2025-06-17T15:00:00
permalink Post: 11904376
The only thing I would add is the limited ADS-B data I have seen shows the a/c decelerating rapidly from the first data point onwards. It is possible the shutdown occurred when the a/c was on the ground (e.g. after V1). This may seem unlikely given the distance flown, but you can do the maths - a fast a/c has a lot of stored kinetic energy.
Last edited by lighttwin2; 18th Jun 2025 at 08:51 .
2025-06-17T15:09:00
permalink Post: 11904386
SLF. As usual feel free to ignore.
Being mere SLF, the knowledge that a mandatory system called TCMA even exists worries me a little. A system with authority to shut down (all) engines without any interference from one of the pilots should IMHO not exist in an airplane.
As described multiple times in the previous thread, TCMA uses data from multiple WoW sensors, ground radar and throttle imput. It is also described that TCMA will determine WoW status if ONE OR MORE of the WoW sensors senses WoW. Therefore it will only need one malfunctioning WoW sensor to determine WoW.
Since, as I read in the previous thread, it also uses ground radar: what is its hysteresis in measuring ground proximity? In other words from what height after rotation does TCMA deem the airplane is not at ground level anymore? This feels like an important parameter to me.
If, during this accident, something happened during its takeoff roll (unexpected throttle movement for instance), could that have triggered TCMA to shut down (both) engines?
I hope not.
By the way, what is the time delay between TCMA detecting an abnormality and it switching off an engine?
(If TCMA is somehow involved in this accident, a future change might be to disable TCMA after the airplane reaches a certain speed.)
Being mere SLF, the knowledge that a mandatory system called TCMA even exists worries me a little. A system with authority to shut down (all) engines without any interference from one of the pilots should IMHO not exist in an airplane.
As described multiple times in the previous thread, TCMA uses data from multiple WoW sensors, ground radar and throttle imput. It is also described that TCMA will determine WoW status if ONE OR MORE of the WoW sensors senses WoW. Therefore it will only need one malfunctioning WoW sensor to determine WoW.
Since, as I read in the previous thread, it also uses ground radar: what is its hysteresis in measuring ground proximity? In other words from what height after rotation does TCMA deem the airplane is not at ground level anymore? This feels like an important parameter to me.
If, during this accident, something happened during its takeoff roll (unexpected throttle movement for instance), could that have triggered TCMA to shut down (both) engines?
I hope not.
By the way, what is the time delay between TCMA detecting an abnormality and it switching off an engine?
(If TCMA is somehow involved in this accident, a future change might be to disable TCMA after the airplane reaches a certain speed.)
1 user liked this post.
2025-06-17T15:19:00
permalink Post: 11904392
1 user liked this post.
2025-06-17T16:41:00
permalink Post: 11904452
Question to avionics specialists again. Below is the main drawing of the TCMA subsystem, included in
the patent document
. I can't stop scratching my head about the link I have circled in
red
in the center of the image. AFAICS, this link shunts the internal RUN path of TCMA entirely : the RUN signal is supplied by the RUN contact of relay assembly 52, then goes through the common and RUN contacts of relay 22, then goes through the common and RUN contacts of relay 28, then exits TCMA subsystem 18 by wire 124, and... we're back to square 1, because of the link. So TCMA subsystem 18 doesn't actually control the OPEN relay 118 of the HPSOV, only the CLOSED relay 100, and in the case where relay 22 and/or 28 are activated, both coils of HPSOV could even be energized at the same time.
Obviously enough, this isn't a real circuit diagram, but shouldn't this link be removed from the patent drawing?
Odd link in TCMA patent drawing
Obviously enough, this isn't a real circuit diagram, but shouldn't this link be removed from the patent drawing?
Odd link in TCMA patent drawing
1 user liked this post.
2025-06-17T17:01:00
permalink Post: 11904468
B787 Skipper.... No longer able to sit on my hands!
The joker that published one or other of the fictional accident reports before the dead are even identified needs stringing up by the thumbs.... Well done mods. OK, some of these theories, just bearing in mind the the flight recorder (there is only one FDR + CVR combined) was in the intact section of the undamaged tail and has been with the authorities for almost five days......
- All you guys who are rushing down the TCMA rabbit hole: If it was established that a software error drove both engines to idle without warning, after rotate.... Don't you think the worldwide fleet of B787s would have been grounded by now? Such a glaring failure would be absolutely inescapable on the FDR.
