Posts about: "TCMA (All)" [Posts: 279 Pages: 14]

Lead Balloon
2025-06-18T11:42:00
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Post: 11905167
Originally Posted by syseng68k
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.
Boeing's patent application says:
In this preferred embodiment, TCMA circuit 16 is included in an electronic engine control (EEC) 18 that is mounted on an aircraft engine.
My understanding is that "EEC" is Boeing for "FADEC".

But I have to reiterate, and as others have noted, that we don't know what actual TCMA systems, if any, were fitted where and how it was wired into the accident aircraft's engines, or whether the specific state of the TCMA systems, if any, were monitored by the flight recorders.
OldnGrounded
2025-06-18T11:54:00
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Post: 11905176
Originally Posted by Lead Balloon
Yet the (a?) patent application for the TCMA addition to the EEC was filed by Boeing.
Yes, and Boeing specifies at least some of the functionality required in the FADECs.

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Lead Balloon
2025-06-18T11:57:00
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Post: 11905178
Though in fairness to Boeing, as I think I and others may have noted before, rumour has it that the FAA mandate for TCMA functionality was met with strong resistance (and I can understand why).

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syseng68k
2025-06-18T11:58:00
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Post: 11905180
Lead Balloon:

The requirement for TCMA may have been specified by Boeing, but that doesn' t tell us who designed and built the solution in this case, though it must have been a collaborative effort between the two parties. Anyway, TCMA may be a red herring, since we still have not defined what, if any, other sources would have authority to issue an engine shutdown command

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OldnGrounded
2025-06-18T12:15:00
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Post: 11905190
Originally Posted by syseng68k
Lead Balloon:

The requirement for TCMA may have been specified by Boeing, but that doesn't tell us who designed and built the solution in this case, though it must have been a collaborative effort between the two parties.
Yes, but Lead Balloon's posts on this were in response to your post suggesting that "you can't blame Boeing" because the engines and FADECs were built by GE. The real-world question might be who can't blame Boeing? I think the answer is probably that everyone who thinks blaming Boeing is advantageous would at least try to do so. And specification and collaboration would likely be and adequate basis for trying.

Again, I'm not suggesting that TCMA is causal or contributing in this accident, and I understand that there are multiple reasons why that is unlikely even if the air/ground determination was erroneous. I just still want to know what the air/ground inputs and logic are, because there just aren't many things we know about so far that could cause what most believe was at least an important contributing factor.

Edit: As Lead Balloon points out, it was the FAA that required TCMA. The fact remains that Boeing patented at least one version of the function and specifies/collaborates in implementation with the engine manufacturers — more than enough participation for anyone seeking to blame Boeing for (purported) failures.

Last edited by OldnGrounded; 18th Jun 2025 at 13:02 . Reason: Clarification after noticing Lead Balloon's correction.

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Lead Balloon
2025-06-18T12:25:00
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Post: 11905198
Originally Posted by syseng68k
Lead Balloon:

The requirement for TCMA may have been specified by Boeing, but that doesn' t tell us who designed and built the solution in this case, though it must have been a collaborative effort between the two parties. Anyway, TCMA may be a red herring, since we still have not defined what, if any, other sources would have authority to issue an engine shutdown command
The "requirement" for TCMA was "specified" by the FAA. Manufacturers seeking certification of aeronautical products subject to the requirements then had no choice but to design and instal systems that met the FAA's certification requirements.

I'm pretty sure it's clear what "sources", other than TCMA systems if any, have "authority to issue an engine shutdown command", though it does depend on what you mean by "engine shutdown".

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syseng68k
2025-06-18T13:11:00
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Post: 11905233
Lead Balloon:



“The "requirement" for TCMA was "specified" by the FAA. Manufacturers seeking certification of aeronautical products subject to the requirements then had no choice but to design and instal systems that met the FAA's certification requirements”.

I think that has already been established upthread.


