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…
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 .
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.
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.
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
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.
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
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
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.
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)
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.
2025-06-14T13:40:00
permalink Post: 11901495
Fuel cutoff switches
My next question, again I believe not discussed, is what do the 787 Fuel Cutoff switches actually do? Obviously, they cut off the fuel supplies to the engines - pretty important in engine fire and other scenarios, but goes without saying. The real question is, what do they activate (or deactivate)? I'm assuming a simple solenoid valve, which is open when powered and closed when unpowered, but of course, there will (certainly) be Electro-Mechanical or Solid-State (Electronic) relays between the switches and the (solenoid valves).
I guess the next obvious question is, is there anything else that can turn off those Fuel Cutoff Valves - a computer condition for example. I'm assuming not, but I think it needs to be considered.
Taking each switch individually, next, since this is part of an electrical circuit, and of necessity must include Electrical Relays, there is certainly at least one and in all probability two electric Power Sources involved in this circuit. One supply which passes through the switch to activate the relay, and, I'm assuming, a second, higher current and probably higher voltage supply which drives the (solenoid?) valve.
As I see it, interrupting either supply will have the same effect - if the system is wired in the Positive-Postive sense, meaning a current through the switch causes the relay to pass a current through the (solenoid). If either of these supplies is cut, the Fuel Shutoffs will shut off the fuel. So, the question is, where do these supplies come from, and under what circumstances could they be cut off?
Sure, it looks to some (myself included) like a near simultaneous cutoff of both engines, but that doesn't have to have been caused by either of the pilots. I know there is huge redundancy built into the 787 Electrical Systems, but some of the evidence is suggesting that there was something not right with the plane's electrical system. I'm also fairly sure that there will be parts and places where certain faults can take the system down, despite the redundancy. I can't say where, but it's very difficult to design a perfect system, especially where there has to be transfers between multiple potential supplies and single actuators, motors or valves.
Having spent years repairing electrical and electronic systems, I know that the most difficult of all electrical faults are the intermittent ones. And I suspect that this is at the root of this crash. An intermittent or faulty AOA sensor has "caused" (provoked) multiple famous crashes... Can't find the one I'm looking for (pre-1980, I think) as the Max AOA issues dominate.
I can cite a very personal example, which involved the electrical supply to my house. I had several computers running 24x365 so of course, ran them off a UPS, which turned out to be a very good thing. I started to notice that at certain times, the UPS would activate - it would cut in and take over the computer loads, its alarm would go off to indicate a power fault. But the power was still on! This carried on for weeks and I initially blamed the UPS. Then, I noticed that it only happened on very hot afternoons... Long story short, the fault was caused by an electrical linesman, probably 30 years earlier, failing to tighten up a joint clamp on the phase wire to our house, across the street. Heating caused expansion then movement, and the power would momentarily go off then back on, and the UPS detected this. I note that this crash was on a hot day, and maybe this plane (which I believe was repositioned for the flight), had not been operating in such high temperatures recently, meaning the problem went unnoticed.
I guess the next obvious question is, is there anything else that can turn off those Fuel Cutoff Valves - a computer condition for example. I'm assuming not, but I think it needs to be considered.
Taking each switch individually, next, since this is part of an electrical circuit, and of necessity must include Electrical Relays, there is certainly at least one and in all probability two electric Power Sources involved in this circuit. One supply which passes through the switch to activate the relay, and, I'm assuming, a second, higher current and probably higher voltage supply which drives the (solenoid?) valve.
As I see it, interrupting either supply will have the same effect - if the system is wired in the Positive-Postive sense, meaning a current through the switch causes the relay to pass a current through the (solenoid). If either of these supplies is cut, the Fuel Shutoffs will shut off the fuel. So, the question is, where do these supplies come from, and under what circumstances could they be cut off?
Sure, it looks to some (myself included) like a near simultaneous cutoff of both engines, but that doesn't have to have been caused by either of the pilots. I know there is huge redundancy built into the 787 Electrical Systems, but some of the evidence is suggesting that there was something not right with the plane's electrical system. I'm also fairly sure that there will be parts and places where certain faults can take the system down, despite the redundancy. I can't say where, but it's very difficult to design a perfect system, especially where there has to be transfers between multiple potential supplies and single actuators, motors or valves.
