OldnGrounded
June 15, 2025, 13:29:00 GMT
permalink Post: 11902475

Quote:

Originally Posted by blind pew

World wide grounding of the DC10 fleet after Chicago where maintenance had modified engine removal procedures which led to a wing engine loss taking out hydraulic systems that allowed the slats to retract ..aircraft stalled asymetrically and rolled inverted. Many other aircraft had damaged mounts/bolts not all were reported.

AA191. The NTSB report with probable cause was published within less than a year, IIRC. But it wasn't all that difficult to determine once they knew that forklifts were being used to R&R engines. In the 737 rudder hardovers, I think eight years passed between the first crash and a probable cause finding (in the second crash) that implicated the PCU servo. Of course, as someone has already posted, much more monitoring, data recording and transmission is available now in 21st century aircraft, although the accident aircraft in this case may not have transmitted much in the time available.

Last edited by OldnGrounded; 15th June 2025 at 13:37 . Reason: Typo. to not yo

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Hydraulic Failure (All) NTSB

OldnGrounded
June 15, 2025, 13:34:00 GMT
permalink Post: 11902477

Quote:

Originally Posted by Pelican

Trying to keep an open mind, but\x85.

Is no one surprised the lone survivor remembers a bang just before impact, and other things like apparently emergency lights, but has not mentioned the power going from takeoff power to nothing. Even the power change at thrust reduction altitude is often very noticeable in the cabin, so it surprises me nothing about the noise (and startle/panic) of full-power to no-power has been mentioned. I think we are getting into absurd scenarios trying to make the scenario of a simultaneous double engine failure just after liftoff fit, based on perhaps not the best evidence.

As an expert on human memory and cognition has pointed out above (and we all more or less know), what that survivor remembers or he thinks he remembers \x97 and what we think or are told he doesn't remember \x97 cannot be considered accurate or reliable. At all.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Dual Engine Failure Engine Failure (All)

OldnGrounded
June 15, 2025, 19:07:00 GMT
permalink Post: 11902731

Quote:

Originally Posted by LTC8K6

I would guess that 787 pilot seats are electrically moved and use a worm gear drive.

I'd be surprised if they are mechanically adjusted and held in place by a pin.

They are electrically operated, and there have been known issues and incidents. See, e.g., LATAM 800. Edit: Just an old engineer, but the chances that uncommanded seat movement was causative in the AI crash seem vanishingly small.

https://en.wikipedia.org/wiki/LATAM_Airlines_Flight_800

Subjects: None

OldnGrounded
June 15, 2025, 23:28:00 GMT
permalink Post: 11902958

Quote:

Originally Posted by AirScotia

What happens if the inputs are erroneous because of a mechanical or maintenance failure?

tdracer has let us know that TCMA relies on inputs from three radio altimeters and two WoW switches and that at least one from each set must report on-ground.

Subjects: None

OldnGrounded
June 15, 2025, 23:34:00 GMT
permalink Post: 11902965

Quote:

Originally Posted by ajd1

FADEC issue I suspect.

With both engines?

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FADEC

OldnGrounded
June 15, 2025, 23:55:00 GMT
permalink Post: 11902983

Quote:

Originally Posted by DIBO

but that was on the 747-8

Ah, yes. Missed that. Thanks. But I have to assume (I know) that any responsible aviation engineers designing a system that can shut down both (all) engines simultaneously when the airplane is on the ground is going to want to make very sure that the airplane is on the ground.

But I'll check.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Dual Engine Failure Engine Failure (All)

OldnGrounded
June 16, 2025, 00:52:00 GMT
permalink Post: 11903015

Quote:

Originally Posted by tdracer

No, what I posted was the logic for the 747-8 - I simply don't know (or at least don't remember) what the TCMA air/ground logic looks like for the 787/GEnx-1B.

I've been looking and haven't found the current TCMA configuration for that engine yet. Perhaps of interest, I did find that Boeing petitioned for and received an exemption from \xa7\xa7 25.901(c) and 25.1309(b) in 2016.

