Posts by user "MaybeItIs" [Posts: 29 Total up-votes: 31 Pages: 2]

MaybeItIs
2025-06-13T09:12:00
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Post: 11900225
Originally Posted by Tech Guy
True. But possibly the pilot realised the gravity of their situation and decided that one last message of "what's happening" may help any following investigation.
Totally agree. I see an experienced and competent pilot who recognised that his luck has run out, but still did his level best to minimise harm and warn the authorities while he still could. I believe he was attempting to stall the plane as gently could into the ground as his last, best option.

Last edited by MaybeItIs; 13th Jun 2025 at 11:29 . Reason: spelling!

Subjects: None

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MaybeItIs
2025-06-14T12:00:00
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Post: 11901407
I haven't managed to read every post in this thread, just a large percentage, so please excuse me if these points have already been raised. I'll post each separately in case the mods deem them irrelevant or redundant, in which case, my humble apologies.

First, the RAT. There has been a lot of discussion about this, and I suspect the audio analysis a few posts above pretty well confirms that the RAT was deployed. However, I don't think the following question has been asked, and I believe it's further weight in support of RAT deployment.

Q: Why does the video of the plane passing at low altitude, (potentially taken from an apartment window or balcony door), even exist?

I have lived near an airport flight path for many years, and would never bother to video a passing plane unless I perceived it was truly exceptional. Normally, I don't even look, unless it sounds off course, very loud or some such reason. I have yet to take such a video. Here, of course, I'm assuming that the video-taker lived in or near the building concerned, and was therefore equally used to the sounds of passing planes. I submit that the video was shot purely because the camera man (by the voice sound, but an assumption - maybe not the camera operator's) recognised that the sound he was hearing was indeed exceptional. The video begins with the plane out of the shot, so he 'must' (assumption) have heard it coming, and had time to get his phone and starting videoing. Of course I'm saying that he was hearing the RAT...

Secondly, I have found that different versions of the same video play differently (on the same hardware). In some, I cannot discern the RAT sound - unless I reduce the playback speed. Then, it seems to be very distinct - but whether this is an artifact of the reduced playback speed, I can't say. I suspect that different playback applications and hardware will also have a major influence on the RAT audibility. I am 100% convinced that the RAT sound was captured, but is not audible to all, for one or more of these reasons.

Oh, lastly, I'm guessing the (AI) RAT frequency in the audio spectrum analysis was probably lower because the plane was travelling slower than in the other, more controlled cases. Equally, the load on the AI RAT could have been greater, for any number of reasons.

Subjects: Audio Analysis  RAT (All)  RAT (Deployment)  RAT (Sound)

MaybeItIs
2025-06-14T12:04:00
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Post: 11901413
My next question, again I believe not discussed, is what do the 787 Fuel Cutoff switches actually do? Obviously, they cut off the fuel supplies to the engines - pretty important in engine fire and other scenarios, but goes without saying. The real question is, what do they activate (or deactivate)? I'm assuming a simple solenoid valve, which is open when powered and closed when unpowered, but of course, there will (certainly) be Electro-Mechanical or Solid-State (Electronic) relays between the switches and the (solenoid valves).

I guess the next obvious question is, is there anything else that can turn off those Fuel Cutoff Valves - a computer condition for example. I'm assuming not, but I think it needs to be considered.

Taking each switch individually, next, since this is part of an electrical circuit, and of necessity must include Electrical Relays, there is certainly at least one and in all probability two electric Power Sources involved in this circuit. One supply which passes through the switch to activate the relay, and, I'm assuming, a second, higher current and probably higher voltage supply which drives the (solenoid?) valve.

As I see it, interrupting either supply will have the same effect - if the system is wired in the Positive-Postive sense, meaning a current through the switch causes the relay to pass a current through the (solenoid). If either of these supplies is cut, the Fuel Shutoffs will shut off the fuel. So, the question is, where do these supplies come from, and under what circumstances could they be cut off?

Sure, it looks to some (myself included) like a near simultaneous cutoff of both engines, but that doesn't have to have been caused by either of the pilots. I know there is huge redundancy built into the 787 Electrical Systems, but some of the evidence is suggesting that there was something not right with the plane's electrical system. I'm also fairly sure that there will be parts and places where certain faults can take the system down, despite the redundancy. I can't say where, but it's very difficult to design a perfect system, especially where there has to be transfers between multiple potential supplies and single actuators, motors or valves.

