IIRC, the TCMA is fitted to ALL 787s regardless of fitted power plant. A similar system, TCMP, may be found on (some) 777s.

Hope the descriptions below help.

TCMA (B787)Thrust Control Malfunction Accommodation

Thrust Control Malfunction Accommodation is an EEC function that provides protection against idle thrust asymmetry conditions while on the ground.

The EEC commands shutdown of the affected engine when the:

• airplane is on the ground, and
• thrust lever is at idle, and
• engine is above idle speed and not decelerating normally

The EICAS caution message ENG FAIL (L or R) is displayed with an aural beeper once the engine falls below idle speed.

TCMP (B777)
Thrust Control Malfunction Protection

The EEC provides protection against an uncontrolled high thrust malfunction during ground operation. The EEC shuts down the affected engine whe

• airplane is on ground,
• thrust lever is at idle, and
• engine is above idle speed and not decelerating normally.

The EICAS caution message ENG FAIL (L or R) is displayed when the engine falls below idle speed.
—

It's in that draft FCOM without a caveat to engine manufacturer.

Perhaps it's MELable on the RR but not GE?

Perhaps. Just seems odd to me. Thanks for the tip on the FCOM. I wordsearched "TCMA" in the FCOM earlier, but the acronym isn't used. Had to use different searchwords.

Thanks.

Thx for spotting my typo on FL, now corrected! This was posted on the closed thread 2, PM’d you the permalink.
regards

Yes, thanks, that helps.

Airborne use of reverse
 

2 Quotes:

I recall reading somewhere that one of the early jets (DC8?) could reverse two engines for descent control. (Herod)

The Trident could use reverse thrust for emergency descent, 10,000 ft/min, and before touchdown. The C17 can use reverse thrust on all engines for tactical descents at 15,000 ft/min. (Topgas)

On the DC8 it was permitted to use reverse in the air to increase RoD during a descent. This caused great discomfort due to vibration and was not encouraged. In the '70s, It also tempted an upgrading Captain on the DC-9, who had been a First Officer on the DC-8 to attempt airborne reverse thrust when on an overly steep approach to Malaga, although this was not certified on the -9. The result was loss of parts on one reverser, an emergency landing in MLG with unscheduled night stop - and failure of the upgrading.

Correct. Though I have no time flying the plane, I have dozens of hours in the DC-8-63 full sim of the airline I worked for at the time (Worldways Canada). I did many approaches in the center two engines in reverse. As there was no "back" [of the plane] I have no idea what it would have been like back there, but in left seat, it was no problem. I'm not aware that our pilots every did it in flight. I do know that a pilot once tried to back off the gate with reverse when there was no towbar available for pushback. One engine's buckets stuck in reverse and that was that for that flight. There was word that this was operationally very discouraged after that!

On the GEnx, the entire TCMA function is resident to the FADEC. It's possible to MEL dispatch with one FADEC channel inop - which effectively means only one channel of TCMA would be available. No need to have a separate MEL item.
I don't know enough about the Trent architecture to know why it needs a separate MEL item for one channel of TCMA failed.

Pardon my perhaps ignorant post, but based on what is known, as I read it....
TCMA CONSTANTLY monitors WoW and the thrust
At a possible RTO, with gear still on runway, the thrust would be closed?
Brakes on, a change of solution? Gotta avoid the overrun ?
Brakes off levers slammed full open ....
Does TCMA act too quickly.?






?
Quite

1) If the crew rejects the takeoff, and pulls the thrust lever to idle,
and then IF one of the engines does not spool down (fast enough),
TCMA will shut it off,
because an engine that's thrusting will not help with stopping,
and it might blow the aircraft sideways off the runway as the aircraft slows and rudder authority is lost.
So that is good!

2) But that did not happen, and the crew now wants to take off anyway (why....?).
PF pushes TO/GA or slams the throttle.
Now the engine is accelerating as commanded.
TCMA does not care about acceleration.

And should you be asking that in this thread? The incident here is a landing, not a take-off.
What may have happened here was
1) engines idle on glide,
2) touchdown, PF starts reversing
3) engines run up, PF undoes reverser and moves throttle to idle
4) maybe, maybe TCMA expects engine to decelerate faster from that than it does

So it's the exact opposite of a RTO, and because the throttle ends up on idle, TCMA can trigger. But on the RRTO, it ends up at full thrust, where TCMA won't trigger.

