ams6110
2025-06-13T17:31:00
permalink Post: 11900723

Quote:

Originally Posted by andihce

\xb7 It is difficult to understand a dual engine rollback. Various causes have been suggested but ruled \x93unlikely\x94 here. However, it is not possible to rule out a unicorn event, like the dual engine rollback experienced by BA 38. Leaving aside the cause, it is useful to look at the consequences.
.

Air crashes are "unlikely" a priori. Therefore I think the root cause, when determined, will be something unlikely. Best case, we learn something practical that can be mitigated in the future.

Subjects: None

1 user liked this post.

ams6110
2025-06-13T20:23:00
permalink Post: 11900870

Quote:

Originally Posted by overstress

Yet credence is given here to his recollection of a bang and green lights etc, yet his comments about THRUST increasing are ignored by the RAT theorists\x85

In fairness, recalling a "green light" is a pretty specific thing. A "sensation of thrust" from a seated passenger who may not even be an experienced flyer could be describing any feeling of movement or the illusion of same.

Subjects: RAT (All)

4 users liked this post.

ams6110
2025-06-14T23:30:00
permalink Post: 11901954

Quote:

Originally Posted by fdr

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.

Would the suction feed work if the fuel filters were clogged due to contaminated fuel? Boost pumps will bypass clogged filters but what about suction pumps?

Speculating on a combined loss of electric power plus bad fuel, but seems as likely as any of the other farfetched scenarios.

Subjects: Fuel (All) Fuel Pumps

ams6110
2025-06-15T20:33:00
permalink Post: 11902798

Quote:

Originally Posted by C2H5OH

Voltage fluctuation can have very nasty effects on electronics and sensors. There is a hacking technique called "voltage glitching" which makes use of these effects to trick electronics in states they are not designed for and never supposed to be.
So I wouldn't vouch for the FADECs if there was catastrophic problem with the power distribution in the aircraft.

Except as I understand it from tdracer and other posts, the FADECs are self-powered. The "FA" stands for Fully Autonomous. Whatever happens on the other electrical systems is (by design) completely isolated.

Subjects: None

ams6110
2025-06-15T20:43:00
permalink Post: 11902809

Quote:

Originally Posted by Alty7x7

FADEC = Full-Authority Digital Engine Control

Isolation comment still applies, but 'completely' may be debatable when there are still physical connections.

Well even when I think I know something I get it wrong. Thanks for the correction. Back to reader mode.

Subjects: FADEC

3 users liked this post.

ams6110
2025-06-19T18:48:00
permalink Post: 11906263

Quote:

Originally Posted by CloudChasing

I\x92m sure this is wrong; was looking for confirmation. I read somewhere that the 787 keeps the fuel valve open by an electric driven actuator, and closes it by spring force.

tdracer addressed the shutoff valve operation earlier: "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). "

Subjects: Fuel (All) Fuel Cutoff High Pressure Shutoff Valve

4 users liked this post.

ams6110
2025-06-19T23:04:00
permalink Post: 11906466

Quote:

Originally Posted by MatthiasC172

I am pretty sure that with WoW and >=85 kt a throttle being pulled to idle leads to immediate max autobrake plus speed-brake/spoilers deployment. I don’t see an option there to trigger TCMA like this but happy to learn from someone with more experience.

SLF but I think this makes sense. If pulling from takeoff thust back to idle with WoW would cause TCMA activation, we'd see engine shutdowns on every rejected takeoff.

I also wonder about this theory that one of the pilots called for reject and pulled the thrust levers back, and the other overruled him and continued the takeoff. Is this plausible? CRM aside, if max braking and spoilers are triggered in this scenario, it doesn't seem so to me.

Last edited by ams6110; 19th Jun 2025 at 23:15 . Reason: typo correction

Subjects: TCMA (Activation) TCMA (All)

ams6110
2025-06-20T16:51:00
permalink Post: 11907131

Quote:

Originally Posted by bbofh

... The generally held theory for each engine\x92s FADEC failure (due to a common software error related to a ground-air sensing failure) is not supported by the cumulative hours over many years without such a failure. So, if you then look around for another component that can shut down two engines simultaneously you end up with the fuel shut-off valves (FSOV). Why? On each engine It is fail-safed to close off fuel-feed flows by a spring that is held open by a solenoid. If that solenoid loses electrical power, the FSOV closes and the engine shuts down after a short period.

Are you certain of that? Because tdracer (and perhaps others) have asserted that the valves are latching, and must be powered on OR off, precisely so that an electrical power loss does not close the valve (and shut down the engine).

Subjects: Dual Engine Failure Engine Failure (All) FADEC

18 users liked this post.

ams6110
2025-06-21T16:35:00
permalink Post: 11907894

Quote:

Originally Posted by GroundedSpanner

...
But there was only so much 'good' fuel in the lines. The engines sucking fuel themselves, the fuel would now be coming from the suction pickups, a different supply. A supply likely heavily water contaminated. It would take a few seconds for that contaminated fuel to actually reach the engines, but when that contaminated fuel hit, Thrust would have been significantly reduced. The EEC's would have been doing their best to maintain the thrust, firewalling the throttles would probably have little effect at that exact moment. The engines would have likely worked through that bad fuel in a shortish period of time, but a period of time that our crew did not have. A fully loaded aircraft producing less than take-off thrust, is not sustaining enough thrust for continued flight. The rest - is down to the skill of the crew in deciding exactly where to hit the ground within the very narrow range of choice they had.

In this scenario would we expect to see smoke/steam from the engines as they digested this heavy water contamination?