Having spent years repairing electrical and electronic systems, I know that the most difficult of all electrical faults are the intermittent ones. And I suspect that this is at the root of this crash. An intermittent or faulty AOA sensor has "caused" (provoked) multiple famous crashes... Can't find the one I'm looking for (pre-1980, I think) as the Max AOA issues dominate.

I can cite a very personal example, which involved the electrical supply to my house. I had several computers running 24x365 so of course, ran them off a UPS, which turned out to be a very good thing. I started to notice that at certain times, the UPS would activate - it would cut in and take over the computer loads, its alarm would go off to indicate a power fault. But the power was still on! This carried on for weeks and I initially blamed the UPS. Then, I noticed that it only happened on very hot afternoons... Long story short, the fault was caused by an electrical linesman, probably 30 years earlier, failing to tighten up a joint clamp on the phase wire to our house, across the street. Heating caused expansion then movement, and the power would momentarily go off then back on, and the UPS detected this. I note that this crash was on a hot day, and maybe this plane (which I believe was repositioned for the flight), had not been operating in such high temperatures recently, meaning the problem went unnoticed.


Subjects: Fuel (All)  Fuel Cut Off Switches  Fuel Cutoff

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MaybeItIs
2025-06-14T12:22:00
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Post: 11901429
What evidence do we have that the RAT was deployed? All I can find is people talking about a "noise" which seems very thin evidence indeed.
The existence of the video taken from a building near the flight path adds a lot of weight, to me.

Think about living next to a flight path. I do. I never take videos of passing planes. I doubt this video-taker did either.

But something incited him to pick up his phone (I guess) and start videoing, even before he could see the plane, which is out of view at the start. I suggest that he heard the RAT coming, knew it was totally out of the ordinary and thought it worth filming.

Why else would you film just another passing plane?

Also, looking at that video, I can see a "shadow" where the RAT would be. The RAT is very small compared with the landing gear, but there's something there. Largely lost to video compression, but it adds up.

And I can hear it, but not on every copy of that video. Try slowing the video down, but I don't know if that's reliable.

Subjects: Gear Retraction  RAT (All)  RAT (Deployment)

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MaybeItIs
2025-06-14T13:07:00
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Post: 11901468
This crash reminds me of the crash of a 747 Military Transport plane at an airbase in Afghanistan.

Shortly after TO, the cargo shifted, the plane became very tail heavy and stalled a few hundred feet in the air. It was the weirdest sight. For what seems a few seconds, the plane just seemed to hang there, presumably on engine thrust.

In this crash, the problem also seems to occur soon after rotation, as if something inside moved in response to its change in attitude. Maybe a loose connection on a main bus cable that moved... Maybe only a millimetre. Or a tool left inside an electrical cabinet slid somewhere it shouldn't. The possibilities are numerous, and without a lot more information, there's no way to know what caused this. I suspect a major electrical fault, probably intermittent.

How long would it take to restart those engines after a Fuel Cutoff flame out? Is that what happened, just before impact?

Subjects: Electrical Failure  Fuel (All)  Fuel Cutoff

MaybeItIs
2025-06-14T21:40:00
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Post: 11901866
Originally Posted by Icarus2001
That is because the take off roll and initial climb looks normal. Things go pear shaped at about the time the gear should be retracting.
Thanks for answering the question I hadn't yet asked but wanted to confirm!

I'm still sticking with "Major Electrical Fault" as my most likely cause, and this adds to my suspicions.

As I understand it, the landing gear is raised / retracted by electric motor-driven hydraulic pump (pumps?). This/these would create a significant electrical load.

If the plane's multi-redundant electrical system has a fault which is intermittent (the worst kind of electrical issue to diagnose), and which causes the redundancy controls to go haywire (as there are, of course, electronic controls to detect failures and drive the switching over of primary and backup electrical supplies), then this fault could to triggered by a large load coming on-line. It could even be as simple as a high current cable lug not having been tightened when a part was being replaced at some stage. The relevant bolt might be only finger-tight. Enough to work 99.99% of the time between then and now... But a little bit more oxidation, and particularly, a bit more heat (it was a hot day), and suddenly, a fault.

Having worked in electronics for years, I know that semi-conductors (and lots of other components, especially capacitors [and batteries]) can also degrade instead of failing completely. Electro-static discharges are great for causing computer chips to die, or go meta-stable - meaning they can get all knotted up and cease working correctly - until they are powered off for a while. They can also degrade in a way that means they work normally a low temperatures, but don't above a certain temperature.

