Posts about: "Engine Failure (All)" [Posts: 410 Pages: 21]

Yes. Thank you tdracer. All those postulating TCMA / FADEC faults please read and understand this clear explanation.

Then, ask yourselves which extraordinarily low probability bundle of previously unrevealed faults could spontaneously manifest themselves on both engines simultaneously.

Also ask yourselves why these faults manifested at that critical phase of flight and not during taxiing or take-off roll when some of the TCMA sensors would have been primed.

Yes. Thank you tdracer. All those postulating TCMA / FADEC faults please read and understand this clear explanation.

Then, ask yourselves which extraordinarily low probability bundle of previously unrevealed faults could spontaneously manifest themselves on both engines simultaneously.

Also ask yourselves why these faults manifested at that critical phase of flight and not during taxiing or take-off roll when some of the TCMA sensors would have been primed.

After reading tdracers informative post this morning, I too was musing: Why is all this attention being given to TCMA.

Of course, when the probable cause is profoundly unclear, our continuing distrust of latent technical systems comes to the fore .... as sadly, the shadow of MCAS still looms large in our imaginations

I was not aware that we have granular ADS-B data from the a/c itself showing airspeed post rotation (rather than speed interpolated from GPS). Apologies if I have missed it. If it does show acceleration after takeoff I tend to agree with you.

In no particular order, here are some more thoughts on TCMA having caught up on the thread:

If you cut the fuel from two big engines at take-off power, there must be some delay before n2 decays below the threshold for generation (below idle n2), the generators disconnect and RAT deploys. GEnx have relatively long spool up/down times as the fan is so large (and would be exposed to 170+kts of ram air). Perhaps someone has a view on how long this would be, but I imagine it could easily be 10s or more between fuel cut off and RAT deployment. On AI171 the RAT appears to be already deployed at the beginning of the bystander video. That starts c. 13s before impact and around 17s after rotation. This does not prove anything except that the supposed shut down must have happened very close to rotation and could have happened just before rotation while the a/c was on the ground.

As a thought experiment, imagine if ANA985 in 2019 had decided to go around. The a/c rotates and is ~50 ft above the runway, suddenly both engines spooling down, very little runway left to land on and no reverse thrust available. I am struck by how similar this scenario is to AI171. This theory would require there to have been unexpected thrust lever movement in the moments before rotation - but plausibly one pilot moving to reject, followed by an overrule or change of heart - or even a simple human error such as the recent BA incident at LGW - could achieve this. This is perhaps more likely that any sensor fault that you would expect to only impact a single engine given the redundancy of systems.

Tdracer writes that a key requirement of TCMA is to identify an engine runaway in the event of an RTO, in order to allow the a/c to stop on the runway. This will have been tested extensively - it is a big leap to imagine a false activation could be triggered. It did happen on ANA985 but through a very unusual set of inputs including application of reverse (albeit this latter point may not be relevant if TCMA logic does not distinguish between the reverser being deployed or not).

Incidentally there is an assumption the TCMA software version in place on the ANA flight had already been patched and fixed on AI171. That probably is the case but I am not sure it is a known fact.

In summary I remain baffled by this tragic accident. I have not yet read anything that explicitly rules out TCMA activation and it remains a possibility due to the vanishingly small number of factors that could shut down two engines at apparently the exact same moment when they have fully redundant systems. Fuel contamination, for example, has typically impacted each engine a few minutes (at least) apart. I am also cautious (as others have pointed out) of a form of confirmation bias about Boeing software systems with four-letter acronyms.

In my mind the cause could equally well be something completely different to anything suggested on this thread, that will only become clear with more evidence. All of the above also incorporates a number of theories, i.e. that there was an engine shutdown - that are not conclusively known.

Thank you to the mods for an excellent job.

My information differs to yours, We do know the EAFR was recovered on Saturday. Are you suggesting that it sat in a room for three days?

Wow you seriously think a professional crew would shutdown an engine below 400 feet?
​​​​​​​Is there any yaw or rudder deflection in any videos?