Thanks for responding.

Didn't mean to identify the other thread. Did I?

Because TCMA Constantly monitors thrust (N1), levers, and WOW, lag times become critical, yes? How long does TCMA wait, armed with instantaneous sensor input, to shut down engines ....?

It may seem that there are some questions ?? Timing is everything... Isn't an RTO at some point an emergency landing? Then if abandoned, a TO? Maybe put thrust reverse in there....?
,
Admittedly far fetched, ..... Impossible?

If there is any new information on the ANA event, discussion about that event here is appropriate. If that event has been thoroughly covered, let's let the general topic of 787 engine shutdowns pause for a little while... It is certain that a future topic will return discussion on this theme - patience......

Pilot DAR
One of the moderating team.

So, a fellow I don't know, infers from word on the street is that something is implicated, but can't quote directly, 'cause it's not verifiable!?!

I think a mod will delete that.... oh yeah...

Come on... We're professional aviation people! If we read that as a log entry, would we fly that plane?

There was something else in the deleted post's incorporated-by-reference blog post which seemed quite imprecise as well as suspect due to the nature of the omission. Although mentioning the NTSB's participation in the investigation, entirely missing from the blog post was any reference to the FAA - and the context was airworthiness of the type. Unless Annex 13 in effect rewrites the certification process (and I admit, not currently being posted to Montreal, maybe something changed but I missed it - kidding) the FAA, not the NTSB, handles major problems with airworthiness certifications.

Correct. The NTSB might tell the FAA that they have a concern, and perhaps make a recommendation, but it is the FAA (or equivalent national authority) who issues certification and handles airworthiness problems. I chose to not read the referenced blog post.

For those who do not know Dvid Learmount, ex pilot, long standing journalist with Flight Global, etc, see: https://www.airsafetymatters.co.uk/p...avid-learmount

The blog re Air India does refer to FADEC issues in an embedded link and the item on DGAC checks; but he does not pursue this aspect beyond -
There is a lot of credible information gathering that backs this up, but since its precise source is not certain, I will not run it here.
Meanwhile, be patient. This kind of accident is incredibly rare these days, and finding the truth behind it could not be more important.
https://davidlearmount.com

So, a couple of things: The PPRuNe rules (2&4) ask not to link to other aviation websites, just as a polite reminder to all. And, Remember, earlier up the threads we discussed not presenting information which really does not add anything of consequence to the discussion... We agree that posts which essentially say "listen to me, cause I have something to say", and there is not really a something there... are not desirable, 'just spins the hamsterwheel...

I read:

That's a hamsterwheel statement. Of course there's a lot of credible information... someone is reading flight data recorders! Its precise source is going to tell us when they're ready, 'cause they are not going to provide it faster because we're eager to hear. So it really doesn't add anything of value to state that you're not going to run it - 'cause yeah... there's nothing credible to run!

Kudos to one of our members, who is known to provide expert answers to the media on aviation events, who, for this event told the media that he would not offer an opinion yet . As was said, there are no points for being first here.

And, finally.... which thread is this one? Remember that this is not the thread for discussing the Air India accident...?

We mods really appreciate thought going into posts, which could be: "I got nothing to post, so I'll wait.".

Thanks, a member of your moderating team...

Hello everybody,
after reading the whole thread I wonder why it was impossible to start the engines again?! Even with the help from outside (technicians) it was not possible. Does the TCMA has this feature, not allowing to re-start the engines once activated?
Best regards

My first jet transport was the venerable B727. We went to work and MONITORED stuff. If an exceedance occurred or was likely, our monitoring led to actions to minimise damage. We also navigated from one aid to the next, and rarely got seriously lost. The ‘children of the magenta line’ also rarely get lost, but don’t necessarily monitor so much,and are not necessarily so flexible when, for instance, track shortening happens.

Sadly, the basics of the profession are being eroded to the point that we may be in danger of losing professional status. Don’t get me wrong, I loved some of the developments that gave us VNAV approaches and the like when prior it was a VOR or even NDB with dive and drive finales. That was/is a major improvement in safety terms. But, it comes with a cost.

That cost is complacency, and complacency kills.

With the introduction of auto induced shutdowns on start when exceedances are likely, and well documented and easily understood in the aircraft manuals we are quietly led to EXPECT that the aircraft will save itself. A quick reading of this thread indicates to me that there are still things that are either buried, or missing from the docs that we use to guide our daily work. I cannot for the life of me work out why an engine will EVER shutdown itself, except perhaps on start when the implications are ‘who cares’, because we are not even moving.