Anyway, there MUST be ways that the redundant power supplies can be brought down, simply because, to have a critical bus powered from a number of independent sources, there must be "controls" of some sort. I don't know how it's done in the 787, but that's where I'd be looking.

As there is a lot of discussion already about how the bogies are hanging the wrong way suggesting a started but failed retraction operation, and it's now confirmed that the retraction would normally have taken place at about the point where the flight went "pear shaped", I'm going to suggest that the two things are connected. More than that: I'll suggest that the Gear Up command triggered the fault that caused both engines to shut down in very short succession. Nothing the pilots did wrong, and no way they could have known and prevented it.

It's going to be difficult to prove though.

Subjects: Electrical Failure  Gear Retraction  Hydraulic Failure (All)  Hydraulic Pumps

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MaybeItIs
2025-06-14T22:08:00
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Post: 11901884
Originally Posted by BugBear
Difficult!? Maybe not. If very late the flaps were tagged stowed, and there was a simultaneous gear up command, with FlapDown command, the overload could have failed a GCS. Then it becomes a switching exercise. (Automatics).

Alarms Warnings Impacted EICAS, ETC. it happened long ago, but we know what happens when an engine driven generator quits ..
Ahh, thanks! I agree 99%. But if what you say is correct, then isn't this a design flaw? I also don't understand why you'd do Gear Up and Flaps Down at the same time, if the flight was otherwise proceeding normally? But if you're being hypothetical, sure, the pilot might actually be able to induce an electrical failure. I can't comment.

Anyway, let's say we know what's supposed to happen when an engine-driven generator (or its GCS) quits. (Which incident do you refer to?) That's what all the redundancy is designed to address. And maybe that's exactly what did happen - a generator / GCS failed at high load in a high ambient temperature. But possibly the failure then highlighted a pre-existing but undetected fault in the switching system itself. With the generator working normally for (months?), everything seemed fine. Sadly, there are always possibilities that the designers don't consider, or are too hard (too expensive, etc) to address.

Subjects: Electrical Failure  Flaps (All)  Flaps vs Gear  Generators/Alternators

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MaybeItIs
2025-06-15T00:54:00
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Post: 11902008
Originally Posted by FullWings
I think it needs to be said again that pretty much anything can happen to the aircraft systems and the engines will carry on running - this is by design as they have independent FADEC and power supplies and at sea level fuel will get through without boost pumps. You could almost saw the wing off the fuselage and the engine would still produce thrust, TCMA notwithstanding.
Yes, thanks, I've seen a few comments to this effect, and I have to accept most of what you say. I understand that they have their own dedicated generators and local independent FADECs (or EECs), but I'm trying to use what I do know to attempt to figure this out. I know that there are Fuel Cutoff switches in the cockpit. Somehow, if switched to Off, these will cut off the fuel to the engines, "no matter what". Of course, even that's not true, as the Qantas A380 engine burst apparently (comment in this thread) showed.

Anyway, the thing I'm looking at is how the fuel cutoff switch function could have been activated in some other way. To me, it seems obvious that there are wires that run between the engine fuel shutoff valves and the cockpit / flight control panel (no doubt with relays etc in between). I don't know where those shutoff valves are located, but logic says they should be located in the fuselage, not out at the engines. I also don't know how those valves operate - are they solenoid valves or electro-mechanically driven? Nor do I know where the power to activate those valves comes from, but using my logic, if those valves close when powered off, such as solenoid valves typically do, then the power cannot exclusively come from the engine-dedicated generators. If it did, you'd never be able to start the engines so they could supply their own power to hold those valves open. So, there must be some power (appropriately) fed from the main aircraft control bus to activate those valves - if the rest of what I'm assuming is correct. Anyway, like I say, I don't know enough about the details at this point, but there are many more ways to activate or deactivate a circuit than by flicking a switch. Killing the relevant power supply, for example. A screwdriver across some contacts (for example), another. Shorting a wire to Chassis, maybe. Just trying to contribute what I can.

You raise another interesting point: "TCMA notwithstanding". Could you elaborate, please? What will happen if the TCMA system, which apparently also has some degree of engine control, loses power? The problem with interlinked circuits and systems is that sometimes, unexpected things can happen when events that were not considered actually happen. If one module, reporting to another, loses power or fails, sometimes it can "tell" the surviving module something that isn't true... My concern is where does the power to the Fuel Cutoff switches come from? Are there relays or solid-state switches (or what?) between the Panel Switches and the valves? If so, is the valve power derived from a different source, and if so, where? Are the valves solenoids, open when power applied, or something else? What is the logic involved, between switch and valve?