If you read the thread, you would know:

The RAT was almost certainly deployed. 4 different sources.
The Flaps were not retracted. Visible at the accident site plus many other sources agreeing they were indeed down.
APU will autostart when all engine power is lost. Potentially explaining why the inlet door was open or partially open at the accident site. Mentioned in several previous posts
On a 787-8, the main bogies tilt as the 1st action of the gear retract sequence. As stated in previous posts. I don't think this happens unless gear is selected up. So the conclusion was, gear was selected up. One caveat, IIRC, there was some discussion around a failure could have caused the bogies to tilt without Gear up being selected but I don't recall the outcome.
As for the Air France remark, un-necessary IMHO. Let's respect the crews please.

Not a pilot, but an engineer with some experience in accident / incident investigation.
One thing that strikes me in this and the previous closed threads is the lengthy back-and-forth discussion about potential technical faults that could lead to this accident.

However, there has been relatively little discussion about the #1 cause of all airplane accident - pilots' mistakes.

Except for the initial conversation about mistakenly retracting flaps instead of landing gear, which eventually was dismissed in favor of engine failure as there has been an almost unanimous agreement that even if such mistake was made, it was recoverable.

But what if the pilots made more than one consecutive mistakes?

Mis-diagnosing the first abnormal behavior and making things worse by performing another action that instead of correcting the first mistake, turned the situation unrecoverable. The history of aircraft accidents is full of examples when a first, relatively benign issue was made much worse and eventually tragic by pilots' subsequent actions.

Frankly, I think it is much more likely that the pilots made several consecutive mistakes than eventually led to the crash than a 1-in-a-billion unrecoverable mechanic failure. I'm looking forward to the CVR and FDR transcripts and I suspect that we will learn that after whatever happened first (pilot's mistake or minor technical failure), it was subsequent pilot's action that turned a manageable situation into a tragic accident.

I do not wish to speculate on the cause of this horrible accident but this vey situation happened to a good friend of mine, former Tornado pilot with 25 years on airliners, as a captain and PF on a B777. In his words he was initially totally confused why the aircraft stopped climbing. He engaged the autopilot and quickly realised the problem but they came very close to stalling.

I would not like to place money on how quickly I would recognise the, highly unusual, situation of flaps being retracted with the gear remaining down and react appropriately.

The Air India flight was circa 30 seconds from lift-off to crashing.

I am sure an initial report will soon publish the basic facts.

DIBO:

That was a partial answer, but still too many variables. Not nitpicking , but if you are trying to trace the source of a possible engine shutdown, you first need to list all the functions that have authority to do that, at source. Then generate a diagram showing all the steps along the path from those sources to the shutdown point. Truth is, we just don't have enough data to do that.

Thanks as always TDR for your excellent professional input. It is therefore so much more perplexing that even you cant logic our way out of this impasse. That is, the assumption that the aircraft experienced a double engine failure (supported by a reasonably convincing argument that the RAT deployed), and yet no plausible reason (that we can see) for such an event. So some then collectively slip into the tired and lazy theories of intentional or unintentional crew actions that 1. beggar belief (intentional), 2. defy physics (flaps instead of gear despite clear evidence to the contrary) and call into question the professionalism of a very experienced Captain and crew as well as the aircraft manufacturer (because...well its Boeing so it must be software ).

Yet, the answer must be simpler and staring us in the face since logic and experience (everything you have offered TDR), tell us that modern airliner engines generally do not just suddenly quit flying at the same time. 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?

I have read all the 100's of posts (sadly) and while some very early posters tried to analyze the imagery, I suspect the very poor quality eventually discouraged most from seeing anything of interest. However, smattered throughout this discussion from the beginning to the end there have about four posts that describe seeing something where others have not. At least two of these were related to possible smoke but which were probably just the dust blown outwards by the wingtip vortices. Two others however have mentioned possible flames and puffs of smoke.

The video of course is very poor. There should be a special place in hell for people who subject us to looking at a video with continuous zooming in and out, inability to retain focus on the subject (it was just a CCTV monitor, not the actual aircraft they had to focus on) and constant camera shake. A video of a video, and then the resolution probably reduced for social media upload. This all results in a very unwatchable record of the aircrafts departure. The only immediate information gleaned seems to be some idea of how far down the runway the aircraft was at takeoff and the parabolic curve as it very clearly described the aircrafts flight path.