Whatever was wrong with this aircraft was present at rotate, unbeknown to the crew. The fact that no ADs or notices to operators have been issued usually means that the cause is known and the aircraft was serviceable. The statement from a prominent Indian Captain about the skill and tenacity of the crew, right up to the last minute is absolutely laudable. However, the cynic in me says that the way is being paved for some bad news and by that I mean news that will do Air India reputational damage. Expect more management of expectation in the coming days.
I'm still going with
a) Incorrect derate + low Vspeeds or
b) Low altitude capture
The joker that published one or other of the fictional accident reports before the dead are even identified needs stringing up by the thumbs.... Well done mods. OK, some of these theories, just bearing in mind the the flight recorder (there is only one FDR + CVR combined) was in the intact section of the undamaged tail and has been with the authorities for almost five days......
- All you guys who are rushing down the TCMA rabbit hole: If it was established that a software error drove both engines to idle without warning, after rotate.... Don't you think the worldwide fleet of B787s would have been grounded by now? Such a glaring failure would be absolutely inescapable on the FDR.
Whatever was wrong with this aircraft was present at rotate, unbeknown to the crew. The fact that no ADs or notices to operators have been issued usually means that the cause is known and the aircraft was serviceable. The statement from a prominent Indian Captain about the skill and tenacity of the crew, right up to the last minute is absolutely laudable. However, the cynic in me says that the way is being paved for some bad news and by that I mean news that will do Air India reputational damage. Expect more management of expectation in the coming days.
I'm still going with
a) Incorrect derate + low Vspeeds or
b) Low altitude capture
11 users liked this post.
2025-06-17T17:09:00
permalink Post: 11904475
Question to avionics specialists again. Below is the main drawing of the TCMA subsystem, included in
the patent document
. I can't stop scratching my head about the link I have circled in
red
in the center of the image. AFAICS, this link shunts the internal RUN path of TCMA entirely : the RUN signal is supplied by the RUN contact of relay assembly 52, then goes through the common and RUN contacts of relay 22, then goes through the common and RUN contacts of relay 28, then exits TCMA subsystem 18 by wire 124, and... we're back to square 1, because of the link. So TCMA subsystem 18 doesn't actually control the OPEN relay 118 of the HPSOV, only the CLOSED relay 100, and in the case where relay 22 and/or 28 are activated, both coils of HPSOV could even be energized at the same time.
Obviously enough, this isn't a real circuit diagram, but shouldn't this link be removed from the patent drawing?
Odd link in TCMA patent drawing
Obviously enough, this isn't a real circuit diagram, but shouldn't this link be removed from the patent drawing?
Odd link in TCMA patent drawing
3 users liked this post.
2025-06-17T17:19:00
permalink Post: 11904487
B787 Skipper.... No longer able to sit on my hands!
The joker that published one or other of the fictional accident reports before the dead are even identified needs stringing up by the thumbs.... Well done mods. OK, some of these theories, just bearing in mind the the flight recorder (there is only one FDR + CVR combined) was in the intact section of the undamaged tail and has been with the authorities for almost five days......
- All you guys who are rushing down the TCMA rabbit hole: If it was established that a software error drove both engines to idle without warning, after rotate.... Don't you think the worldwide fleet of B787s would have been grounded by now? Such a glaring failure would be absolutely inescapable on the FDR.
Whatever was wrong with this aircraft was present at rotate, unbeknown to the crew. The fact that no ADs or notices to operators have been issued usually means that the cause is known and the aircraft was serviceable. The statement from a prominent Indian Captain about the skill and tenacity of the crew, right up to the last minute is absolutely laudable. However, the cynic in me says that the way is being paved for some bad news and by that I mean news that will do Air India reputational damage. Expect more management of expectation in the coming days.
I'm still going with
a) Incorrect derate + low Vspeeds or
b) Low altitude capture
The joker that published one or other of the fictional accident reports before the dead are even identified needs stringing up by the thumbs.... Well done mods. OK, some of these theories, just bearing in mind the the flight recorder (there is only one FDR + CVR combined) was in the intact section of the undamaged tail and has been with the authorities for almost five days......
- All you guys who are rushing down the TCMA rabbit hole: If it was established that a software error drove both engines to idle without warning, after rotate.... Don't you think the worldwide fleet of B787s would have been grounded by now? Such a glaring failure would be absolutely inescapable on the FDR.