Would you mind answering these questions so I can ponder it all further, please? If I'm wrong, I'll happily say so.

Originally Posted by FullWings
We don\x92t know yet what actually triggered the RAT from the relatively short list but every item on it means there is a serious/critical failure(s). The flight path suggests that it was a double engine failure or shutdown (commanded or uncommanded) as anything else should have left the aeroplane in a poor state but able to climb away.
100%

Subjects: Dual Engine Failure  Engine Failure (All)  FADEC  Fuel (All)  Fuel Cut Off Switches  Fuel Cutoff  Fuel Pumps  Generators/Alternators  RAT (All)  TCMA (All)

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MaybeItIs
2025-06-15T04:00:00
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Post: 11902086
Originally Posted by Someone Somewhere
Gear and flaps are both hydraulic, and the hydraulic pumps typically act as effective fault-containment - a hydraulic failure or excess load doesn't result in excess demand on the electric side; the pump just starts to run out of output flow/pressure.
Ok, thanks for clarifying. Of course, an overload will simply cause the hydraulic pressure relief valves to activate. There will be a moderate increase in motor current when bypassing, but the electrical side should be fully able to cope with that. Should be! I'm suggesting here that there was a fault somewhere in the electrical supplies that effectively derated some part of it, and that maybe the GearUp load was too much for it on this occasion.

Originally Posted by Someone Somewhere
In addition, the 787 has four main generators and I believe the switching is segregated into at least two controllers, on top of the four separate generator control units.
Thanks for confirming the 4 gens. So there's probably quite a bit of switching required. Not sure how that's done, but I guess robust contactors are required. And even these can fail. Systems usually cannot tell that a contactor has failed on the open side until it's switched. So, a switchover may have been done, but a failed contact meant the backup generator wasn't connected. Who knows, so many possibilities.

Originally Posted by Someone Somewhere
And again, electrical failure should not cause engine failure - consider QF32 where the wiring to the engine was mostly severed and they had to drown it with a fire truck.
Sure, I agree, absolutely shouldn't. Yeah, the A380... Possibly (I suggest likely), the A380 uses different logic from the B787. In the Airbus case, maybe they prioritised keeping the fuel on over shutting it off in emergency. So, severing the Airbus Cutoff signal leaves the fuel on. Boeing may use the opposite priority, that Emergency Shutdown takes precedence over Engine Running, so cutting the signal turns the engine off. I don't know, but don't think the Airbus incident necessarily applies here.

Originally Posted by Someone Somewhere
It's not. Boost pumps should be more-or-less unnecessary at sea level.
I don't think either of us was debating that. I accept it as a fact.

Originally Posted by Someone Somewhere
I believe the valves are almost all bi-stable power-open power-close. When not powered, they remain in the last commanded position.

The valves are located in the spar (hence being called 'spar valves'. The fuel tank is immediately above the engine so it is a very short pipe for suction feeding. Tail mount engines are potentially a different story...
Okay! Many thanks for that! Of course, it very much complicates the picture, and I'm very puzzled as to how the Fuel Cutoff Switches and Valves operate. Apparently, the TCAM system shuts off an errant engine on the ground at least, but my concern is not with the software but the hardware. It obviously has an Output going into the Fuel Shutoff system. If the TCAM unit loses power, can that output cause the Cutoff process (powered by the engine-dedicated generator) to be activated? I guess that's the $64 billion question, but if MCAS is any example, then: Probably!

Subjects: Electrical Failure  Engine Failure (All)  Flaps (All)  Flaps vs Gear  Fuel (All)  Fuel Cut Off Switches  Fuel Cutoff  Fuel Pumps  Generators/Alternators  Hydraulic Failure (All)  Hydraulic Pumps

MaybeItIs
2025-06-15T06:09:00
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Post: 11902135
Originally Posted by Icarus2001
No evidence of engine failure

No evidence of RAT deployment from a poor image.

No evidence of electrical failure.

The teams of lawyers in the UK representing 53 grieving families will be working over the weekend to sign up said families to a class action.

​​​​​​​This is going to get messy.
​​​​​​​
I guess it all depends on what you mean!

If the fuel supplies were cut off, causing the engines to stop, is that engine failure ? I'd say not, nothing wrong with the engines until they impacted the buildings etc.