Quote:

Petition for Time Limited Exemption to 14 CFR 25.901(c) at Amendment level 25-46 and 25-126 and 25.1309{b) at Amendment Level 25-41 and 25-123 for General Electric GEnx-1 B Thrust Control Malfunction Accommodation - 787 787-8, 787-9

Petition:
https://downloads.regulations.gov/FA...tachment_1.pdf
Grant of exemption:
https://downloads.regulations.gov/FA...tachment_1.pdf

I'll keep looking to find out what they actually did.

Subjects: None

OldnGrounded
June 16, 2025, 01:19:00 GMT
permalink Post: 11903028

Quote:

Originally Posted by bbofh

The TCMA patent application is at: https://patents.google.com/patent/US6704630B2/en
Quite a simple system (not)
What gets your attention is the fact that you can continue to operate the aircraft without an MMEL entry when one of the two systems (per EEC) that shadow each other... is unserviceable.
As it says: "Typically the aircraft is allowed to operate for a limited period of time with just a single operative processing subsystem."
That 787 was not long out of maintenance.

Thanks for posting this. I read it quickly and glanced at the drawings, which are adequate for the patent application but not nearly adequate to understand the system in any depth.

I note that, unless I missed it, the patent application doesn't address a mechanism for determining whether an aircraft is actually on the ground. I suppose that will depend on some of those "several other digital inputs."

Quote:

Via the execution of software package 130 , each of the processing subsystems 20 a and 20 b monitors the position of thrust lever 36 , engine power level, and several other digital inputs provided from the aircraft via digital ARINC data buses 46 .

. Emphasis added.

I'm still looking for identification of the relevant inputs for TCMA on the GEnx-1B. If anyone has suggestions, please share.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): ARINC

OldnGrounded
June 16, 2025, 01:33:00 GMT
permalink Post: 11903033

Quote:

Originally Posted by Keith.

From six paragraphs down in the TCMA patent application.

" The method of the present invention compares the engine's actual power level with a threshold contour defined by the TCMA software package. When the TCMA software package determines that a thrust control malfunction has occurred, based on the engine's power level exceeding the threshold contour, the engine is shut down by the TCMA circuit."

Right. When the aircraft is on the ground. What inputs are used to determine whether the aircraft is on the ground?

Subjects: None

OldnGrounded
June 16, 2025, 01:40:00 GMT
permalink Post: 11903037

Quote:

Originally Posted by AndyJS

This has just appeared in the Times (of London) which is usually one of the most reliable sources of information in the UK.

"A loss of engine power is emerging as the most likely cause of the crash of the Air India Boeing that killed at least 279 people at Ahmedabad on Thursday. The Boeing 787-8 series appeared to have suffered from lower than normal thrust from its General Electric GEnx engines as it took off and failed to climb more than 450ft before crashing, video and reports from the Indian authorities have indicated.The new information has eclipsed an early focus on the unusual configuration of the aircraft\x92s wing flaps and landing gear."

https://www.thetimes.com/world/asia/...rash-vhqw6b7v3

(subscription required to read the article)

Thanks for the heads up. The story also says, "No cause has yet been identified for what would be an extremely rare power loss from both engines, but on Sunday the Indian civil air authority (DGCA) began urgent pre-flight inspections of fuel systems, electronic engine controls and other systems on Indian Boeing 787s."

And it quotes Juan Browne (Blancolirio): \x93There was something terribly wrong with this 787 jet and we need to find out really quickly what went wrong because we\x92ve got a thousand of these operating today and operators need to find out what happened.\x94

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): DGCA GEnx (ALL)

OldnGrounded
June 16, 2025, 02:15:00 GMT
permalink Post: 11903057

Folks, if an interim report or other official communication from the investigation is released, it will almost certainly come from India's AAIB or at least be posted to its site. So checking there before posting something like that here would be a really good idea.

https://aaib.gov.in/

Admin note: the url is correct, app are the Government allow advertising on their sites!

SPlot

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): AAIB (All)

OldnGrounded
June 16, 2025, 03:41:00 GMT
permalink Post: 11903083

Quote:

Originally Posted by Pip_Pip

Does the article say anything about the toilet habits of bears?