“I'm pretty sure it's clear what "sources", other than TCMA systems if any, have "authority to issue an engine shutdown command", though it does depend on what you mean by "engine shutdown".”

I don’t think that is clear at all. The shutdown hypothesis, if true, both engines, makes it likely that they were commanded to do so. While the discussion has centered around the TCMA subsystem, if other subsystems have the ability to do that, they need to be defined and looked at as well.

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mechpowi
2025-06-18T13:32:00
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Post: 11905254
Originally Posted by syseng68k
Lead Balloon:



\x93The "requirement" for TCMA was "specified" by the FAA. Manufacturers seeking certification of aeronautical products subject to the requirements then had no choice but to design and instal systems that met the FAA's certification requirements\x94.

I think that has already been established upthread.


\x93I'm pretty sure it's clear what "sources", other than TCMA systems if any, have "authority to issue an engine shutdown command", though it does depend on what you mean by "engine shutdown".\x94

I don\x92t think that is clear at all. The shutdown hypothesis, if true, both engines, makes it likely that they were commanded to do so. While the discussion has centered around the TCMA subsystem, if other subsystems have the ability to do that, they need to be defined and looked at as well.
There\x92s at least N2 overspeed protection that actually uses the same hardware as TCMA to stop the noise. There might exists crosstalk and inhibit for the N2 overspeed protection if the N2 overspeed protection has shut down the other engine. In fact it\x92s not confirmed that no such crosstalk exists in 787 TCMA system. It would complie with \x94no single fault should cause\x85\x94 certification requirements. Other than that I see no practical difference in the propability of TCMA and N2 overspeed protection to shut down both engine during take-off.
syseng68k
2025-06-18T13:54:00
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Post: 11905269
mechpowl:
Thanks for that. That begs the question, if there is overspead protection already, perhaps multiple channels and sensors, why is TCMA needed at all ?. Blanket overspeed protection already covers the underlying requirement, ie: prevention of overspeed, all cases. Seems to be adding complexity for no reason.
EDML
2025-06-18T14:02:00
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Post: 11905276
Originally Posted by mechpowi
There\x92s at least N2 overspeed protection that actually uses the same hardware as TCMA to stop the noise. There might exists crosstalk and inhibit for the N2 overspeed protection if the N2 overspeed protection has shut down the other engine. In fact it\x92s not confirmed that no such crosstalk exists in 787 TCMA system. It would complie with \x94no single fault should cause\x85\x94 certification requirements. Other than that I see no practical difference in the propability of TCMA and N2 overspeed protection to shut down both engine during take-off.
That is how it's done on the EC-135 helicopter (also FADEC controlled). One failed engine will disable the overspeed protection for the remaining engine. Of course a helicopter is a whole different story, though.
mechpowi
2025-06-18T14:10:00
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Post: 11905281
Originally Posted by syseng68k
mechpowl:
Thanks for that. That begs the question, if there is overspead protection already, perhaps multiple channels and sensors, why is TCMA needed at all ?. Blanket overspeed protection already covers the underlying requirement, ie: prevention of overspeed, all cases. Seems to be adding complexity for no reason.
TCMA is there to prevent higher than commanded thrust while on the ground in purpose to ascertain expected deceleration. N2 overspeed protection is a much older concept from the days before FADECs to prevent overspeeding engine disintegrsting and potentially causing lots of damage to the aircraft. In a GE engined 787 the N2 overpeed protection, while operating as designed, first try to lower the N2 and only if that fails it will shut down the engine.