Whatever was wrong with this aircraft was present at rotate, unbeknown to the crew. The fact that no ADs or notices to operators have been issued usually means that the cause is known and the aircraft was serviceable. The statement from a prominent Indian Captain about the skill and tenacity of the crew, right up to the last minute is absolutely laudable. However, the cynic in me says that the way is being paved for some bad news and by that I mean news that will do Air India reputational damage. Expect more management of expectation in the coming days.
I'm still going with
a) Incorrect derate + low Vspeeds or
b) Low altitude capture
Speaking as a B787 Captain..... There is so much rubbish and stupid suggestion being written here.
- RAT out? Almost impossible, I have seen no quality footage that definitively witnesses the RAT being out. Those who think they car hear a RAT type noise might be listening to a motorcycle passing or similar. It takes a triple hydraulic failure or a double engine failure to trigger RAT deploment. They happily went through V1 without a hint of rejected take off so as they rotated the aircraft was serviceable. These are big engines, they take a long time to wind down when you shut them down. I have never tried it however engine failure detection takes 30s or for the aircraft to react and they were not even airborne that long.
- RAT out? Almost impossible, I have seen no quality footage that definitively witnesses the RAT being out. Those who think they car hear a RAT type noise might be listening to a motorcycle passing or similar. It takes a triple hydraulic failure or a double engine failure to trigger RAT deploment. They happily went through V1 without a hint of rejected take off so as they rotated the aircraft was serviceable. These are big engines, they take a long time to wind down when you shut them down. I have never tried it however engine failure detection takes 30s or for the aircraft to react and they were not even airborne that long.
7 users liked this post.
2025-06-17T17:25:00
permalink Post: 11904491
Low Alt Capture
B787 Skipper.... No longer able to sit on my hands!
The joker that published one or other of the fictional accident reports before the dead are even identified needs stringing up by the thumbs.... Well done mods. OK, some of these theories, just bearing in mind the the flight recorder (there is only one FDR + CVR combined) was in the intact section of the undamaged tail and has been with the authorities for almost five days......
- All you guys who are rushing down the TCMA rabbit hole: If it was established that a software error drove both engines to idle without warning, after rotate.... Don't you think the worldwide fleet of B787s would have been grounded by now? Such a glaring failure would be absolutely inescapable on the FDR.
Whatever was wrong with this aircraft was present at rotate, unbeknown to the crew. The fact that no ADs or notices to operators have been issued usually means that the cause is known and the aircraft was serviceable. The statement from a prominent Indian Captain about the skill and tenacity of the crew, right up to the last minute is absolutely laudable. However, the cynic in me says that the way is being paved for some bad news and by that I mean news that will do Air India reputational damage. Expect more management of expectation in the coming days.
I'm still going with
a) Incorrect derate + low Vspeeds or
b) Low altitude capture
The joker that published one or other of the fictional accident reports before the dead are even identified needs stringing up by the thumbs.... Well done mods. OK, some of these theories, just bearing in mind the the flight recorder (there is only one FDR + CVR combined) was in the intact section of the undamaged tail and has been with the authorities for almost five days......
- All you guys who are rushing down the TCMA rabbit hole: If it was established that a software error drove both engines to idle without warning, after rotate.... Don't you think the worldwide fleet of B787s would have been grounded by now? Such a glaring failure would be absolutely inescapable on the FDR.
Whatever was wrong with this aircraft was present at rotate, unbeknown to the crew. The fact that no ADs or notices to operators have been issued usually means that the cause is known and the aircraft was serviceable. The statement from a prominent Indian Captain about the skill and tenacity of the crew, right up to the last minute is absolutely laudable. However, the cynic in me says that the way is being paved for some bad news and by that I mean news that will do Air India reputational damage. Expect more management of expectation in the coming days.
I'm still going with
a) Incorrect derate + low Vspeeds or
b) Low altitude capture
b) Wouldn\x92t it capture the Alt rather than descending thru it?
3 users liked this post.
2025-06-17T17:35:00
permalink Post: 11904503
<snip>
- All you guys who are rushing down the TCMA rabbit hole: If it was established that a software error drove both engines to idle without warning, after rotate.... Don't you think the worldwide fleet of B787s would have been grounded by now? Such a glaring failure would be absolutely inescapable on the FDR.
<snip>
- All you guys who are rushing down the TCMA rabbit hole: If it was established that a software error drove both engines to idle without warning, after rotate.... Don't you think the worldwide fleet of B787s would have been grounded by now? Such a glaring failure would be absolutely inescapable on the FDR.