Having spent years repairing electrical and electronic systems, I know that the most difficult of all electrical faults are the intermittent ones. And I suspect that this is at the root of this crash. An intermittent or faulty AOA sensor has "caused" (provoked) multiple famous crashes... Can't find the one I'm looking for (pre-1980, I think) as the Max AOA issues dominate.
I can cite a very personal example, which involved the electrical supply to my house. I had several computers running 24x365 so of course, ran them off a UPS, which turned out to be a very good thing. I started to notice that at certain times, the UPS would activate - it would cut in and take over the computer loads, its alarm would go off to indicate a power fault. But the power was still on! This carried on for weeks and I initially blamed the UPS. Then, I noticed that it only happened on very hot afternoons... Long story short, the fault was caused by an electrical linesman, probably 30 years earlier, failing to tighten up a joint clamp on the phase wire to our house, across the street. Heating caused expansion then movement, and the power would momentarily go off then back on, and the UPS detected this. I note that this crash was on a hot day, and maybe this plane (which I believe was repositioned for the flight), had not been operating in such high temperatures recently, meaning the problem went unnoticed.
2 users liked this post.
2025-06-14T13:43:00
permalink Post: 11901499
Reports coming in that Indian regulator has sent out a note for inspection of all GenX engines on the 787
2025-06-14T20:48:00
permalink Post: 11901821
Another hour spent sifting through the stuff since last night (my sympathies to the mods
). A few more comments:
"Real time engine monitoring" is typically not 'real time' - it's recorded and sent in periodic bursts. Very unlikely anything was sent from the event aircraft on this flight.
Commanded engine cutoff - the aisle stand fuel switch sends electrical signals to the spar valve and the "High Pressure Shutoff Valve" (HPSOV) in the Fuel Metering Unit, commanding them to open/close using aircraft power. The HPSOV is solenoid controlled, and near instantaneous. The solenoid is of a 'locking' type that needs to be powered both ways (for obvious reasons, you wouldn't want a loss of electrical power to shut down the engine). The fire handle does the same thing, via different electrical paths (i.e. separate wiring).
As I've noted previously, a complete loss of aircraft electrical power would not cause the engines to flameout (or even lose meaningful thrust) during takeoff. In the takeoff altitude envelope, 'suction feed' (I think Airbus calls it 'gravity feed') is more than sufficient to supply the engine driven fuel pumps. It's only when you get up to ~20k ft. that suction feed can become an issue - and this event happened near sea level.
Not matter what's happening on the aircraft side - pushing the thrust levers to the forward stop will give you (at least) rated takeoff power since the only thing required from the aircraft is fuel and thrust lever position (and the thrust lever position resolver is powered by the FADEC).
The TCMA logic is designed and scrubbed so as to be quite robust - flight test data of the engine response to throttle slams is reviewed to insure there is adequate margin between the TCMA limits and the actual engine responses to prevent improper TCMA activation. Again, never say never, but a whole lot would have had to go wrong in the TCMA logic for it to have activated on this flight.
Now, if I assume the speculation that the RAT deployed is correct, I keep coming up with two potential scenarios that could explain what's known regarding this accident:
1) TCMA activation shutdown the engines
or
2) The fuel cutoff switches were activated.
I literally can come up with no other plausible scenarios.
In all due respect to all the pilots on this forum, I really hope it wasn't TCMA. It wouldn't be the first time a mandated 'safety system' has caused an accident (it wouldn't just be Boeing and GE - TCMA was forced by the FAA and EASA to prevent a scenario that had never caused a fatal accident) - and there would be a lot embarrassing questions for all involved. But I personally know many of the people who created, validated, and certified the GEnx-1B TCMA logic - and can't imagine what they would be going through if they missed something (coincidentally, one of them was at my birthday party last weekend and inevitably we ended up talking about what we used to do at Boeing (he's also retired)). Worse, similar TCMA logic is on the GEnx-2B (747-8) - which I was personally responsible for certifying - as well as the GE90-115B and the 737 MAX Leap engine - the consequences of that logic causing this accident would be massive.
). A few more comments:
"Real time engine monitoring" is typically not 'real time' - it's recorded and sent in periodic bursts. Very unlikely anything was sent from the event aircraft on this flight.