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rigoschris
2025-06-18T18:25:00
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Post: 11905452
Originally Posted by EDLB
We have two donks individual fuel supply cut simultaneous in split seconds. There is no rudder activity visible for any thrust asymmetry during this timeframe. TCMA is implemented via the FADECs which are independent for each engine with their own power source from each engine. TCMA is designed to shut down its engine if its power lever is in retard position and the engine is still powering with too much thrust. In addition the airplanes ground sensors must indicate that it is on the ground. For each thrust leaver there are two independent position sensors. It is similar redundant designed as in modern car acceleration pedals. A dual redundancy in each thrust leaver. For TCMA to shut down two fuel supplies within split seconds we have to assume that 4 thrust leaver sensors malfunctioned and the ground sensing logic failed at the same time. The probability that this happens is nil (may be 1 in every 10exp15 hours) which would be about 10 times the age of our universe.
Unless there is a software error in the FADEC TCMA system which only came to light on this flight. But there seem to be nothing special on this flight until rotation. If there is a software error I expect, that we get false single engine shut downs first. And that would already made the news if it happened during rotation.
Actually, according to tdracer , each channel of the FADEC gets just one throttle resolver input, as the two resolvers are on separate wiring looms. So, the FADEC is using the dual channel feature to handle erroneous throttle position inputs. However, according to the patent at least, each channel can trigger TCMA and cut the fuel supply independently. So now we're down to only needing only one erroneous throttle signal per engine. Or one wrong interpretation of a signal, e.g. value clipping where you shouldn't (shortcircuit -> idle), some integer overflow etc.

So, from my understanding, if there is an issue with some of the throttle position sensors, the FADECs will detect a disagreement and keep the high thrust -> assume safe is "fly", whereas one of the TCMA channels might read or misinterpret throttle position close to idle. As the thrust doesn't decrease, at some point the upper bound of the falling TCMA thrust contour will be breached and the engine will be shut down.

Last edited by rigoschris; 18th Jun 2025 at 20:09 . Reason: Rephrase potential interplay of TCMA with rest of FADEC logic

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Lead Balloon
2025-06-18T22:55:00
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Post: 11905604
Originally Posted by JPI33600
Once again, a question for people who know: what happens if voltage is applied to CLOSED coil of HPSOV when OPEN coil was already energized (dual conflicting inputs)?
I assume you're asking this because of the odd 'link', identified by an earlier poster, in the schematic in Boeing's TCMA patent application? If so, I wouldn't take that schematic as being accurate. There's at least one (other?) error in the schematic: The numbering of the diode in TCMA compared with the text explanation.

A 'big hands / small maps' schematic in a patent application is not a version-controlled circuit diagram of the implemented system.

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bbofh
2025-06-19T01:30:00
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Post: 11905658
The 787-8 landing gear retraction is primarily hydraulic, using the center hydraulic system for the main operation. However, the alternate gear extension system utilizes a dedicated electric pump to pressurize fluid from the center hydraulic system for gear extension. Obviously due its size and weight and staged retraction, the effort required to raise and stow the gear greatly exceeds that required for extension.

The main gear retraction/extension is controlled by the center hydraulic system.

It is apparent that the hydraulics failed when the engines shut down after breaking the down-locks and leaving the Main Landing gear bogeys in the tilt position, ready for a next step internal stowage and door closure (that was now never to happen). It is therefore apparent that the dual engine failure and consequent automated RAT extension was precipitated by this gear selection or retraction cycle and thus likely to be either WoW micro-switch or 5G Radar altimeter-effect associated. Due to accumulator depletion, the electric pump load would have spiked to replenish it. This may have precipitated the dual engine shutdown due to an unfiltered electrical surge affecting the Ground/Air microswitches (or a local 5G transmission affecting the RADALT) and resetting the TCMA.

The RADALT? Another plausibility? Because of the furore over a spasticated frequency allocation by the US FCC, the US FAA had finally “bought in” and declared that individual nations and their airline operators were responsible for their own 5G frequency spectrum allocations and for taking essential steps to ensure mitigation of the interference effects upon aircraft automated landings and other critical systems caused by their own national approved 5G spectrum decisions. It was admittedly a situation calling for extensive modifications to (and shielding for) the three radar altimeters fitted for redundancy considerations to all modern airliners... for Category 3 ILS approach and landing in zero/zero visibility conditions. The RADALT also features in many air-ground sensing applications. (eg the 747-8).