Please, we really don't need any more snark in this thread. And your snark suggests that you may not understand the implications of the story cited in the posts you quoted.

That the Times reports, clearly based on information from official Indian sources, that loss of thrust in both engines was a key factor in this crash, and that DGCA has ordered urgent inspections of 787s because of preliminary findings of the investigation, is important news from one of the most responsible newspapers anywhere. And Juan Browne's urging quick action and citing the importance to the entire fleet and to aviation generally is also significant. He's a respected aviator many here pay serious attention to.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): DGCA

OldnGrounded
June 16, 2025, 03:52:00 GMT
permalink Post: 11903086

Quote:

Originally Posted by fgrieu

Among the most interesting of the Times article:

I wish we had quotes of "the Indian authorities".

Yes, so do I. But we live now in a world where information from officials who aren't quoted because they aren't authorized to speak, or are authorized but insist on anonymity, is very often the only information available, especially early in an investigation like this one. The fact that this story is in the Times gives me a fair amount of confidence that what is being reported really is from official sources. They actually have journalistic standards there.

Subjects: None

OldnGrounded
June 16, 2025, 02:15:00 GMT
permalink Post: 11903737

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): AAIB (All)

OldnGrounded
June 16, 2025, 23:49:00 GMT
permalink Post: 11903875

Quote:

Originally Posted by Lead Balloon

(I understand from the now-closed thread, that there is an unresolved question as to whether a petition for an exemption from the TCMA requirement had been successful.)

Unless I've missed another one, the relevant petition was for a time limited exemption for TCMA for the GEnx-1B. It was granted. ~~See attached~~ . Nope. Uploads failing. See here:

https://downloads.regulations.gov/FA...tachment_1.pdf

https://downloads.regulations.gov/FA...tachment_1.pdf

I haven't yet been successful in finding the details of the solution that would have brought TCMA for that engine into compliance by the 2018 deadline requested and granted.

Subjects: None

OldnGrounded
June 17, 2025, 02:42:00 GMT
permalink Post: 11903927

Quote:

Originally Posted by Lord Farringdon

[. . .] In this regard we can recall several instances of double engine failure associated with bird strikes generally involving large birds or large flocks or both. But it seems we have discounted this theory very early in discussion. Why? Because we cant see any birds, or flocks of birds or engine flames/surges or puffs of smokes from the engines which would support this. Really?
[. . .]
Edit: I might add, they would have found remains on the runway if this did indeed happen. But we have heard anything from anybody?

It seems pretty unlikely that a bird strike that took out both of those very big engines simultaneously would not have been fairly obvious in ways that nearby observers (e.g., the crew, ATC, airport personnel?) would have noticed. Possible, of course, but I don't think we've seen any evidence that points in that direction. Also, for what it's worth, the Times of London June 15 story " New clues point to engine failure for cause of Air India plane crash " cited here in the closed thread includes this:

Quote:

The Indian authorities indicated that a bird strike has been ruled out.

A poster in the closed thread pointed out, properly I think, that the Times shouldn't be relied upon for presentation or interpretation of technical information. Like most general news organizations, their reporters and editors (mostly) just don't have the background to assess, filter and explain complex processes and technology. Unlike many, though, the Times can generally be relied upon to seek appropriate sources and report accurately what those sources say. I think it's very likely that Indian authorities have ruled out a bird strike, and I also think those authorities are competent to make that decision.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Dual Engine Failure Engine Failure (All)

OldnGrounded
June 17, 2025, 03:02:00 GMT
permalink Post: 11903932

Quote:

Originally Posted by Lead Balloon

Back to the subject of the TCMA, in order for the four channels (A and B for engine 1 and A and B for engine 2) to be truly independent, there would have to be, for example, four, separate weight on wheels sensors and two, separate throttle position sensors per throttle. I would be extraordinarily surprised if that's what has been implemented, but will happily stand correct.