Commanded engine cutoff - the aisle stand fuel switch sends electrical signals to the spar valve and the "High Pressure Shutoff Valve" (HPSOV) in the Fuel Metering Unit, commanding them to open/close using aircraft power. The HPSOV is solenoid controlled, and near instantaneous. The solenoid is of a 'locking' type that needs to be powered both ways (for obvious reasons, you wouldn't want a loss of electrical power to shut down the engine). The fire handle does the same thing, via different electrical paths (i.e. separate wiring).
As I've noted previously, a complete loss of aircraft electrical power would not cause the engines to flameout (or even lose meaningful thrust) during takeoff. In the takeoff altitude envelope, 'suction feed' (I think Airbus calls it 'gravity feed') is more than sufficient to supply the engine driven fuel pumps. It's only when you get up to ~20k ft. that suction feed can become an issue - and this event happened near sea level.
Not matter what's happening on the aircraft side - pushing the thrust levers to the forward stop will give you (at least) rated takeoff power since the only thing required from the aircraft is fuel and thrust lever position (and the thrust lever position resolver is powered by the FADEC).
The TCMA logic is designed and scrubbed so as to be quite robust - flight test data of the engine response to throttle slams is reviewed to insure there is adequate margin between the TCMA limits and the actual engine responses to prevent improper TCMA activation. Again, never say never, but a whole lot would have had to go wrong in the TCMA logic for it to have activated on this flight.
Now, if I assume the speculation that the RAT deployed is correct, I keep coming up with two potential scenarios that could explain what's known regarding this accident:
1) TCMA activation shutdown the engines
or
2) The fuel cutoff switches were activated.
I literally can come up with no other plausible scenarios.
In all due respect to all the pilots on this forum, I really hope it wasn't TCMA. It wouldn't be the first time a mandated 'safety system' has caused an accident (it wouldn't just be Boeing and GE - TCMA was forced by the FAA and EASA to prevent a scenario that had never caused a fatal accident) - and there would be a lot embarrassing questions for all involved. But I personally know many of the people who created, validated, and certified the GEnx-1B TCMA logic - and can't imagine what they would be going through if they missed something (coincidentally, one of them was at my birthday party last weekend and inevitably we ended up talking about what we used to do at Boeing (he's also retired)). Worse, similar TCMA logic is on the GEnx-2B (747-8) - which I was personally responsible for certifying - as well as the GE90-115B and the 737 MAX Leap engine - the consequences of that logic causing this accident would be massive.
67 users liked this post.
2025-06-14T21:27:00
permalink Post: 11901855
Another hour spent sifting through the stuff since last night (my sympathies to the mods
). A few more comments:
"Real time engine monitoring" is typically not 'real time' - it's recorded and sent in periodic bursts. Very unlikely anything was sent from the event aircraft on this flight.
Commanded engine cutoff - the aisle stand fuel switch sends electrical signals to the spar valve and the "High Pressure Shutoff Valve" (HPSOV) in the Fuel Metering Unit, commanding them to open/close using aircraft power. The HPSOV is solenoid controlled, and near instantaneous. The solenoid is of a 'locking' type that needs to be powered both ways (for obvious reasons, you wouldn't want a loss of electrical power to shut down the engine). The fire handle does the same thing, via different electrical paths (i.e. separate wiring).
As I've noted previously, a complete loss of aircraft electrical power would not cause the engines to flameout (or even lose meaningful thrust) during takeoff. In the takeoff altitude envelope, 'suction feed' (I think Airbus calls it 'gravity feed') is more than sufficient to supply the engine driven fuel pumps. It's only when you get up to ~20k ft. that suction feed can become an issue - and this event happened near sea level.
Not matter what's happening on the aircraft side - pushing the thrust levers to the forward stop will give you (at least) rated takeoff power since the only thing required from the aircraft is fuel and thrust lever position (and the thrust lever position resolver is powered by the FADEC).
The TCMA logic is designed and scrubbed so as to be quite robust - flight test data of the engine response to throttle slams is reviewed to insure there is adequate margin between the TCMA limits and the actual engine responses to prevent improper TCMA activation. Again, never say never, but a whole lot would have had to go wrong in the TCMA logic for it to have activated on this flight.