We all know that things break, failures occur. Why, for goodness sake, are we prepared to accept technical answers to problems that can be ameliorated by the unfashionable concept of active monitoring, and in doing so accept uncommanded (by flight crew) actions that impact on the operation during critical phase. I despair of what is happening to the profession and have no regrets that retirement called before all was lost. I feel that I am a dinosaur, however, some things were better in the not so distant past.

1) Because some failures happen too fast for crew to react; rotor burst due to engine overspeed being the classic example. And if you tell the crew that they must react and shut engines down in <2 seconds if they notice an anomaly, you'll have a huge number of false engine shutdowns, plus crews shutting down the wrong engine and... crashing.

2) Because a crew didn't shut down an engine that was stuck at maximum thrust, overran the runway, and wrote off the aircraft.

3) Because fuel, cost, performance, and weight savings can be achieved by running parts closer to limits, or making equipment faster-reacting (lighter) in such a way that the situation can change too fast for humans to monitor.

The inverse can be argued: if the automation can do the job equally or more reliably, why not automate it and let the crew focus on things that are more deserving of their attention?

I haven't been able to find this explained anywhere.

My guess is that it's some kind of lockout where the engine will refuse to start if it's on the ground and believes it's unsafe to do so, potentially implying a maintenance reset. If you tried to start an engine with a genuinely stuck open fuel valve, you might get a fireball or a sudden acceleration up to maximum thrust, knocking the aircraft off any chocks or parking brakes.

I understand and accept the points that someone somewhere makes. It would be interesting to to see the stats on why exceedences occur with FADEC controlled engines versus ‘steam driven’. I have from time to time pondered the Airbus ‘revolution’ of FBW. Is it possible that the’pilot proof’ aircraft simply meant that we crashed for different reasons,more related to misunderstanding or not being fully aware of the tech stuff (AFD sitems as an example) that is installed. As I said, I am a dinosaur, although not quite extinct. Please take my comments as meandering thoughts for discussion, rather than prescriptive ‘solutions’.

787 Operators NEVER power down their aircraft fully because powering it up again is a VERY long and painful process. When the crew walk away from an aircraft it is on gound power with the IRS and batteries turned off. If all engine generators unexpectedly dropped off line after landing you have a pretty dead aircraft that you might as well walk away from. The engineers will be busy for quite a while resuscitating it.

So this has been unclear to me. On TakeOff, with both in TOGA, say NUMBER TWO fails. Not yet at V1, PF retards both levers, number two because he/she knows it has Failed, and number one because he/she rejects the rotation ..


Assuming each engine is isolated from the other, Including TCMA, will both shut down independently, and "simultaneously"? Even though engine data is read as quite different? Asking if the airframe logic can suss the difference twixt legitimate
Dual shutdown and airborne dual shutdown?
Mode logic confusion... Thank you tdracer




If asked before, was the one second sample rate considered? Seems relying on steam sensors (WoW, levers discrepancy, etc) might conflict with instant FADECS??

If this is accurate, and TCMA " Does not care about acceleration, I see a problem.
Once WoW has triggered TCMA, once and done. No? Because I give TCMA. NO leeway. If it ShutDown thruston a landing, it's locked out, full stop. Eh?

Otherwise, the TCMA is piloting the aircraft...and TOGA should be right there, let alone the ability to relight...

First off, WoW, Lever angles, etc. are not "one second' - they are basically instantaneous. Thrust lever angle is read directly by the FADEC, at the FADEC 'minor frame' update rate (not sure about the Trent, the GEnx minor frame is 15 milliseconds). Once per second is the update rate for most parameters on the FDR - it's not the update rate the avionics use. I don't know specifics of the 787, but on the 747-8 the update rate for Wow and Radio Alt was about 10 times/second - I'd expect the ethernet based network on the 787 to be faster.

Let me say this again - TCMA will only take action if the engine is not responding normally to thrust lever movements. We use flight test data to validate the rates that we expect the engine to respond to lever movements, then add ~20% margin to that. So if you do an RTO because one engine failed, TCMA won't do anything on the good engine unless the engine stays at high power after the thrust lever is retarded. It's not related to the aircraft speed or acceleration rate - it's all to do with how the engine is reacting to what the thrust lever inputs are telling it to do.