No evidence of RAT deployment - but you're specifically restricting "the evidence" to a blurry amateur video. That alone is not great evidence, but why does that video exist at all? When they lift the relevant section of fuselage, RAT deployment or not is going to be fairly apparent. And Circumstantial evidence is still evidence, no?

No evidence of electrical failure? Do you know that from the downloaded Flight Data?

Subjects: Electrical Failure  Engine Failure (All)  Fuel (All)  Fuel Cutoff  RAT (All)  RAT (Deployment)

MaybeItIs
2025-06-15T06:47:00
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Post: 11902155
Originally Posted by tdracer
I hate to disappoint you, but the people (like me) who design, test, and certify aircraft are not idiots. We design for failures. Yes, on rare occasion, something gets missed (e.g. MCAS), but we know that aircraft power systems sometimes fail (or suffer short term interuptions) and we design for that. EVERY VALVE IN THE FUEL SYSTEM MUST BE POWERED TO CHANGE STATE!!!! If electrical power is lost, they just stay where they are. The engine fuel valve must be powered open, and it must be powered closed. Same with the spar valve. The pilot moves a switch, that provides electrical signals to the spar valve and the engine fuel valve to open or close. It's not complicated and has been in use for decades.
TCMA (not TCAM) - Thrust Control Malfunction Accommodation - is a FADEC based system. It's resident in the engine FADEC (aka EEC) - the ONLY inputs from the aircraft that go into the TCMA is air/ground (to enable) and thrust lever position (to determine if the engine is doing what it's being commanded to do. The FADEC has the ability to shutdown the engine via the N2 overspeed protection system - this is separate from the aircraft run/cutoff signal, although it uses the same HPSOV to effect the shutdown. That same system is used by TCMA to shutoff fuel if it determines the engine is 'running away'.

Hint, you might try going back a few pages and reading where all this has been posted previously.
Hi tdracer, and thanks for your comments.

I hope I never suggested you guys are idiots! I very much doubt that indeed. You cannot be idiots. Planes fly, very reliably. That's evidence enough.

Maybe my analysis is simplistic, but for someone who knows as little about the nuts and bolts that are your profession, I think I'm not doing too badly.

I believe I have made a number of worthy contributions to this thread. Maybe I'm deluded. Too bad. Fact is, over the history of modern aviation, there have been a number of serious design stuff ups that "shouldn't have happened". As far as I'm concerned, the crash of AF447 is bloody good evidence of not considering a very simple, fundamental failure, and should NEVER have happened. The thing is, that would have been sooo easy to avoid. So please, don't get on too high a horse over this.

Thanks for your information about all the fuel control valves. That's cool. Yes, my cars have numerous such systems, from the radiator grilles backward.

And you misunderstand what I meant about "complicates things". Was that deliberate? What I meant was it complicates understanding how a major electrical failure could cause the Fuel Cutoff valves to close, that's all. The valves don't close if unpowered, but if the control is via the FADEC, then what could have caused them to close?

Your explanation of how the Fuel Valves are controlled is rather simplistic too. "The pilot moves a switch, that provides electrical signals to the spar valve and the engine fuel valve to open or close." Seriously? Am I an idiot then? Is it a single pole, single throw switch? Is the valve driven by a stepper motor, or what? A DC Motor and worm drive? Does it have an integral controller? How does the valve drive know when to stop at end of travel? Would you mind elaborating, please?

Subjects: Electrical Failure  Engine Over-speed (All)  Engine Shutdown (Over-speed)  FADEC  Fuel (All)  Fuel Cutoff  High Pressure Shutoff Valve  N2 Over-speed  TCMA (Air-ground Logic)  TCMA (All)  TCMA (Shutdown)

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MaybeItIs
2025-06-15T10:12:00
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Post: 11902322
Originally Posted by JunkAccount
This is probably a very stupid question, but what would happen if a BPCU fault (or other cause) led to VFSGs on opposite sides of the aircraft being connected to the same 230 VAC bus?

My understanding is that the left engine VFSGs are not synchronized in frequency or phase with the right engine VFSGs. Cross-connecting them, electrically, could be quite violent from both an electrical and mechanical perspective.

Is it realistically possible that the torque shock from cross-connected VFSGs could damage their associated accessory drive trains to the extent that the associated FADEC alternators would no longer make power? In this situation, there would be a loss of aircraft electrical power due to the BPCU fault, no FADEC alternator power due to damage to the accessory drive train, and, therefore, no engine thrust.