Now, if I assume the speculation that the RAT deployed is correct, I keep coming up with two potential scenarios that could explain what's known regarding this accident:
1) TCMA activation shutdown the engines
or
2) The fuel cutoff switches were activated.
I literally can come up with no other plausible scenarios.
In all due respect to all the pilots on this forum, I really hope it wasn't TCMA. It wouldn't be the first time a mandated 'safety system' has caused an accident (it wouldn't just be Boeing and GE - TCMA was forced by the FAA and EASA to prevent a scenario that had never caused a fatal accident) - and there would be a lot embarrassing questions for all involved. But I personally know many of the people who created, validated, and certified the GEnx-1B TCMA logic - and can't imagine what they would be going through if they missed something (coincidentally, one of them was at my birthday party last weekend and inevitably we ended up talking about what we used to do at Boeing (he's also retired)). Worse, similar TCMA logic is on the GEnx-2B (747-8) - which I was personally responsible for certifying - as well as the GE90-115B and the 737 MAX Leap engine - the consequences of that logic causing this accident would be massive.
). A few more comments:
"Real time engine monitoring" is typically not 'real time' - it's recorded and sent in periodic bursts. Very unlikely anything was sent from the event aircraft on this flight.
Commanded engine cutoff - the aisle stand fuel switch sends electrical signals to the spar valve and the "High Pressure Shutoff Valve" (HPSOV) in the Fuel Metering Unit, commanding them to open/close using aircraft power. The HPSOV is solenoid controlled, and near instantaneous. The solenoid is of a 'locking' type that needs to be powered both ways (for obvious reasons, you wouldn't want a loss of electrical power to shut down the engine). The fire handle does the same thing, via different electrical paths (i.e. separate wiring).
As I've noted previously, a complete loss of aircraft electrical power would not cause the engines to flameout (or even lose meaningful thrust) during takeoff. In the takeoff altitude envelope, 'suction feed' (I think Airbus calls it 'gravity feed') is more than sufficient to supply the engine driven fuel pumps. It's only when you get up to ~20k ft. that suction feed can become an issue - and this event happened near sea level.
Not matter what's happening on the aircraft side - pushing the thrust levers to the forward stop will give you (at least) rated takeoff power since the only thing required from the aircraft is fuel and thrust lever position (and the thrust lever position resolver is powered by the FADEC).
The TCMA logic is designed and scrubbed so as to be quite robust - flight test data of the engine response to throttle slams is reviewed to insure there is adequate margin between the TCMA limits and the actual engine responses to prevent improper TCMA activation. Again, never say never, but a whole lot would have had to go wrong in the TCMA logic for it to have activated on this flight.
Now, if I assume the speculation that the RAT deployed is correct, I keep coming up with two potential scenarios that could explain what's known regarding this accident:
1) TCMA activation shutdown the engines
or
2) The fuel cutoff switches were activated.
I literally can come up with no other plausible scenarios.
In all due respect to all the pilots on this forum, I really hope it wasn't TCMA. It wouldn't be the first time a mandated 'safety system' has caused an accident (it wouldn't just be Boeing and GE - TCMA was forced by the FAA and EASA to prevent a scenario that had never caused a fatal accident) - and there would be a lot embarrassing questions for all involved. But I personally know many of the people who created, validated, and certified the GEnx-1B TCMA logic - and can't imagine what they would be going through if they missed something (coincidentally, one of them was at my birthday party last weekend and inevitably we ended up talking about what we used to do at Boeing (he's also retired)). Worse, similar TCMA logic is on the GEnx-2B (747-8) - which I was personally responsible for certifying - as well as the GE90-115B and the 737 MAX Leap engine - the consequences of that logic causing this accident would be massive.
5 users liked this post.
2025-06-14T21:39:00
permalink Post: 11901865
TCMA
Which side of V1 does TCMA lurk? If a pilot closes the throttles to abort, does the system allow it? After all, "too low thrust" is outside the contour....
Ya know, when every conceivable possibility (or close) has been de wormed, it"s usually something impossible, or too fearful...(Or dishonest, fraudulent, criminal ....etc ,?
Which side of V1 does TCMA lurk? If a pilot closes the throttles to abort, does the system allow it? After all, "too low thrust" is outside the contour....