And a sensor per channel per engine for actual thrust, and sensor inputs in addition to WoW switches to validate on-ground state (perhaps radio altimeters, as described by tdracer for some of the 74s, which I misread as 787s). I, too would be surprised \x97 stunned \x97 if all of that had been implemented. I really want to know what exactly was implemented, and when and in which specific airplanes/engines. What I expect, though, is that when we learn all of that, we'll decide that it really is exceedingly unlikely that TCMA shut down those engines in Ahmedabad the other day. But it sure looks like something did.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Weight on Wheels

OldnGrounded
June 17, 2025, 03:34:00 GMT
permalink Post: 11903943

Quote:

Originally Posted by dragon6172

There are eight air ground sensors. Two truck tilt sensors and two strut compression sensors on each main gear.

Thanks. Do we know that these are monitored by TCMA for air/ground state and if so, do we know the logic used to make a determination based on those inputs? Alternatively, do you know where we should be looking for those answers?

Subjects: None

OldnGrounded
June 17, 2025, 04:05:00 GMT
permalink Post: 11903952

Quote:

Originally Posted by dragon6172

No idea. I only got that info from the Master MEL on the FAA website. According to the MMEL the aircraft can be dispatched as long as there is one of each type sensor working on each main gear. (AIs MEL could be more restrictive)

Thanks again. Yes, I checked the MMEL too. ~~It also says that the aircraft may be dispatched with one of two TCMA functions operational~~ . Edit: dragon6172 has pointed out that the cited MMEL entry for TCMA applies to Rolls Royce engines, so not relevant here.

Last edited by OldnGrounded; 17th June 2025 at 05:06 .

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FAA MEL

OldnGrounded
June 17, 2025, 05:03:00 GMT
permalink Post: 11903972

Quote:

Originally Posted by dragon6172

Pretty sure that the (RR) after that TCMA entry means it is only applicable to Rolls Royce engines. I believe the accident aircraft had GE engines?

Ah, you're right. Didn't notice. And the accident aircraft did have GE engines. Thanks.