I presume each VFSG has a frangible link to protect the accessory drive train in the event the VFSG seizes up, which ought to make this loss-of-engine-thrust scenario impossible, but presumption is not knowledge, and this is a possible failure chain that doesn't involve stacking up multiple 10e-9 events.
From my POV, this is not a silly question at all.

In fact, I have inadvertently "done" such a thing - all I did was switch the generator room light from one genset to the other. But whoever installed that cheap and nasty two way light changeover switch didn't realise that it sometimes did a make-before-break transfer. There was a BANG and everything instantly went dark. Every single circuit breaker on the switchboard tripped. To this day, I still don't understand why all the Load Circuit Breakers tripped as well as the generator output breakers, and no one has really supplied a clear answer. Of course, any inductive loads connected at the time would cause that, but simple incandescent light circuits? Would a couple of hundred meters of underground power cable have enough inductance to cause a breaker trip?

Anyway, Yes, the results were very dramatic, and these were only a pair of 10-15kVA Single Phase 230V gensets. If this happened on that plane with 225KVA(?) generators at a couple of hundred feet in the air, I'd imagine they had no chance of recovery. Could it happen? If something had been wired up incorrectly in the transfer circuits, I'd say Yes. When a fault-related transfer occurred.

Still doesn't explain what could have stopped the engines, but sheared shafts would have done it, as you say. That would be pretty strong evidence.

Now, if it's true that this plane had been scavenged for parts at some stage, all the couldn't happens probably evaporate. I'd guess...

Subjects: FADEC  Generators/Alternators

MaybeItIs
2025-06-20T09:24:00
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Post: 11906767
Originally Posted by Musician
"Both engines failed or shut off close to rotation" explains all of the evidence : it explains an unremarkable take-off roll, loss of lift, absence of pronounced yaw, loss of electrical power, loss of the ADS-B transponder, RAT deployment, the noise of the RAT banging into place and revving up, emergency signs lighting up, a possible mayday call reporting loss of thrust/power/lift, and a physically plausible glide from a little over 200 ft AAL to a crash site 50 feet (?) below aerodrome elevation.
Isn't "close to rotation" a little broad? "Close to" can be before or after. If before, and with about 4,000 feet of runway remaining, why did they take off at all? How did they take off, for that matter?

Can anyone do the Momentum / Energy calculations to work out how high the plane would have travelled at the normal climb gradient purely on the momentum it had at rotation? I'll try, see how far I get. A stone, fired into the air at an upward angle, begins to slow down and curve towards the earth the moment it leaves the catapult. It appears to me that the plane climbed at approximately a steady speed until about the 200 ft mark, so I submit that it had adequate climb thrust up to "about" that point.

Which, as confirmed in the earlier thread, is about where GEARUP is typically called. I say those two events are linked, led by GEARUP, but it could be coincidence. Though I don't think so. Coincidence usually refers to unrelated events and that would be very hard to say, here.

On that point, the gear, as far as I can establish (not openly published according to Google), weighs around 8-odd to 10 tonnes. Typically, retracts in about 10 seconds. I estimate it's no more than a 2 metre lift. As far as I can work out (using 3m to make the value higher), that requires about 30kW (rough estimate, budgetary figure, not accounting for it being a curved path, so it's probably higher closer to fully up), but whether wind pressure affects it, I have no idea. Anyway, 30kW isn't a huge (additional) load on a 225kVA alternator. Less than I'd imagined.

Now I'm wondering how big (power ratings) the hydraulic pump and motor are? No doubt, they're driven by a VSD. Can anyone comment, please?

Last edited by MaybeItIs; 20th Jun 2025 at 09:37 . Reason: Oops, numbers mixed up...

Subjects: ADSB  Engine Failure (All)  Engine Shutdown  Generators/Alternators  Hydraulic Failure (All)  Hydraulic Pumps  Mayday  RAT (All)  RAT (Deployment)  Takeoff Roll

MaybeItIs
2025-06-20T11:21:00
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Post: 11906857
Originally Posted by Musician
It would definitely be nice to narrow that down; I can't do it, and your method is not convincing me.
I'd agree, without expert knowledge there would have to be big assumptions, but I expect that Aircraft Flight Engineers could do it. Probably already have.

