdracer
2025-06-14T00:30:00 permalink Post: 11901028 |
Cannot post screen grab of MMEL unfortunately.
TCMA is receiving quite a lot of attention on a number of forums. Looking through MMEL/MEL, it might appear that TCMA is only fitted to aircraft powered by RR-1000 turbofans. The accident aircraft (R.I.P.) was powered by General Electric turbofans. The MMEL/MEL makes no mention of TCMA although there may be a system of similar functions with different nomenclature. (see 787 MMEL ATA 73-21-06 \x84TCMA\x94) 4 users liked this post. |
| jetpig32
2025-06-14T03:38:00 permalink Post: 11901111 |
Only two 787 dual loss of thrust situations I can think of is Jetstar into Osaka (biocide issues) and Jal on rollout with a TCMA malfunction.
1 user liked this post. |
| eagle21
2025-06-14T07:20:00 permalink Post: 11901189 |
The TCMA activated on the ANA, rolling back both engines on landing. This is the only time a double engine issue has been reported on a 787z
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