Subjects: None

OldnGrounded June 15, 2025, 13:29:00 GMT permalink Post: 11902475	Quote: Originally Posted by blind pew World wide grounding of the DC10 fleet after Chicago where maintenance had modified engine removal procedures which led to a wing engine loss taking out hydraulic systems that allowed the slats to retract ..aircraft stalled asymetrically and rolled inverted. Many other aircraft had damaged mounts/bolts not all were reported. AA191. The NTSB report with probable cause was published within less than a year, IIRC. But it wasn't all that difficult to determine once they knew that forklifts were being used to R&R engines. In the 737 rudder hardovers, I think eight years passed between the first crash and a probable cause finding (in the second crash) that implicated the PCU servo. Of course, as someone has already posted, much more monitoring, data recording and transmission is available now in 21st century aircraft, although the accident aircraft in this case may not have transmitted much in the time available. Last edited by OldnGrounded; 15th June 2025 at 13:37 . Reason: Typo. to not yo Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Hydraulic Failure (All) NTSB
OldnGrounded June 15, 2025, 13:34:00 GMT permalink Post: 11902477	Quote: Originally Posted by Pelican Trying to keep an open mind, but\x85. Is no one surprised the lone survivor remembers a bang just before impact, and other things like apparently emergency lights, but has not mentioned the power going from takeoff power to nothing. Even the power change at thrust reduction altitude is often very noticeable in the cabin, so it surprises me nothing about the noise (and startle/panic) of full-power to no-power has been mentioned. I think we are getting into absurd scenarios trying to make the scenario of a simultaneous double engine failure just after liftoff fit, based on perhaps not the best evidence. As an expert on human memory and cognition has pointed out above (and we all more or less know), what that survivor remembers or he thinks he remembers \x97 and what we think or are told he doesn't remember \x97 cannot be considered accurate or reliable. At all. Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Dual Engine Failure Engine Failure (All)
OldnGrounded June 15, 2025, 19:07:00 GMT permalink Post: 11902731	Quote: Originally Posted by LTC8K6 I would guess that 787 pilot seats are electrically moved and use a worm gear drive. I'd be surprised if they are mechanically adjusted and held in place by a pin. They are electrically operated, and there have been known issues and incidents. See, e.g., LATAM 800. Edit: Just an old engineer, but the chances that uncommanded seat movement was causative in the AI crash seem vanishingly small. https://en.wikipedia.org/wiki/LATAM_Airlines_Flight_800 Subjects: None
OldnGrounded June 15, 2025, 23:28:00 GMT permalink Post: 11902958	Quote: Originally Posted by AirScotia What happens if the inputs are erroneous because of a mechanical or maintenance failure? tdracer has let us know that TCMA relies on inputs from three radio altimeters and two WoW switches and that at least one from each set must report on-ground. Subjects: None
OldnGrounded June 15, 2025, 23:34:00 GMT permalink Post: 11902965	Quote: Originally Posted by ajd1 FADEC issue I suspect. With both engines? Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FADEC
OldnGrounded June 15, 2025, 23:55:00 GMT permalink Post: 11902983	Quote: Originally Posted by DIBO but that was on the 747-8 Ah, yes. Missed that. Thanks. But I have to assume (I know) that any responsible aviation engineers designing a system that can shut down both (all) engines simultaneously when the airplane is on the ground is going to want to make very sure that the airplane is on the ground. But I'll check. Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Dual Engine Failure Engine Failure (All)
OldnGrounded June 16, 2025, 00:52:00 GMT permalink Post: 11903015	Quote: Originally Posted by tdracer No, what I posted was the logic for the 747-8 - I simply don't know (or at least don't remember) what the TCMA air/ground logic looks like for the 787/GEnx-1B. I've been looking and haven't found the current TCMA configuration for that engine yet. Perhaps of interest, I did find that Boeing petitioned for and received an exemption from \xa7\xa7 25.901(c) and 25.1309(b) in 2016. Quote: Petition for Time Limited Exemption to 14 CFR 25.901(c) at Amendment level 25-46 and 25-126 and 25.1309{b) at Amendment Level 25-41 and 25-123 for General Electric GEnx-1 B Thrust Control Malfunction Accommodation - 787 787-8, 787-9 Petition: https://downloads.regulations.gov/FA...tachment_1.pdf Grant of exemption: https://downloads.regulations.gov/FA...tachment_1.pdf I'll keep looking to find out what they actually did. Subjects: None
OldnGrounded June 16, 2025, 01:19:00 GMT permalink Post: 11903028	Quote: Originally Posted by bbofh The TCMA patent application is at: https://patents.google.com/patent/US6704630B2/en Quite a simple system (not) What gets your attention is the fact that you can continue to operate the aircraft without an MMEL entry when one of the two systems (per EEC) that shadow each other... is unserviceable. As it says: "Typically the aircraft is allowed to operate for a limited period of time with just a single operative processing subsystem." That 787 was not long out of maintenance. Thanks for posting this. I read it quickly and glanced at the drawings, which are adequate for the patent application but not nearly adequate to understand the system in any depth. I note that, unless I missed it, the patent application doesn't address a mechanism for determining whether an aircraft is actually on the ground. I suppose that will depend on some of those "several other digital inputs." Quote: Via the execution of software package 130 , each of the processing subsystems 20 a and 20 b monitors the position of thrust lever 36 , engine power level, and several other digital inputs provided from the aircraft via digital ARINC data buses 46 . . Emphasis added. I'm still looking for identification of the relevant inputs for TCMA on the GEnx-1B. If anyone has suggestions, please share. Subjects (links are to this post in the relevant subject page so that this post can be seen in context): ARINC
OldnGrounded June 16, 2025, 01:33:00 GMT permalink Post: 11903033	Quote: Originally Posted by Keith. From six paragraphs down in the TCMA patent application. " The method of the present invention compares the engine's actual power level with a threshold contour defined by the TCMA software package. When the TCMA software package determines that a thrust control malfunction has occurred, based on the engine's power level exceeding the threshold contour, the engine is shut down by the TCMA circuit." Right. When the aircraft is on the ground. What inputs are used to determine whether the aircraft is on the ground? Subjects: None
OldnGrounded June 16, 2025, 01:40:00 GMT permalink Post: 11903037	Quote: Originally Posted by AndyJS This has just appeared in the Times (of London) which is usually one of the most reliable sources of information in the UK. "A loss of engine power is emerging as the most likely cause of the crash of the Air India Boeing that killed at least 279 people at Ahmedabad on Thursday. The Boeing 787-8 series appeared to have suffered from lower than normal thrust from its General Electric GEnx engines as it took off and failed to climb more than 450ft before crashing, video and reports from the Indian authorities have indicated.The new information has eclipsed an early focus on the unusual configuration of the aircraft\x92s wing flaps and landing gear." https://www.thetimes.com/world/asia/...rash-vhqw6b7v3 (subscription required to read the article) Thanks for the heads up. The story also says, "No cause has yet been identified for what would be an extremely rare power loss from both engines, but on Sunday the Indian civil air authority (DGCA) began urgent pre-flight inspections of fuel systems, electronic engine controls and other systems on Indian Boeing 787s." And it quotes Juan Browne (Blancolirio): \x93There was something terribly wrong with this 787 jet and we need to find out really quickly what went wrong because we\x92ve got a thousand of these operating today and operators need to find out what happened.\x94 Subjects (links are to this post in the relevant subject page so that this post can be seen in context): DGCA GEnx (ALL)
OldnGrounded June 16, 2025, 02:15:00 GMT permalink Post: 11903057	Folks, if an interim report or other official communication from the investigation is released, it will almost certainly come from India's AAIB or at least be posted to its site. So checking there before posting something like that here would be a really good idea. https://aaib.gov.in/ Admin note: the url is correct, app are the Government allow advertising on their sites! SPlot Subjects (links are to this post in the relevant subject page so that this post can be seen in context): AAIB (All)
OldnGrounded June 16, 2025, 03:41:00 GMT permalink Post: 11903083	Quote: Originally Posted by Pip_Pip Does the article say anything about the toilet habits of bears? Please, we really don't need any more snark in this thread. And your snark suggests that you may not understand the implications of the story cited in the posts you quoted. That the Times reports, clearly based on information from official Indian sources, that loss of thrust in both engines was a key factor in this crash, and that DGCA has ordered urgent inspections of 787s because of preliminary findings of the investigation, is important news from one of the most responsible newspapers anywhere. And Juan Browne's urging quick action and citing the importance to the entire fleet and to aviation generally is also significant. He's a respected aviator many here pay serious attention to. Subjects (links are to this post in the relevant subject page so that this post can be seen in context): DGCA
OldnGrounded June 16, 2025, 03:52:00 GMT permalink Post: 11903086	Quote: Originally Posted by fgrieu Among the most interesting of the Times article: I wish we had quotes of "the Indian authorities". Yes, so do I. But we live now in a world where information from officials who aren't quoted because they aren't authorized to speak, or are authorized but insist on anonymity, is very often the only information available, especially early in an investigation like this one. The fact that this story is in the Times gives me a fair amount of confidence that what is being reported really is from official sources. They actually have journalistic standards there. Subjects: None
OldnGrounded June 16, 2025, 02:15:00 GMT permalink Post: 11903737	Folks, if an interim report or other official communication from the investigation is released, it will almost certainly come from India's AAIB or at least be posted to its site. So checking there before posting something like that here would be a really good idea. https://aaib.gov.in/ Admin note: the url is correct, app are the Government allow advertising on their sites! SPlot Subjects (links are to this post in the relevant subject page so that this post can be seen in context): AAIB (All)