The ADS-B datagrams sent by the aircraft show a much diminished climb rate with decaying speed, betraying insufficient thrust in that phase of the flight. That somewhat contradicts your assertions.
Sure, actual data is usually more accurate than eyeballed stuff. But not always. In fact, it's often the eye that determines that something measured or calculated is "Off". How accurate is ADS-B data? I've seen FR24 tracks go way off course then suddenly get corrected / interpolated, frequently. The erroneous data seems to be "removed" by their algorithm, but where are the errors arising? Why this inaccuracy, and therefore, how accurate are the datagrams referred to? I know there were no datagrams received during the backtrack that I accept actually occurred, but that's completely different from receiving erroneous ADS-B data.

I also do not have faith in anyone's ability to watch the cctv video and confidently determine through mere eyeballing that the climb rate did not decay by 15% within the first 100 feet or so.
Sure, the CCTV footage I've seen is very poor, a video, moved about and zoomed, of the CCTV screen. Not easy to judge, but still useful and could be analysed frame-by-frame to compensate for all the extraneous input. Anyway, it's obvious to me that the rate of climb dropped abruptly just before the flight attained its apex, as if thrust was suddenly cut off. Knowing the momentum to altitude conversion, it might be possible to estimate whether that's true or not. The evident RAT deployment supports engine shutdown, not just engines to Idle, doesn't it? In that case, it would be useful to know at what altitude the engine shutdown took place.

(The ADS-B data suggests the speed diminished 7% for ~50 ft of climb.)
Okay, didn't know that, I guess suggests means it's uncertain? Can you tell me from what height to what height it suggests this?

And why all the wrong figures for the height attained, quoted in previous thread? Can't all be the atmospheric conditions.

Other than your stone, even a glider can convert speed to altitude.
Haha! Even a stone (the right shape) can do that, and I'm not disputing that kinetic energy can be converted to altitude. Wings are useful for that... Just curious to get an idea of how much in this case.

To be honest, i believe that taking a lot of the evidence into consideration, it is possible to arrive at a limited number of scenarios for what is most likely to have happened.

One fact that alters things substantially is whether the survivor's impression is correct that possibly the engines started to spool up again just before impact. If that's the case then what does that do to the possibility or otherwise that the TMCA system caused a dual engine shutdown?

To me, since the world seems to be watching this forum, and we are getting no feedback from the authorities, what is posted here might be useful in helping the investigators look at things they might not have considered. Besides, as Icarus2001 has kindof suggested, it's probably a very good thing that there are clearly lots of keen eyes on this.

Last edited by MaybeItIs; 20th Jun 2025 at 11:29 . Reason: Missing [/QUOTE]

Subjects: ADSB  CCTV  Dual Engine Failure  Engine Failure (All)  Engine Shutdown  FlightRadar24  Fuel (All)  Fuel Cutoff  RAT (All)  RAT (Deployment)

1 user liked this post.

MaybeItIs
2025-06-20T13:47:00
permalink
Post: 11906986
Indeed, thanks to you for your most informative reply! Great to know we're much on the same page.

I'll strive for brevity here. [Fail, sorry!]

Originally Posted by Musician
When that happens, the live display of FR24 assumes the aircraft kept doing what it did, ... FR24 then connected these points via the shortest route;
Aha! Very misleading by FR24! Maybe they can devise a way to show where data is missing.

However, the datagrams that FR24 actually received were correct. They contain the GPS position of AI171 and its unadjusted barometric altitude, as determined by its onboard instruments. This data is as reliable as the instruments themselves are.
Sorry, I got confused about this ^^^, when you wrote this:

It's uncertain because the 787 rounds all altitudes it sends to the nearest multiple of 25. The altitudes sent were from 575 ft to 625 ft.,
but I'm assuming reliable within the 25ft granularity that the 787 creates, which mostly is neither here nor there, but in this case, not so helpful!

The RAT deploying is a consequence of a dual engine shutdown. It says nothing about whether the TMCA was involved.
Yes, got it, but wasn't what I was meaning to ask, sorry. My bad. I'm about over this TMCA stuff because it sounds like it's Trade Secret so a lot of guesswork, but the question I was intending was:

If the TMCA did activate and shut off the fuel for whatever reason, what causes the TMCA/FADEC Hardware (and Software) to Reset, since it's independently powered off the engine-driven PMG after engine start? There is so much here that is just so unclear. I haven't seen anything about a Reset input anywhere, and since it's supposed to work only when on the ground, that's not really necessary, as the engine will eventually spool down. At some point before that, the PMG output voltage will go to low enough that the FADEC/TMCA should be forced into a Hardware Reset. That's all fine on the ground, but in the air, the engine will windmill, potentially until.... Is the PMG output fed through a switch/relay that cuts the FADEC/TMCA supply at low (i.e. windmill) RPM, so that a Pilot-activated Engine Off/On cycle can reconnect the Aircraft FADEC Supply link, thus Rebooting the FADEC so that it reopens the Fuel Shutoff valve(s)? It all seems so "awkward". And potentially fatal. Is this a scenario that the designers considered? (Who can answer that one? )

Just now, I realise that if this is roughly what happens, then maybe the engines did commence a restart just before impact, due to the plane being deliberately mushed/stalled to the ground as softly as possible, thereby reducing the windmill RPM. And maybe the engines restarting interfered with that planned landing.