This was an unusual FAA “passing of the buck” to manufacturers such as Honeywell etc. (to sort out with client operators). But then again, it was not the US FCC’s right to dictate the specific 5G frequencies internationally. These spectrum allocations now vary over the wide selection of 5G phones available (and also nationally). 5G Radar Altimeters constitute a part of the ground/Air sensing that changes the TCMA from ground mode (able to fuel-chop engines) to the air mode (inhibited from doing so)... Ground activation is acceptable ...where fuel chopping of uncommanded thrust can prevent runway sideways excursions or runway length overruns. The question now becomes: “Is it more (or less) safe having an automated fuel-chopping capability on BOTH your left and right, rather than leaving it to the pilot to react via his center console fuel cut-off switches... in the unlikely event of a runaway engine after landing (or during an abandoned take-off)?

5G Frequency Variations

The frequencies of 5G phones vary nationally based on the frequency bands allocated and used by different carriers in each country. In the United States, for example, carriers such as AT&T, Verizon, T-Mobile, and others use a combination of low-band, mid-band, and high-band 5G frequencies. Low-band 5G frequencies typically range from 600 MHz to 1 GHz, mid-band 5G frequencies range from 1.7 GHz to 2.5 GHz, and high-band 5G (mmWave) frequencies start at 24 GHz and go up to 40 GHz . These frequencies are allocated by regulatory bodies such as the Federal Communications Commission (FCC) and can vary between countries based on spectrum availability and regulatory decisions. In other countries, the specific frequency bands used for 5G may differ, leading to variations in the frequencies supported by 5G phones. Additionally, the deployment of 5G networks can also influence the frequencies used, with some countries focusing more on sub-6 GHz bands while others prioritize mmWave technology.

5G interference? It may be an avenue worth exploring?

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EXDAC
2025-06-19T02:31:00
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Post: 11905680
The issue with 5G was the potential for interference with some models of radio altimeter. I think we have been told that RA is used in 787 air/ground logic. We have also been told that air/ground state is used to enable TCMA.

I think it very unlikely that 5G interference was a contributing factor but I can see why someone would be interested in asking the question.

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OldnGrounded
2025-06-19T03:23:00
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Post: 11905696
Originally Posted by EXDAC
The issue with 5G was the potential for interference with some models of radio altimeter. I think we have been told that RA is used in 787 air/ground logic. We have also been told that air/ground state is used to enable TCMA.

I think it very unlikely that 5G interference was a contributing factor but I can see why someone would be interested in asking the question.
I think the cellphone interference concern is indeed partly focused on radio altimeters, and also on some voice comms. 5G shouldn't be problematic for the altimeters though. Modern ones operate at around 4.2-4.4 GHz, IIRC, and that's pretty far from any of the three bands 5G uses. I seem to remember reading that EASA tested for 5G interference and that it permits 5G use in the cabin. Whether that's true or not I don't know. And it wouldn't be easy, or even realistic, to police it in an airliner cabin.
FlightsofFancy
2025-06-19T04:23:00
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Post: 11905710
More holes in the Swiss Cheese?

Originally Posted by Machinbird
Early during the 787 flight testing phase (9 Nov 2010) before the battery fire escapades, there was an electrical fire aboard aircraft ZA002 that had potential for serious consequences.
From memory, the 787 electrical distribution does not involve electro-mechanical contactors but instead uses solid state devices that are controlled by software.
The Air India accident aircraft was experiencing electrical problems in the cabin on the prior flight according to passenger reports.
Were these problems addressed or where they non-MEL items?
The accident aircraft seems to have experienced a significant electrical event coincident with transition from Ground to Air mode (which I would expect results in some software reconfiguration of the aircraft electrical system).
If the ground to air transition momentarily activated a grounded electrical system, then there could be a rather large plasma cloud of vaporized metal surrounding adjacent wires which could send electrical power to places it would not normally go.
Swiss Cheese model anyone?
Very interesting. Pal of mine used to fly. Caught up with him last night over text. This is what he said:

\x93An aircraft can be in service for many years before supposedly 'random' failures are discovered. We had a 747-400 departing JNB many years ago, and during the take off roll, the inboard leading edge flaps (flaps on the Jumbo, not slats) retracted. The only indication of this was the flaps secondary display popping up and crosses appearing over the inboard LE flaps. No Master Caution, no warnings of any kind. Apparently the system was working exactly as 'designed\x92!

During the landing roll, when Reverse is selected, the inboard LE flaps automatically retract, to avoid damage from any debris blown up by the effect of the reverse thrust.

In this take off scenario, due to maintenance work being carried out earlier in the day, the aircraft thought the reversers had been selected, and 'correctly' retracted the flaps. At rotation, the stick shaker activated, and the aircraft struggled to get airborne. The passengers got lucky, as the First Officer, who was Pilot Handling, was an experienced aerobatic pilot, and was able to keep the aircraft airborne, flying in heavy buffet and with the stick shaker activated until the air-ground logic finally caught up after gear retraction, and the LE flaps deployed again.

Not something that most regular guys would cope with, particularly at night, with no outside horizon for reference. Pilots who\x92ve operated around Africa will know what I'm talking about.

They dumped fuel and returned to JNB.
This happened on May 11th 2009 (Google it) - just how long had the Jumbo, of all variants, been in service before this 'glitch' was discovered?

The actual issue was that during the earlier maintenance, the engineers had cycled the thrust levers, with the engines off, all the way through the reverse gates, and back again (the aircraft had arrived earlier that day, and a reverser had failed to deploy). What no one knew, was that the action of moving the thrust levers through the reverse gate, would latch a bit of software logic in one of the computers on board, causing a near catastrophic sequence of events.

We all know and love the Jim Reason Swiss cheese model - I suspect we're going to discover some previously unknown holes.\x94

I find it rather a coincidence that this aircraft had so many electrical problems, had, not been retrofitted to solve one electrical issues like all 787s in the US had, and suffered what appears to be some kind of electrical failure.

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retiredCSE
2025-06-19T13:48:00
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Post: 11906032
aborted RTO

I have read that TCMA can not activate unless TL set to idle . How about this made up scenario . During takeoff run close to takeoff speed PF decides to reject for ANY reason and moves TL-s to idle . PM (captain ? ). Says my airplane we are continuing and move TL-s back to full trust . TCMA triggers and shuts off the fuel . I am not implying that crew did anything wrong .
OldnGrounded
2025-06-19T13:51:00
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Post: 11906035
Originally Posted by bbofh
Has anybody the skill, knowledge, hands-on system familiarity or diagrammatic access to examine the
Ground/Air,
gear-handle,
gear doors
gear position lights
emergency extension,
Throttle lever position and
W.o.W. circuitry - in any sanguine detail?
I hope/wish. I accept that it's not at all likely that TCMA is the/a culprit in this crash, but it is, like the cutoff switches, one of the few things designed and intended to shut down an engine in a very big hurry. It would be good to know as much as possible about how it determines the aircraft's ground/air state.

And add the radio altimeter(s). I think, but don't know, that they provide inputs to the FADEC TCMA function also.


Last edited by T28B; 19th Jun 2025 at 14:38 . Reason: brackets completed

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OldnGrounded
2025-06-19T13:55:00
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Post: 11906038
Originally Posted by retiredCSE
I have read that TCMA can not activate unless TL set to idle.
I'm pretty sure that's not true. Everything I've found or read, and authoritative posts by tdracer, indicates that the required condition is thrust, as measured at N2 IIRC, higher than thrust lever position commands. The lever(doesn't) hsve to be at idle.

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