Air India Flight 171 on departure
But take a look at this frame. The right engine shows an artifact (pixelation if you like) that might represent a surge flame. I can almost see a puff of smoke just inboard of the aileron that may be associated with that too.

Am I just seeing distortion? Am I just seeing some smoke because that's where I would expect to see it?
We are all very used to seeing everything in 4K today but back in the day when everything was low res we used to join the dots. If pixels existed then something was there. If they didn't, it wasn't.
So if it's just pixels caused by distortion then they have coincidentally appeared in the tailpipe of an aircraft that crashed shortly after takeoff with a presumed double engine failure.

But surely we would see the birds? Well, not in this video. You cant even see the registration number on the side of the aircraft and that is much bigger than a bird. Haze, distortion, focus and low res, and each individual bird wouldn't even make up a pixel.

So make of this what you will, but this problem may have started on the ground. Birds strikes are very common according to Some AI pilots who interviewed for this following article but I have no idea of the authenticity of this report:

https://www.rediff.com/news/report/a...h/20250613.htm "The Air India pilots also added that Ahmedabad airport has long been known for bird activity near the runway, which could have contributed to the incident.

"This issue (of the excessive presence of birds) has been flagged multiple times," a third Air India pilot said, asking not to be named."
Of course, a single engine failure would not have brought this aircraft down, nor would it have deployed the RAT, but we can't see what happened on the left engine when the aircraft slipped behind the radio antenna building.

While these high bypass engines are designed and certified to keep running after experiencing certain types of bird strike, the effect on two engines concerns have been voiced about the contribution of certification to the mitigation of the risk hazardous bird strike in the two engine case.

This from Sky Library:
https://skybrary.aero/articles/aircr...nue%20to%20fly .

" A number of concerns have been quite widely voiced about the contribution of certification to the mitigation of the risk of hazardous bird strikes:

• The case of bird ingestion into more than one engine at the same time is not addressed directly and it is clearly extremely difficult to meaningfully estimate the probability of such an occurrence. However, it has been observed that, since some of the current standards only require that a damaged engine can be safely shut down, this circumstance should be more fully considered when determining the acceptable outcome of ingestion into single engines, especially for the twin engine case.
• It has been noted that the potential effects of bird strikes on modern electronic flight control systems and flight deck instrument displays have not yet been fully assessed.

Maybe someone can do some video enhancing of this image as others have done with the audio enhancement to give strong probability of RAT deployment.

If my suggestion can be corroborated at all, then the question of what happened next becomes somewhat easier to answer. Perhaps neither engine stopped running but they did so with limited thrust? If anything from the pilots mayday call can believed, it wasn't engines shut down..it was no thrust. So why did the RAT deploy? Cant answer that. And, I cant imagine it would be manually deployed if both engines were still running.
However, TDR did say.

"On the 767 and 747-400, when you shutdown an engine and the IDG goes offline, there is a momentary 'glitch' in the electrical power system as it reconfigures for the available power source - this is why you see the flight deck displays flicker and return, and the cabin lights momentarily flicker."

Startle factor that electrically systems were about to fail? Manually deploy RAT?

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:

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.

WHEN something catastrophic happens, like dual engine failure, that then creates a query about any "duality" between two standalone systems that really should have nothing whatsoever in common... except the PF.
Nothing in common? Is that really the case for the 787-8 in the Air India 787 crash?
Look at these three TCMA-related links in the order presented and note the proforma prescriptive caveats in the first two:

https://downloads.regulations.gov/FA...tachment_1.pdf
https://downloads.regulations.gov/FA...tachment_1.pdf
https://patents.google.com/patent/US6704630B2/en

TCMA is designed to detect and accommodate single failures within the EEC/FADEC, preventing a failure from jeopardizing the safe operation of the aircraft.
Implementation:
It involves implementing specific software changes within the engine's control system (EEC).
Regulation:
After some incidents, the design change was mandated by regulators, with a deadline for production aircraft by December 31, 2018, and a retrofit plan for existing aircraft.
Boeing 787 Application:
The TCMA feature is specifically relevant to the 787-8 equipped with GEnx-1B engines, but it may also be applicable to other 787 variants using the same engine type.