Each FADEC sees the thrust lever for its engine retarded, and will thus send its engine to idle.
IF the N2 for the engine fails to go to idle, AND the aircraft is on the ground (and slow enough?), THEN clearly the FADEC has lost control of the engine (something broke), and TCMA will cut fuel to the engine. It'll be hard for the aircraft to brake if the engine thrust does not reduce, and likely depart the runway to the side, too, so the role of TCMA would be beneficial if the conditions for it to trigger are met.
If TCMA did not trigger, then the FADECs retarded the turbines to idle as commanded.
Nothing in this process requires the right and left side to communicate with each other.

If "Lighting your "Wingman" is not "Communicating", then I've got CPR all wrong...

Besides I am referring to a "Common Core" Consultation, not a party line.
We are discussing something that should NOT have happened...you don't get there by defending what was supposed to happen...

My point is that here, TCMA WAS ENGINEERED to prevent Overboost, or throttles incorrectly misaligned. Not to second guess the crew. Crew will bounce, it happens.
QF32 could have used a precautionary shut down on #2. ANA was doing just fine.
IMO,
Should TCMA BE Transferred to cover TOC? Leave landings alone?

TCMA?? Arse about? Should it be prohibited below 10k AGL?? Like sterile cockpit. I will tell you this rotor burst at altitude could have killed every body

Overboost on the roll also, but some will live, and after rotation it is supposed to mind its own business....supposed to...

No, TCMA was not engineered to do either of that.
When has TCMA ever second-guessed the crew?

I do not understand
* what you think happened,
* what you think should have happened,
* and how communication plays into this.

If you want any comments on this, you need to be explicit and detailed, and not talk in hints and riddles.

Your second part is correct. An unscheduled and unexpected loss of main bus power can take an age to put right.

The first part is wrong.
787s are powered down if they are not going anywhere for a while and servicing or maintenance is not required. It happens regularly.
Powering up a 787 takes longer than most legacy aircraft but it's not hours. Neither is it painful.
As long as you do it right.

I'm pretty sure you're BugBear under a different name, so I suggest you re-read and re-interpret this post again:

N2 Overspeed (and various equivalents) are designed to prevent a rotor burst by shutting the engine down if a particular rotor overspeeds. The Trent 900 on QF32 didn't have overspeed protection on its N2 rotor because it was thought that it was impossible for that rotor to overspeed without also overspeeding N3, which was protected. I expect that's fixed now.

Overboost is where the engine as a whole is running at too high a power setting, shortening engine life and risking failure. That's avoided by the control loops in the FADEC under normal conditions. If the FADEC thinks it's partially damaged and unable to properly determine some factors (usually sensor failures), the FADEC ends up in an alternate mode without overboost protection, which becomes the crew's problem. Overboost is a minutes problem, not a seconds or split-second problem.

TCMA shuts the engine down if it continues producing high thrust but the crew has that same engine set to/near idle. It only does this on the ground, because uncommanded high thrust in the air isn't a major hazard - there's always more sky above you, you can reduce thrust on the other engine to maintain altitude/drift down, and there's little time pressure.

TCMA doesn't care about throttle split. One engine operating and one engine stopped is a pretty big throttle split.

Rolls "TOS" system (Turbine Over Speed) is rather interesting - it checks for speed differences between the 'front' (compressor) and 'aft' (turbine) part of the shaft, and will shut the engine down if they differ (by more than some small tolerance). One issue with the 3 spool architecture is that bearing lubrication becomes tricky, and if the lube fails, the shaft can shear which can allow the turbine to accelerate rapidly to burst speed - faster than the normal fuel metering valve can react. This was first manifested on the RB211 - where an N1 shaft failure released the fan on an L1011 center engine - which then proceeded to try to cut the aircraft in half (fortunately it failed and they were able to land safely). This lead to the adoption of a 'fan catcher' - which worked to keep the fan pretty much in place, but then the unloaded turbine oversped and burst (happened at least once on a 747, fortunately without serious aircraft damage). This in turn lead to an N1 "TOS" - which could shutdown the engine (via the fuel control shutoff valve) in milliseconds. TOS was added to the N3 shaft when Rolls introduced the Trent series of engines, and then eventually to the N2 shaft after the QF32 event.
I don't recall now which shaft, but Rolls did an unplanned test of the TOS system on a Trent 1000 TEN engine when a shaft failed during an engineering test :eek: (it apparently worked as advertised).