Or maybe I've got this all wrong. I'm hoping someone will tell us all.

[Now I just hope your post is still there as I post this. ]
Thankfully, Yes. Hope this Reply gets through too.

Subjects: AI171  Dual Engine Failure  Engine Failure (All)  Engine Shutdown  FADEC  FlightRadar24  RAT (All)

1 user liked this post.

MaybeItIs
2025-06-20T22:57:00
permalink
Post: 11907382
Originally Posted by Crossky
Hello, this is my first post on pprune; as a 787 pilot I\x92m also puzzled by this accident. All seem to agree that for some reason there was a complete electrical failure and RAT deployment. With a complete electrical failure all six main fuel pumps fail. Each engine also has two mechanically driven fuel pumps. On takeoff, if there is fuel in the center tank, it will be used first, pumped by the two center tank pumps.
My airline\x92s manuals don\x92t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren\x92t able to suction feed well enough from the center tanks to sustain engine operation. If there was fuel in the center tanks, a complete electrical failure would soon lead to center tank fuel pumps failure (all fuel pumps failure as stated previously) and fuel starvation of both engines. A rescue from this situation would be an immediate selection of both center tank fuel pumps OFF (not if my airline\x92s non-normal checklists) and waiting for successful suction feed from the L and R main tanks to occur, this would take a number of seconds.
Great first post (IMMHO!) If this is correct, then I think you are onto something very significant. No expert, just an outside the box thinker who has been trying to see what ordinary (non-pilot-blaming) explanations there could be for a near simultaneous dual engine failure. I imagine a complete electrical failure leading to fuel starvation from lack of pump feed pressure from the centre tank would not result in apparently near simultaneous engine failure, but who knows? (Aren't there (suction) bypass valves here, but maybe they get stuck after long non-opening - instead long subject to closing pressures?) This could have been the case here as my experience suggests the probabilities aren't small.

FWIW, according to earlier posts, the fuel load was about 50T, leaving about 18T in the centre tank, so (I think) about 25-30% full. A full centre tank might allow engine pump suction to work fine, but this might not? (Contrary to what some have said.)

Anyway, FWIW, not everyone agrees with RAT Deployment - see recent post by shep69. Would love to know why he doesn't go with RAT deployment...

Subjects: Centre Tank  Dual Engine Failure  Electrical Failure  Engine Failure (All)  Fuel (All)  Fuel Cutoff  Fuel Pumps  RAT (All)  RAT (Deployment)

MaybeItIs
2025-06-21T01:21:00
permalink
Post: 11907432
Originally Posted by Aerospace101
For those postulating the RAT was not deployed, what counter explanations do you have for the following clues?
  • Distinctive RAT sound in the rooftop video, audio analysis here .
  • RAT visible in rooftop video, example in this image .
  • APU door open suggesting auto APU start, suggestive of a full electrics failure (one of the criteria for auto RAT deployment)
  • Loss of ADSB data suggestive of a full electrics failure (one of the criteria for auto RAT deployment)
  • Unusual gear forward tilt position, suggestive of hydraulic failure and/or full electrics failure (one of the criteria for auto RAT deployment).
  • Loss of all thrust, ie dual engine failure (one of the criteria for auto RAT deployment)
Great summary. I've already mentioned the first below, but I'd add another:
  • The existence (and timing) of the flyby video by a young lad who apparently lived where the footage was shot from. With planes flying past every few minutes, why would he choose to film this one, before he could even see it? The video starts with the plane still approaching, out of view, and his position suggests it was unplanned, before he could move to a better vantage point. I say he already knew it was extraordinary - from the sound.
  • Eye witness account from the mother of the lad who filmed the flyby, apparently said that the plane was "shaking". I'll assume she didn't know how to describe it properly, and that maybe it sounded like it was shaking, from hearing the noise from the RAT. