June 14, 2025, 20:48:00 GMT
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.
June 14, 2025, 21:11:00 GMT
permalink Post: 11901834
Long story short. Something or someone disrupted the fuel supply on both engines simultaneously around rotation time. In a way that a line check captain could not correct it in 10+ seconds remaining flight time. Occam razor at this stage would say, that both fire handles were activated. Hope that the investigation comes up with something different.
June 14, 2025, 21:27:00 GMT
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.
June 14, 2025, 22:05:00 GMT
permalink Post: 11901881
Indeed
Thanks for answering the question I hadn't yet asked but wanted to confirm!
I'm still sticking with "Major Electrical Fault" as my most likely cause, and this adds to my suspicions.
As I understand it, the landing gear is raised / retracted by electric motor-driven hydraulic pump (pumps?). This/these would create a significant electrical load.
If the plane's multi-redundant electrical system has a fault which is intermittent (the worst kind of electrical issue to diagnose), and which causes the redundancy controls to go haywire (as there are, of course, electronic controls to detect failures and drive the switching over of primary and backup electrical supplies), then this fault could to triggered by a large load coming on-line. It could even be as simple as a high current cable lug not having been tightened when a part was being replaced at some stage. The relevant bolt might be only finger-tight. Enough to work 99.99% of the time between then and now... But a little bit more oxidation, and particularly, a bit more heat (it was a hot day), and suddenly, a fault.
Having worked in electronics for years, I know that semi-conductors (and lots of other components, especially capacitors [and batteries]) can also degrade instead of failing completely. Electro-static discharges are great for causing computer chips to die, or go meta-stable - meaning they can get all knotted up and cease working correctly - until they are powered off for a while. They can also degrade in a way that means they work normally a low temperatures, but don't above a certain temperature.
Anyway, there MUST be ways that the redundant power supplies can be brought down, simply because, to have a critical bus powered from a number of independent sources, there must be "controls" of some sort. I don't know how it's done in the 787, but that's where I'd be looking.
As there is a lot of discussion already about how the bogies are hanging the wrong way suggesting a started but failed retraction operation, and it's now confirmed that the retraction would normally have taken place at about the point where the flight went "pear shaped", I'm going to suggest that the two things are connected. More than that: I'll suggest that the Gear Up command triggered the fault that caused both engines to shut down in very short succession. Nothing the pilots did wrong, and no way they could have known and prevented it.
It's going to be difficult to prove though.
I'm still sticking with "Major Electrical Fault" as my most likely cause, and this adds to my suspicions.
As I understand it, the landing gear is raised / retracted by electric motor-driven hydraulic pump (pumps?). This/these would create a significant electrical load.
If the plane's multi-redundant electrical system has a fault which is intermittent (the worst kind of electrical issue to diagnose), and which causes the redundancy controls to go haywire (as there are, of course, electronic controls to detect failures and drive the switching over of primary and backup electrical supplies), then this fault could to triggered by a large load coming on-line. It could even be as simple as a high current cable lug not having been tightened when a part was being replaced at some stage. The relevant bolt might be only finger-tight. Enough to work 99.99% of the time between then and now... But a little bit more oxidation, and particularly, a bit more heat (it was a hot day), and suddenly, a fault.
Having worked in electronics for years, I know that semi-conductors (and lots of other components, especially capacitors [and batteries]) can also degrade instead of failing completely. Electro-static discharges are great for causing computer chips to die, or go meta-stable - meaning they can get all knotted up and cease working correctly - until they are powered off for a while. They can also degrade in a way that means they work normally a low temperatures, but don't above a certain temperature.
Anyway, there MUST be ways that the redundant power supplies can be brought down, simply because, to have a critical bus powered from a number of independent sources, there must be "controls" of some sort. I don't know how it's done in the 787, but that's where I'd be looking.
As there is a lot of discussion already about how the bogies are hanging the wrong way suggesting a started but failed retraction operation, and it's now confirmed that the retraction would normally have taken place at about the point where the flight went "pear shaped", I'm going to suggest that the two things are connected. More than that: I'll suggest that the Gear Up command triggered the fault that caused both engines to shut down in very short succession. Nothing the pilots did wrong, and no way they could have known and prevented it.
It's going to be difficult to prove though.
June 14, 2025, 22:17:00 GMT
permalink Post: 11901893
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
1) TCMA activation shutdown the engines
or
2) The fuel cutoff switches were activated.
I literally can come up with no other plausible scenarios
June 14, 2025, 22:19:00 GMT
permalink Post: 11901899
I'm still sticking with "Major Electrical Fault" as my most likely cause, and this adds to my suspicions.
[snip]
Anyway, there MUST be ways that the redundant power supplies can be brought down, simply because, to have a critical bus powered from a number of independent sources, there must be "controls" of some sort. I don't know how it's done in the 787, but that's where I'd be looking.
As there is a lot of discussion already about how the bogies are hanging the wrong way suggesting a started but failed retraction operation, and it's now confirmed that the retraction would normally have taken place at about the point where the flight went "pear shaped", I'm going to suggest that the two things are connected. More than that: I'll suggest that the Gear Up command triggered the fault that caused both engines to shut down in very short succession. Nothing the pilots did wrong, and no way they could have known and prevented it.
[snip]
Anyway, there MUST be ways that the redundant power supplies can be brought down, simply because, to have a critical bus powered from a number of independent sources, there must be "controls" of some sort. I don't know how it's done in the 787, but that's where I'd be looking.
As there is a lot of discussion already about how the bogies are hanging the wrong way suggesting a started but failed retraction operation, and it's now confirmed that the retraction would normally have taken place at about the point where the flight went "pear shaped", I'm going to suggest that the two things are connected. More than that: I'll suggest that the Gear Up command triggered the fault that caused both engines to shut down in very short succession. Nothing the pilots did wrong, and no way they could have known and prevented it.
June 14, 2025, 22:21:00 GMT
permalink Post: 11901900
I think it needs to be said again that pretty much anything can happen to the aircraft systems and the engines will carry on running - this is by design as they have independent FADEC and power supplies and at sea level fuel will get through without boost pumps. You could almost saw the wing off the fuselage and the engine would still produce thrust, TCMA notwithstanding.
We don\x92t know yet what actually triggered the RAT from the relatively short list but every item on it means there is a serious/critical failure(s). The flight path suggests that it was a double engine failure or shutdown (commanded or uncommanded) as anything else should have left the aeroplane in a poor state but able to climb away.
We don\x92t know yet what actually triggered the RAT from the relatively short list but every item on it means there is a serious/critical failure(s). The flight path suggests that it was a double engine failure or shutdown (commanded or uncommanded) as anything else should have left the aeroplane in a poor state but able to climb away.
June 14, 2025, 22:24:00 GMT
permalink Post: 11901903
OK, but even if we do assume that there was a major electrical fault which brought down the main supplies: multiple posts in this thread have already asserted that this would not cause the shutdown of the engines, and that even if the fuel pumps failed, suction would keep the engines running.
June 14, 2025, 22:26:00 GMT
permalink Post: 11901906
I am curious to learn what power source drives the high-pressure fuel pumps in the engine. If there is such a thing, I suppose there would.
Gearbox? This is at odds with a possible cascading electric failure that (might have) caused a loss of engine fuel feed.
To my understanding on my ancient plane and engine design, the HP pumps that feed the nozzles are driven mechanically, which enables gravity feeding among other scenarios, but also assures the fuel supply is independent of whatever happens upstream of the nacelle. Except for LP/fire shut-off cocks.
Gearbox? This is at odds with a possible cascading electric failure that (might have) caused a loss of engine fuel feed.
To my understanding on my ancient plane and engine design, the HP pumps that feed the nozzles are driven mechanically, which enables gravity feeding among other scenarios, but also assures the fuel supply is independent of whatever happens upstream of the nacelle. Except for LP/fire shut-off cocks.
June 14, 2025, 22:33:00 GMT
permalink Post: 11901909
June 14, 2025, 22:34:00 GMT
permalink Post: 11901910
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.
1) TCMA activation shutdown the engines
or
2) The fuel cutoff switches were activated.
I literally can come up with no other plausible scenarios.
Am I right in saying, from a mathmatical perspective, that dual engine flame out due biocide overdose would be more likely than a TCMA activation shutting down the engines? Considering we have examples of engines reducing to idle within seconds of each other in the past, but we have no examples of airborne TCMA issues I would have thought this to be the case. Likewise, nefarious intent also appears more likely statistically than a TCMA issue.
I have high-school level statistics under my belt so I pose that as a question for people much smarter than myself.
June 14, 2025, 22:39:00 GMT
permalink Post: 11901913
Almost all catastrophic accidents that are not deliberately initiated require multiple causes. It’s extremely unlikely that both engine condition switches or fire switches were accidentaly actuated during a routine rotation and initial climb. However it’s stil possible that the crew did actuate those switches (intentionally or unintentionally) in response to some anomaly experienced at that time. Thus it’s not impossible that electrical system malfunction was the first link in a sequence that led to removing the fuel supply to both engines. The most obvious one is that crew thought that they had dual engine failure due to lost of main electrical power and initiated a double engine restart bycling the engine condition levers.
The purpose of this post is not to promote the above as a possible cause of the accident, but to remaind people that a (proven) mechanical fault does not rule out pilot error and vice versa.
The purpose of this post is not to promote the above as a possible cause of the accident, but to remaind people that a (proven) mechanical fault does not rule out pilot error and vice versa.
June 14, 2025, 23:04:00 GMT
permalink Post: 11901940
If you are referring to loss of all boost pumps, am not aware of any engine that will not continue to run with a suction feed to the main boost pumps at low altitudes. At high altitudes, there is a chance of cavitation of the main pumps but only at very high powers, and generally not at sea level.
June 14, 2025, 23:05:00 GMT
permalink Post: 11901941
I am curious to learn what power source drives the high-pressure fuel pumps in the engine. If there is such a thing, I suppose there would.
Gearbox? This is at odds with a possible cascading electric failure that (might have) caused a loss of engine fuel feed.
To my understanding on my ancient plane and engine design, the HP pumps that feed the nozzles are driven mechanically, which enables gravity feeding among other scenarios, but also assures the fuel supply is independent of whatever happens upstream of the nacelle. Except for LP/fire shut-off cocks.
Gearbox? This is at odds with a possible cascading electric failure that (might have) caused a loss of engine fuel feed.
To my understanding on my ancient plane and engine design, the HP pumps that feed the nozzles are driven mechanically, which enables gravity feeding among other scenarios, but also assures the fuel supply is independent of whatever happens upstream of the nacelle. Except for LP/fire shut-off cocks.
Engine driven fuel pump failures are very rare, but have happened (usually with some 'precursor' symptoms that were ignored or mis-diagnosed by maintenance). It would be unheard of for engine driven fuel pumps to fail on both engines on the same flight.
As I've repeatedly posted, even a 100% aircraft power failure would not explain both engines quitting, at least without several other existing faults. Again, never say never, but you can only combine so many 10-9 events before it becomes ridiculous...
TCMA doesn't know what V1 is - it's active whenever the air/ground logic says the aircraft is on-ground.
June 14, 2025, 23:20:00 GMT
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) ...
June 14, 2025, 23:30:00 GMT
permalink Post: 11901954
If you are referring to loss of all boost pumps, am not aware of any engine that will not continue to run with a suction feed to the main boost pumps at low altitudes. At high altitudes, there is a chance of cavitation of the main pumps but only at very high powers, and generally not at sea level.
Speculating on a combined loss of electric power plus bad fuel, but seems as likely as any of the other farfetched scenarios.
June 14, 2025, 23:40:00 GMT
permalink Post: 11901962
Howdy
I am curious to learn what power source drives the high-pressure fuel pumps in the engine. If there is such a thing, I suppose there would.
Gearbox? This is at odds with a possible cascading electric failure that (might have) caused a loss of engine fuel feed.
To my understanding on my ancient plane and engine design, the HP pumps that feed the nozzles are driven mechanically, which enables gravity feeding among other scenarios, but also assures the fuel supply is independent of whatever happens upstream of the nacelle. Except for LP/fire shut-off cocks.
Gearbox? This is at odds with a possible cascading electric failure that (might have) caused a loss of engine fuel feed.