OldnGrounded June 16, 2025, 23:49:00 GMT permalink Post: 11903875	Quote: Originally Posted by Lead Balloon (I understand from the now-closed thread, that there is an unresolved question as to whether a petition for an exemption from the TCMA requirement had been successful.) Unless I've missed another one, the relevant petition was for a time limited exemption for TCMA for the GEnx-1B. It was granted. ~~See attached~~ . Nope. Uploads failing. See here: https://downloads.regulations.gov/FA...tachment_1.pdf https://downloads.regulations.gov/FA...tachment_1.pdf I haven't yet been successful in finding the details of the solution that would have brought TCMA for that engine into compliance by the 2018 deadline requested and granted. Subjects: None
OldnGrounded June 17, 2025, 02:42:00 GMT permalink Post: 11903927	Quote: Originally Posted by Lord Farringdon [. . .] In this regard we can recall several instances of double engine failure associated with bird strikes generally involving large birds or large flocks or both. But it seems we have discounted this theory very early in discussion. Why? Because we cant see any birds, or flocks of birds or engine flames/surges or puffs of smokes from the engines which would support this. Really? [. . .] Edit: I might add, they would have found remains on the runway if this did indeed happen. But we have heard anything from anybody? It seems pretty unlikely that a bird strike that took out both of those very big engines simultaneously would not have been fairly obvious in ways that nearby observers (e.g., the crew, ATC, airport personnel?) would have noticed. Possible, of course, but I don't think we've seen any evidence that points in that direction. Also, for what it's worth, the Times of London June 15 story " New clues point to engine failure for cause of Air India plane crash " cited here in the closed thread includes this: Quote: The Indian authorities indicated that a bird strike has been ruled out. A poster in the closed thread pointed out, properly I think, that the Times shouldn't be relied upon for presentation or interpretation of technical information. Like most general news organizations, their reporters and editors (mostly) just don't have the background to assess, filter and explain complex processes and technology. Unlike many, though, the Times can generally be relied upon to seek appropriate sources and report accurately what those sources say. I think it's very likely that Indian authorities have ruled out a bird strike, and I also think those authorities are competent to make that decision. Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Dual Engine Failure Engine Failure (All)
OldnGrounded June 17, 2025, 03:02:00 GMT permalink Post: 11903932	Quote: Originally Posted by Lead Balloon Back to the subject of the TCMA, in order for the four channels (A and B for engine 1 and A and B for engine 2) to be truly independent, there would have to be, for example, four, separate weight on wheels sensors and two, separate throttle position sensors per throttle. I would be extraordinarily surprised if that's what has been implemented, but will happily stand correct. And a sensor per channel per engine for actual thrust, and sensor inputs in addition to WoW switches to validate on-ground state (perhaps radio altimeters, as described by tdracer for some of the 74s, which I misread as 787s). I, too would be surprised \x97 stunned \x97 if all of that had been implemented. I really want to know what exactly was implemented, and when and in which specific airplanes/engines. What I expect, though, is that when we learn all of that, we'll decide that it really is exceedingly unlikely that TCMA shut down those engines in Ahmedabad the other day. But it sure looks like something did. Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Weight on Wheels
OldnGrounded June 17, 2025, 03:34:00 GMT permalink Post: 11903943	Quote: Originally Posted by dragon6172 There are eight air ground sensors. Two truck tilt sensors and two strut compression sensors on each main gear. Thanks. Do we know that these are monitored by TCMA for air/ground state and if so, do we know the logic used to make a determination based on those inputs? Alternatively, do you know where we should be looking for those answers? Subjects: None
OldnGrounded June 17, 2025, 04:05:00 GMT permalink Post: 11903952	Quote: Originally Posted by dragon6172 No idea. I only got that info from the Master MEL on the FAA website. According to the MMEL the aircraft can be dispatched as long as there is one of each type sensor working on each main gear. (AIs MEL could be more restrictive) Thanks again. Yes, I checked the MMEL too. ~~It also says that the aircraft may be dispatched with one of two TCMA functions operational~~ . Edit: dragon6172 has pointed out that the cited MMEL entry for TCMA applies to Rolls Royce engines, so not relevant here. Last edited by OldnGrounded; 17th June 2025 at 05:06 . Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FAA MEL
OldnGrounded June 17, 2025, 05:03:00 GMT permalink Post: 11903972	Quote: Originally Posted by dragon6172 Pretty sure that the (RR) after that TCMA entry means it is only applicable to Rolls Royce engines. I believe the accident aircraft had GE engines? Ah, you're right. Didn't notice. And the accident aircraft did have GE engines. Thanks. Subjects: None

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