<snip>
5 users liked this post.
2025-06-17T17:38:00
permalink Post: 11904506
B787 Skipper.... No longer able to sit on my hands!
The joker that published one or other of the fictional accident reports before the dead are even identified needs stringing up by the thumbs.... Well done mods. OK, some of these theories, just bearing in mind the the flight recorder (there is only one FDR + CVR combined) was in the intact section of the undamaged tail and has been with the authorities for almost five days......
- All you guys who are rushing down the TCMA rabbit hole: If it was established that a software error drove both engines to idle without warning, after rotate.... Don't you think the worldwide fleet of B787s would have been grounded by now? Such a glaring failure would be absolutely inescapable on the FDR.
Whatever was wrong with this aircraft was present at rotate, unbeknown to the crew. The fact that no ADs or notices to operators have been issued usually means that the cause is known and the aircraft was serviceable. The statement from a prominent Indian Captain about the skill and tenacity of the crew, right up to the last minute is absolutely laudable. However, the cynic in me says that the way is being paved for some bad news and by that I mean news that will do Air India reputational damage. Expect more management of expectation in the coming days.
I'm still going with
a) Incorrect derate + low Vspeeds or
b) Low altitude capture
The joker that published one or other of the fictional accident reports before the dead are even identified needs stringing up by the thumbs.... Well done mods. OK, some of these theories, just bearing in mind the the flight recorder (there is only one FDR + CVR combined) was in the intact section of the undamaged tail and has been with the authorities for almost five days......
- All you guys who are rushing down the TCMA rabbit hole: If it was established that a software error drove both engines to idle without warning, after rotate.... Don't you think the worldwide fleet of B787s would have been grounded by now? Such a glaring failure would be absolutely inescapable on the FDR.
Whatever was wrong with this aircraft was present at rotate, unbeknown to the crew. The fact that no ADs or notices to operators have been issued usually means that the cause is known and the aircraft was serviceable. The statement from a prominent Indian Captain about the skill and tenacity of the crew, right up to the last minute is absolutely laudable. However, the cynic in me says that the way is being paved for some bad news and by that I mean news that will do Air India reputational damage. Expect more management of expectation in the coming days.
I'm still going with
a) Incorrect derate + low Vspeeds or
b) Low altitude capture
Given they took off at a perfectly normal point, at a perfectly normal speed, I don't see how you come to incorrect derate and low v speeds, or how on earth that would lead to a normal takeoff followed by sinking?
8 users liked this post.
2025-06-17T19:58:00
permalink Post: 11904604
A question has crossed my mind today that may or may not have any relevance to the accident and for which I have not found an answer on here.
TCMA has been discussed here for a while, it will in a nutshell shut down an uncontrollable engine on the ground. Is there any additional lockout triggered if one of the installed engines is already not running, be it due to a TCMA emergency shutdown or due to some other reason? Or does TCMA have the authority to shut down any engine, whatever the operating state of the other engines may be, as long as the condition "not flying" is satisfied?
TCMA has been discussed here for a while, it will in a nutshell shut down an uncontrollable engine on the ground. Is there any additional lockout triggered if one of the installed engines is already not running, be it due to a TCMA emergency shutdown or due to some other reason? Or does TCMA have the authority to shut down any engine, whatever the operating state of the other engines may be, as long as the condition "not flying" is satisfied?
2 users liked this post.
2025-06-17T20:35:00
permalink Post: 11904634
Last edited by Lonewolf_50; 17th Jun 2025 at 21:17 .
2025-06-17T21:38:00
permalink Post: 11904692
Lonewolf_50,
thank You for the response. I admit to a little (possibly over-)simplification.
Having read the brief explanation by the man himself here , I note that that system appears strongly protected against inflight activation, but there is no word on a lockout in case it has been triggered on one engine already.
My thought comes from remembering the DH8, in which the autofeather system (that by another mechanism and due to different reasons than TCMA removes an engines capability to provide thrust and therefore appears to me slightly comparable in this aspect) had a system that ensured that once one propeller had been autofeathered, the system was disabled and did not attack the other engine. The risk caused by an inadvertent forced feathering of the other propeller was obviously deemed high enough to warrant such a safety latch.