Ya know, when every conceivable possibility (or close) has been de wormed, it"s usually something impossible, or too fearful...(Or dishonest, fraudulent, criminal ....etc ,?
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.
2 users liked this post.
2025-06-14T21:59:00
permalink Post: 11901875
From tdracer
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.
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.
2025-06-14T22:13:00
permalink Post: 11901888
From tdracer
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.
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.
1 user liked this post.
2025-06-14T23:20:00
permalink Post: 11901949
... The TCMA logic is designed and scrubbed so as to be quite robust - flight test data of the engine response to throttle slams is reviewed to insure there is adequate margin between the TCMA limits and the actual engine responses to prevent improper TCMA activation. Again, never say never, but a whole lot would have had to go wrong in the TCMA logic for it to have activated on this flight.
Now, if I assume the speculation that the RAT deployed is correct, I keep coming up with two potential scenarios that could explain what's known regarding this accident:
1) TCMA activation shutdown the engines
or
2) The fuel cutoff switches were activated.
I literally can come up with no other plausible scenarios.
In all due respect to all the pilots on this forum, I really hope it wasn't TCMA. It wouldn't be the first time a mandated 'safety system' has caused an accident (it wouldn't just be Boeing and GE - TCMA was forced by the FAA and EASA to prevent a scenario that had never caused a fatal accident) ...
5 users liked this post.
2025-06-14T23:54:00
permalink Post: 11901974
From tdracer
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.
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.
Of course you can have two or three systems that are coded by different teams, using different languages, running in different hardware, even if they are fed from the same sensors, as long as you have many sensors (as tdracer has indicated, 5 inputs on the 747 for instance - although only needing 2 to be true does seem to reduce that margin for error somewhat).
If these two or three systems all have to send independent signals to the downstream hardware (the engine in this case) and the engine requires more than one signal to take the dangerous action like shutdown, then you're more protected, but that doesn't seem to be how the 787 works from the descriptions here by the experts like td and fdr. But please correct me if I'm wrong on that.
Its hard to imagine how else you could simultaneously cut both engines any other way, as tdracer said, other than human action or by software command. And software command means software failure. So information and discussion about exactly how redundant the software that takes this decision is would seem a good direction to move this discussion in. Is it truly only redundant 'internally' to itself, the module that sends this message to the engines? We heard about the 32 bit overflow bug that can shutdown engines - is it really that hard to believe that it has no other similar bugs when that one slipped through the testing?
2025-06-15T01:43:00
permalink Post: 11902040
MELs?
From tdracer
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.
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.
2025-06-15T04:19:00
permalink Post: 11902094
Okay! Many thanks for that! Of course, it very much complicates the picture, and I'm very puzzled as to how the Fuel Cutoff Switches and Valves operate. Apparently, the TCAM system shuts off an errant engine on the ground at least, but my concern is not with the software but the hardware. It obviously has an Output going into the Fuel Shutoff system. If the TCAM unit loses power, can that output cause the Cutoff process (powered by the engine-dedicated generator) to be activated? I guess that's the $64 billion question, but if MCAS is any example, then: Probably!
TCMA (not TCAM) - Thrust Control Malfunction Accommodation - is a FADEC based system. It's resident in the engine FADEC (aka EEC) - the ONLY inputs from the aircraft that go into the TCMA is air/ground (to enable) and thrust lever position (to determine if the engine is doing what it's being commanded to do. The FADEC has the ability to shutdown the engine via the N2 overspeed protection system - this is separate from the aircraft run/cutoff signal, although it uses the same HPSOV to effect the shutdown. That same system is used by TCMA to shutoff fuel if it determines the engine is 'running away'.
Hint, you might try going back a few pages and reading where all this has been posted previously.
33 users liked this post.
2025-06-15T05:45:00
permalink Post: 11902127
TCMA (not TCAM) - Thrust Control Malfunction Accommodation - is a FADEC based system. It's resident in the engine FADEC (aka EEC) - the ONLY inputs from the aircraft that go into the TCMA is air/ground (to enable) and thrust lever position (to determine if the engine is doing what it's being commanded to do. The FADEC has the ability to shutdown the engine via the N2 overspeed protection system - this is separate from the aircraft run/cutoff signal, although it uses the same HPSOV to effect the shutdown. That same system is used by TCMA to shutoff fuel if it determines the engine is 'running away'.