To my understanding on my ancient plane and engine design, the HP pumps that feed the nozzles are driven mechanically, which enables gravity feeding among other scenarios, but also assures the fuel supply is independent of whatever happens upstream of the nacelle. Except for LP/fire shut-off cocks.
There have been conflicting reports about the call to ATC. Original reports quoted the Captain saying "Mayday...no thrust, losing power, cannot lift". But I've seen reports today stating the call was simply "Mayday, Mayday" and then no further response.
Difficult to confirm so I wouldn't put too much weight behind it until something more official is released.
Difficult to confirm so I wouldn't put too much weight behind it until something more official is released.
June 15, 2025, 00:08:00 GMT
permalink Post: 11901978
Lull
Consider losing one engine on the Dream. If it is a generator that's failed let's say #2 . Do the electric fuel pumps lose power? Only in #2? Does the mechanical pump start feeding right away? If so, is there a lull? Are both engines fuel pumps supplied off one Gen?
See I think there was no simultaneous loss of both 1, 2.
The odds give me a migraine. I still wonder if TCMA knows the difference between parked, rolling, rotated brakes and stowed. Only parenthetically, it didn't do this
See I think there was no simultaneous loss of both 1, 2.
The odds give me a migraine. I still wonder if TCMA knows the difference between parked, rolling, rotated brakes and stowed. Only parenthetically, it didn't do this
June 15, 2025, 00:54:00 GMT
permalink Post: 11902008
I think it needs to be said again that pretty much anything can happen to the aircraft systems and the engines will carry on running - this is by design as they have independent FADEC and power supplies and at sea level fuel will get through without boost pumps. You could almost saw the wing off the fuselage and the engine would still produce thrust, TCMA notwithstanding.
Anyway, the thing I'm looking at is how the fuel cutoff switch function could have been activated in some other way. To me, it seems obvious that there are wires that run between the engine fuel shutoff valves and the cockpit / flight control panel (no doubt with relays etc in between). I don't know where those shutoff valves are located, but logic says they should be located in the fuselage, not out at the engines. I also don't know how those valves operate - are they solenoid valves or electro-mechanically driven? Nor do I know where the power to activate those valves comes from, but using my logic, if those valves close when powered off, such as solenoid valves typically do, then the power cannot exclusively come from the engine-dedicated generators. If it did, you'd never be able to start the engines so they could supply their own power to hold those valves open. So, there must be some power (appropriately) fed from the main aircraft control bus to activate those valves - if the rest of what I'm assuming is correct. Anyway, like I say, I don't know enough about the details at this point, but there are many more ways to activate or deactivate a circuit than by flicking a switch. Killing the relevant power supply, for example. A screwdriver across some contacts (for example), another. Shorting a wire to Chassis, maybe. Just trying to contribute what I can.
You raise another interesting point: "TCMA notwithstanding". Could you elaborate, please? What will happen if the TCMA system, which apparently also has some degree of engine control, loses power? The problem with interlinked circuits and systems is that sometimes, unexpected things can happen when events that were not considered actually happen. If one module, reporting to another, loses power or fails, sometimes it can "tell" the surviving module something that isn't true... My concern is where does the power to the Fuel Cutoff switches come from? Are there relays or solid-state switches (or what?) between the Panel Switches and the valves? If so, is the valve power derived from a different source, and if so, where? Are the valves solenoids, open when power applied, or something else? What is the logic involved, between switch and valve?
Would you mind answering these questions so I can ponder it all further, please? If I'm wrong, I'll happily say so.
We don\x92t know yet what actually triggered the RAT from the relatively short list but every item on it means there is a serious/critical failure(s). The flight path suggests that it was a double engine failure or shutdown (commanded or uncommanded) as anything else should have left the aeroplane in a poor state but able to climb away.
June 15, 2025, 01:21:00 GMT
permalink Post: 11902026
I can buy the AC power loss, but TCMA activation as well - That\x92s a stretch. TCMA is available on the ground and on approach and will activate if the engine thrust doesn\x92t follow the Thrust Lever command. On the ground it will shut the engine down (think RTO with engine stuck at T/O). On approach it will reduce the thrust if the engine doesn\x92t respond to the Thrust Lever command ala Cathay Pacific A330 (CMB - HKG) with the fuel contamination incident.