The first two links are respectively the request for and FAA affirmation/approval for a GENx-1b software system called TCMA (Thrust Control Malfunction Accommodation). TCMA is the system that precludes High Uncommanded Thrust (HUT) after touchdown by fuel-chopping the engines. It is designed to avoid runway departures. One input is power-lever position. It's then fair to say that (additionally) Air/Ground sensing is quintessentially vital (as to when the system is "armed" and can do this fuel-chop). The third link is the complex description (with diagrams) of the patent application's design functionality of TCMA.
FROM THE 3rd link above:
"​​​​​​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." It is also notable that it says within the 3rd link that "Typically the aircraft is allowed to operate for a limited period of time with just a single operative processing subsystem."
That Air India 787 was not long out of maintenance.
We are then motivated to ask "what dictates the Air/Ground sensing". Is it just a Weight-on-Wheels microswitch or a RADAlt? (or both? or triplicated micro-switches?). We may then ask: "Did Air India implement the post-5G changes to their RADAlts that concentrated on maintaining their auto-land capability (in the face of 5G interference with RADAlts?) I seem to recall that the FAA's dictums on this pointed out that it was an individual nation's responsibility to both control their 5G frequency spectrums and implement changes to Radar altimeters that would work interference-free in critical phases of flight. What has the Indian regulator done in this regard as the responsible entity? The whole shemozzle, starting with the US Federal Communications Commission (FCC) spectrum allocations, was an ongoing fight between the telecom giants and their getting their new mobile tech to market.

So where are we going with this line of causal reasoning? The only commonality/duality between left and right engines is the software driving the TCMA as monitored by the TCMA software incorporated in each engine's EEC. Most pundits have identified the gear-tilt as evidence that only the centre electrically-driven pump can do the gear-tilt if the engines' other two hyd systems are suddenly both in QUIT mode (which accords also with the instant RAT deployment and loud noise heard by the sole survivor) - and an ensuing transition from climb-out to a deadly sinking and commensurate attitude change for speed maint.
My unavoidable conclusion is that the selection of gear UP and the breaking of the gear downlocks (and WOW sensing and energization of the RADALTs) called upon the TCMA to fuel-chop the engines (via the TCMA functionality in each engine's EEC).
We could start by looking at the No Break Power Transfer (NBPT) tech used in modern airliners. This has led to Gen Control Panel meltdowns in 777's due to GEN contact meltdown. I know of one instance when a 773 was reduced to a RAT only landing enroute and another where a disastrous MEC fire occurred after start on pushback at LHR. A description of the systems glitch often experienced is at the following link. It's quite apparently a "gear-up" hiccup with potential damning consequences for smooth TCMA operation. As to be seen in the quality videos, a fuel-chop provides no real clue (such as engine failure/smoke/fire classically does). An uncommanded "reset" of the two engine's TCMA's upon gear retraction (link below) is trackable to be the sought after "duality" leading to a "both simultaneously quit" engine failure. These momentary electrical glitches and instant "resets" are described in the two links below. Food for reasoned thought?

https://tinyurl.com/yn5ce4tz

https://tinyurl.com/3kkh6n3d

I'm honestly mystified by the obsession with TCMA. The FADECs control almost every aspect of the engines, so there must be numerous ways they could cause a failure or uncommanded shutdown. So, even if we assume that the engines failed due to faults in the FADECs, why assume that TCMA would be involved? Surely it's more logical to simply posit that some unspecified bug in the FADEC software caused the failure. That bug could be related to TCMA, but it could just as easily involve any one of the dozens of other subroutines that likely exist.

Various posters seem to assume that all it takes is an incorrect air/ground signal, and the engines would shut down. But in fact it would also require the FADECs to read the thrust levers as being at or near idle... AND the engines failing to respond to closure of the fuel metering valve. I've read the entirety of both threads, and I haven't seen anyone even attempt to explain how a malfunction within the airframe could cause both of those things to occur on both engines (or even one engine!).

There is at least one thing common to the TCMA on each engine: The TCMA software.