BTW, GE uses a different design philosophy for a shaft failure - the turbine shaft is designed to move aft if the shaft fails, causing a clash with the fixed vanes in the turbine which slows the turbine preventing an overspeed (and the turbine case is designed to contain the resultant debris). There has been the odd shaft failure on GE engines over the years and none have resulted in a burst turbine - so apparently it works (granted, the CF6 series has had some burst turbines, but those were not the result of overspeed events).
No firsthand knowledge, but I believe the Pratt philosophy is similar to GE.

That would explain a lot...

"TCMA doesn't care about throttle split. One engine operating and one engine stopped is a pretty big throttle split."

Right. So if Reverse is selected, and both are producing thrust, Both are shutdown? If reverse is selected, and only one is making power, which one is cut? IOW, are there allowable conditions for TCMA to cut both, and not be relit? Cut one, and make it continuous OEI??? Is it possible for TCMA to cut the good engine?

TCMA only considers the one engine that the FADEC it is running on is attached to.
TCMA will only cut its engine when its throttle is at idle, but the engine won't go to idle.
If there's an engine "making power" when it should be idling, on the ground, don't you agree it should be cut?
Do you think that engine is a "good engine"?

Yes. If the plane bounces, it has not landed. In less than three seconds all four translating cowls could shut and Toga would be two seconds away. So, yes.... TCMA can NOT be programmed to frustrate or foul a feasible escape maneuver.
With respect, Leo
(During a landing, if a pilot initiates a go-around after having already deployed the thrust reversers, they must first manually stow the reverse levers before the TOGA switches can be effectively used or the forward thrust levers advanced.) GEnx. Do cascade reversers actually reverse thrust? Or, divert N1 sideways.

Cascade vanes are angled to direct the thrust forward. It's not completely in reverse but enough to be effective.

Hello Posters,

I have moved this thread here to the Tech Log, as it is an older event which has become an entirely technical discussion.

Pilot DAR

It's only “rollback and shutdown” if it comes from the Seattle region of Washington, otherwise it's just sparkling engine failure.

Vessbot
Not Engine Failure .....Extraneous software intrusion....

At BA, we normally didn’t power down between flights, however:

there was a problem discovered by Boeing, that if a 787 wasn’t powered down after a certain period of time (128 days?), there could be problems. So, the engineers had a schedule of “de-powering” each tail number on one of the occasions that it passed through LHR with sufficient turn-round time.

I had some status messages once at MEX which the engineers couldn’t clear, even though the originating fault had been fixed. After much head-scratching and liaison with London, the answer was to completely de-power the aircraft, leave it dark for 20 minutes, and then carefully power-up again.

Unfortunately, it was night, so all passengers had to be offloaded. Not normally a problem but we had 35 wheelchair users on board, so it took a while….

​​​​​​​But it worked!

• Airbus and Boeing both state that once thrust reversers have been selected, you are committed to landing. Failure of reversers to stow occurs, especially as reversers are usually locked out (stow or retract) while airborne. If you leave the ground with a reverser deployed, it will not stow until you return to the ground. So you are potentially trying to do a go around with one engine stuck in auto-idle with the doors open causing high drag.
  • Obviously some pilots break this rule.
  • https://www.smartcockpit.com/downloa...ision-to-stop/ (other source linked as Airbus Safety First seems to be down)
  • https://studylib.net/doc/26150546/th...irbus-safety-f... (other source linked as Airbus Safety First seems to be down)
  • https://www.faa.gov/lessons_learned/...cidents/C-FPWC
  • https://www.pprune.org/accidents-clo...eployment.html
  • This applies even to aircraft long predating TCMA, and I think is mostly due to the protections added after the Lauda 767 crash.
• The classic case for when TCMA would be critical is if you attempted to deploy or stow a reverser and the engine returned to full power uncommanded. You could then have one engine in full forward thrust and one engine in full reverse thrust. TCMA would activate to ensure that the engine is either a) doing what you ask it to, b) at idle because the reverser has failed, or c) shut down because the FADEC can't return the engine to idle.

See this video for an example of why you don't try to go around after reverse is selected. This is a 767, without TCMA. Once off the ground, the reversers cannot deploy or stow and are stuck where they are, with the engine stuck at auto-idle because the reversers are not in the commanded position.