Subjects: None

1 user liked this post.

ams6110 2025-06-13T17:31:00 permalink Post: 11900723	Quote: Originally Posted by andihce \xb7 It is difficult to understand a dual engine rollback. Various causes have been suggested but ruled \x93unlikely\x94 here. However, it is not possible to rule out a unicorn event, like the dual engine rollback experienced by BA 38. Leaving aside the cause, it is useful to look at the consequences. . Air crashes are "unlikely" a priori. Therefore I think the root cause, when determined, will be something unlikely. Best case, we learn something practical that can be mitigated in the future. Subjects: None 1 user liked this post.
ams6110 2025-06-13T20:23:00 permalink Post: 11900870	Quote: Originally Posted by overstress Yet credence is given here to his recollection of a bang and green lights etc, yet his comments about THRUST increasing are ignored by the RAT theorists\x85 In fairness, recalling a "green light" is a pretty specific thing. A "sensation of thrust" from a seated passenger who may not even be an experienced flyer could be describing any feeling of movement or the illusion of same. Subjects: RAT (All) 4 users liked this post.
ams6110 2025-06-14T23:30:00 permalink Post: 11901954	Quote: Originally Posted by fdr 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. Would the suction feed work if the fuel filters were clogged due to contaminated fuel? Boost pumps will bypass clogged filters but what about suction pumps? Speculating on a combined loss of electric power plus bad fuel, but seems as likely as any of the other farfetched scenarios. Subjects: Fuel (All) Fuel Pumps
ams6110 2025-06-15T20:33:00 permalink Post: 11902798	Quote: Originally Posted by C2H5OH Voltage fluctuation can have very nasty effects on electronics and sensors. There is a hacking technique called "voltage glitching" which makes use of these effects to trick electronics in states they are not designed for and never supposed to be. So I wouldn't vouch for the FADECs if there was catastrophic problem with the power distribution in the aircraft. Except as I understand it from tdracer and other posts, the FADECs are self-powered. The "FA" stands for Fully Autonomous. Whatever happens on the other electrical systems is (by design) completely isolated. Subjects: None
ams6110 2025-06-15T20:43:00 permalink Post: 11902809	Quote: Originally Posted by Alty7x7 FADEC = Full-Authority Digital Engine Control Isolation comment still applies, but 'completely' may be debatable when there are still physical connections. Well even when I think I know something I get it wrong. Thanks for the correction. Back to reader mode. Subjects: FADEC 3 users liked this post.
ams6110 2025-06-19T18:48:00 permalink Post: 11906263	Quote: Originally Posted by CloudChasing I\x92m sure this is wrong; was looking for confirmation. I read somewhere that the 787 keeps the fuel valve open by an electric driven actuator, and closes it by spring force. tdracer addressed the shutoff valve operation earlier: "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).* " Subjects: Fuel (All) Fuel Cutoff High Pressure Shutoff Valve 4 users liked this post.
ams6110 2025-06-19T23:04:00 permalink Post: 11906466	Quote: Originally Posted by MatthiasC172 I am pretty sure that with WoW and >=85 kt a throttle being pulled to idle leads to immediate max autobrake plus speed-brake/spoilers deployment. I don’t see an option there to trigger TCMA like this but happy to learn from someone with more experience. SLF but I think this makes sense. If pulling from takeoff thust back to idle with WoW would cause TCMA activation, we'd see engine shutdowns on every rejected takeoff. I also wonder about this theory that one of the pilots called for reject and pulled the thrust levers back, and the other overruled him and continued the takeoff. Is this plausible? CRM aside, if max braking and spoilers are triggered in this scenario, it doesn't seem so to me. Last edited by ams6110; 19th Jun 2025 at 23:15 . Reason: typo correction Subjects: TCMA (Activation) TCMA (All)
ams6110 2025-06-20T16:51:00 permalink Post: 11907131	Quote: Originally Posted by bbofh ... The generally held theory for each engine\x92s FADEC failure (due to a common software error related to a ground-air sensing failure) is not supported by the cumulative hours over many years without such a failure. So, if you then look around for another component that can shut down two engines simultaneously you end up with the fuel shut-off valves (FSOV). Why? On each engine It is fail-safed to close off fuel-feed flows by a spring that is held *open* by a solenoid. If that solenoid loses electrical power, the FSOV closes and the engine shuts down after a short period. Are you certain of that? Because tdracer (and perhaps others) have asserted that the valves are latching, and must be powered on OR off, precisely so that an electrical power loss does not close the valve (and shut down the engine). Subjects: Dual Engine Failure Engine Failure (All) FADEC 18 users liked this post.
ams6110 2025-06-21T16:35:00 permalink Post: 11907894	Quote: Originally Posted by GroundedSpanner ... But there was only so much 'good' fuel in the lines. The engines sucking fuel themselves, the fuel would now be coming from the suction pickups, a different supply. A supply likely heavily water contaminated. It would take a few seconds for that contaminated fuel to actually reach the engines, but when that contaminated fuel hit, Thrust would have been significantly reduced. The EEC's would have been doing their best to maintain the thrust, firewalling the throttles would probably have little effect at that exact moment. The engines would have likely worked through that bad fuel in a shortish period of time, but a period of time that our crew did not have. A fully loaded aircraft producing less than take-off thrust, is not sustaining enough thrust for continued flight. The rest - is down to the skill of the crew in deciding exactly where to hit the ground within the very narrow range of choice they had. In this scenario would we expect to see smoke/steam from the engines as they digested this heavy water contamination? Subjects: None 1 user liked this post.

Posts by user "ams6110" [Posts: 9 Total up-votes: 31 Pages: 1]