In software development, we always have the deadlock risk when we disable a function during a system mode shift. In case an erroneous decision was made just prior to this mode shift, it cant be correctedt as the function itself got disabled after mode shift. Normally we have a monitoring function alway active to correct this.
2025-06-15T06:47:00
permalink Post: 11902155
I hate to disappoint you, but the people (like me) who design, test, and certify aircraft are not idiots. We design for failures. Yes, on rare occasion, something gets missed (e.g. MCAS), but we know that aircraft power systems sometimes fail (or suffer short term interuptions) and we design for that. EVERY VALVE IN THE FUEL SYSTEM MUST BE POWERED TO CHANGE STATE!!!! If electrical power is lost, they just stay where they are. The engine fuel valve must be powered open, and it must be powered closed. Same with the spar valve. The pilot moves a switch, that provides electrical signals to the spar valve and the engine fuel valve to open or close. It's
not
complicated and has been in use for decades.
TCMA (not TCAM) - Thrust Control Malfunction Accommodation - is a FADEC based system. It's resident in the engine FADEC (aka EEC) - the ONLY inputs from the aircraft that go into the TCMA is air/ground (to enable) and thrust lever position (to determine if the engine is doing what it's being commanded to do. The FADEC has the ability to shutdown the engine via the N2 overspeed protection system - this is separate from the aircraft run/cutoff signal, although it uses the same HPSOV to effect the shutdown. That same system is used by TCMA to shutoff fuel if it determines the engine is 'running away'.
Hint, you might try going back a few pages and reading where all this has been posted previously.
TCMA (not TCAM) - Thrust Control Malfunction Accommodation - is a FADEC based system. It's resident in the engine FADEC (aka EEC) - the ONLY inputs from the aircraft that go into the TCMA is air/ground (to enable) and thrust lever position (to determine if the engine is doing what it's being commanded to do. The FADEC has the ability to shutdown the engine via the N2 overspeed protection system - this is separate from the aircraft run/cutoff signal, although it uses the same HPSOV to effect the shutdown. That same system is used by TCMA to shutoff fuel if it determines the engine is 'running away'.
Hint, you might try going back a few pages and reading where all this has been posted previously.
I hope I never suggested you guys are idiots! I very much doubt that indeed. You cannot be idiots. Planes fly, very reliably. That's evidence enough.
Maybe my analysis is simplistic, but for someone who knows as little about the nuts and bolts that are your profession, I think I'm not doing too badly.
I believe I have made a number of worthy contributions to this thread. Maybe I'm deluded. Too bad. Fact is, over the history of modern aviation, there have been a number of serious design stuff ups that "shouldn't have happened". As far as I'm concerned, the crash of AF447 is bloody good evidence of not considering a very simple, fundamental failure, and should NEVER have happened. The thing is, that would have been sooo easy to avoid. So please, don't get on too high a horse over this.
Thanks for your information about all the fuel control valves. That's cool. Yes, my cars have numerous such systems, from the radiator grilles backward.
And you misunderstand what I meant about "complicates things". Was that deliberate? What I meant was it complicates understanding how a major electrical failure could cause the Fuel Cutoff valves to close, that's all. The valves don't close if unpowered, but if the control is via the FADEC, then what could have caused them to close?
Your explanation of how the Fuel Valves are controlled is rather simplistic too. "The pilot moves a switch, that provides electrical signals to the spar valve and the engine fuel valve to open or close." Seriously? Am I an idiot then? Is it a single pole, single throw switch? Is the valve driven by a stepper motor, or what? A DC Motor and worm drive? Does it have an integral controller? How does the valve drive know when to stop at end of travel? Would you mind elaborating, please?
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2025-06-15T20:10:00
permalink Post: 11902783
TCMA is on both the Trent 1000 and GEnx-1B 'basic' - it was required for certification. There is no reason for TCMA to be listed in the MMEL as the only 'functional' portion is the via the electronic overspeed protection system (which is required for dispatch - no MEL relief) - the rest is software resident in the FADEC.
Where does that piece of software reside by the way?