My recollection may be inaccurate, but wasn't there something in the software for 787 generator control units that would cause generator shut down if the aircraft was 'powered up' for a continuous 248 days? Same software, so all 4 generators would shut down. Is my recollection inaccurate?

What we do know, for sure, is that the TCMAs have the same 'authority' and effect as the fuel cut-off switches. The difference is that the crew control the latter.

Hardly surprising they have ruled out bird strikes.
Just take a look at the video of the Thomson 757 bird strike at Manchester, quite dramatic visual evidence from the affected engine, smoke and flames, none of which is observed in the IA accident video.

Agreed.
Also, I expect the airport would've sent a car out to check the runway for evidence. Since we agree that the engine failure occurred near rotation, and that rotation occured well inside the runway ( see e.g. fdr here , or the granular ADS-B data), that car would've encountered a bloody mess, and we'd all know about it by now.

The problem with these reports is that the Indian AAIB and DGCA websites ( aaib.gov.in www.dgca.gov.in ) are mute on the subject of this crash, so even the DGCA inspection mandate quoted above is shakily sourced. On Friday, AvHerald had already updated with "On Jun 13th 2025 the DGCA reported, that initial preliminary findings rule out a bird strike as no bird carcasses have been found." I searched for a source for this, and found an "exclusive" which read, "The initial probe report of the Ahmedabad Air India crash, accessed by CNN-News18, reveals key findings from the Directorate General of Civil Aviation\x92s assessment led by the director of security." Other media simply quoted News18. There are two reasons to be skeptical here:
\x95 first, we have seen fake reports circulating;
\x95 secondly, News18 rates badly on mediabiasfactcheck.com: "Launched in 2005, CNN-News18 (formerly CNN-IBN) is an English-language Indian news television channel based in India. We also rate them Questionable based on a poor fact-checking record with numerous false claims."
That leads me to consider that this "exclusive" might be sloppy reporting based on a fake\x97I have no way to know whether it is legitimate or not.

At this point, I feel we can only rely on information being official if it's published through an official website, or if there's independent reporting or a video clip from an official press briefing.

I do believe the accident was not caused by an animal strike, for many reasons.
But I wouldn't believe it based on unsourced reporting alone.

Perhaps?

• Takeoff proceeded normally, TOGA used.
  
• Autothrottle entered HOLD mode at 80 knots .
  
• VNAV or FLCH was NOT engaged after liftoff.
  
• Pilot assumed A/T was managing thrust, but it wasn’t.
  
• Pilot focused on pitch/flying manually.
  
• Thrust stayed fixed or decayed (if levers were moved).
  
• Speed decayed, aircraft climbed too steeply, energy bled off.
  
• Pilot assumed engine failure due to poor climb response.
  

Boeing SOPs typically include a callout at 400 ft like:

"LNAV" - "VNAV" or "FLCH SPD"

To ensure:

• Proper navigation mode is active
  
• Autothrottle resumes thrust management
  
• Aircraft transitions smoothly into the climb phase
  

There is a possibility that doesn\x92t get much air time on this forum that satisfies all the \x91facts\x92 ( pprune facts mind you), and requires less mental gymnastics to believe than many of the theories put forward. I\x92m not saying it\x92s what happened at all but it seems much more likely than a TCMA fault to me.
This link is to a Japanese report on a Jetstar 787-8 with GE engines that had both engines drop below idle while airborne due to magnesium salts effecting the operation of the FSV spools. The Magnesium salts came from a biocide dose by maintenance two days earlier.
For some reason I can\x92t paste the link but if you google JTSB the report number is AI2020-2.
I think it\x92s quite easy to imagine that a simple maintenance error ( 1000ppm instead of 100ppm) combined with extremely bad luck on timing lead to this accident.
I think I\x92m favouring a theory like this for its simplicity and the fact that fuel is the elephant in the room when you are dealing with a dual engine failure.

That’s really interesting, I’d not heard of that incident. The report does say though that particular biocide had been withdrawn due to other engine thrust occurences.

But would any of that trigger the RAT and/or cause the emergency lights to come on? (I know, there is only anecdotal evidence from the sole survivor of this).