Of course, TCMA is intended for ground operation only and has been quoted to be strongly safeguarded against triggering in flight. But still, from my laymans point of view, I was asking myself whether ensuring that TCMA will never kill both engines would be worthwhile, if only as a final barrier in case the system was mistakenly activated inflight.
thank You for the response. I admit to a little (possibly over-)simplification.
Having read the brief explanation by the man himself here , I note that that system appears strongly protected against inflight activation, but there is no word on a lockout in case it has been triggered on one engine already.
My thought comes from remembering the DH8, in which the autofeather system (that by another mechanism and due to different reasons than TCMA removes an engines capability to provide thrust and therefore appears to me slightly comparable in this aspect) had a system that ensured that once one propeller had been autofeathered, the system was disabled and did not attack the other engine. The risk caused by an inadvertent forced feathering of the other propeller was obviously deemed high enough to warrant such a safety latch.
Of course, TCMA is intended for ground operation only and has been quoted to be strongly safeguarded against triggering in flight. But still, from my laymans point of view, I was asking myself whether ensuring that TCMA will never kill both engines would be worthwhile, if only as a final barrier in case the system was mistakenly activated inflight.
2025-06-17T22:43:00
permalink Post: 11904732
That is not what the TCMA logic is supposed to do. Only high thrust with the thrust lever idle should trigger the TCMA.
2025-06-17T23:03:00
permalink Post: 11904743
BR, D Bru
2025-06-17T23:16:00
permalink Post: 11904752
Still FLS with some decent engineering background,
Said so my apologies if is not pertinent to the discussion.
I am puzzled by the TCMA logic, as shown on the patent, which of course could have nothing to do with final design, but clearly in my understanding the two FADEC channels are acting in series, therefore by design they do not need to concur to shut down the engine. Am I wrong?
Said so my apologies if is not pertinent to the discussion.
I am puzzled by the TCMA logic, as shown on the patent, which of course could have nothing to do with final design, but clearly in my understanding the two FADEC channels are acting in series, therefore by design they do not need to concur to shut down the engine. Am I wrong?
2025-06-17T23:20:00
permalink Post: 11904756
BTW, I don't know if there is any 'crosstalk' of TCMA activation between engines on the 787. I know we don't do any crosstalk of other engines info on the 747-8, but the 787 is far more integrated, and the amount of data that can put on that ethernet based data bus is massive.
My knee jerk is that they wouldn't crosstalk TCMA status between engines, but the reality is I really don't know.
8 users liked this post.
2025-06-18T04:11:00
permalink Post: 11904879
Still FLS with some decent engineering background,
Said so my apologies if is not pertinent to the discussion.
I am puzzled by the TCMA logic, as shown on the patent, which of course could have nothing to do with final design, but clearly in my understanding the two FADEC channels are acting in series, therefore by design they do not need to concur to shut down the engine. Am I wrong?
Said so my apologies if is not pertinent to the discussion.
I am puzzled by the TCMA logic, as shown on the patent, which of course could have nothing to do with final design, but clearly in my understanding the two FADEC channels are acting in series, therefore by design they do not need to concur to shut down the engine. Am I wrong?
In the words of the patent application: Both channels are \x93always actively monitoring engine function and independently have the capability of shutting down the engine.\x94
1 user liked this post.
2025-06-18T10:52:00
permalink Post: 11905135
To be fair, if the fault is shown to be from the FADEC, then you can hardly blame Boeing, since both engines and FADEC come from GE.The FADEC presents a command set and interface to whatever controls it, so a possible failure mode could be at that interface, a mismatch and or race condition between the controlling sequence of commands, and the FADEC response to that.
I guess we'll eventually find out what bits were actually connected to the engines fitted to the accident aircraft, by whom and when.
1 user liked this post.
2025-06-18T11:12:00
permalink Post: 11905152
Lead Balloon: "Yet the (a?) patent application for the TCMA addition to the EEC was filed by Boeing."
That sounds right, since it's an airframe related issue, not specific to the engine.
Your other implied question, ie: Is the TCMA software part of the FADEC , or something Boeing designed and built. Or, where is that functionality resident in the system, and who designed and built it ?. Starting to think that this tragedy may have had a far more subtle cause than has been imagined thus far.
That sounds right, since it's an airframe related issue, not specific to the engine.
Your other implied question, ie: Is the TCMA software part of the FADEC , or something Boeing designed and built. Or, where is that functionality resident in the system, and who designed and built it ?. Starting to think that this tragedy may have had a far more subtle cause than has been imagined thus far.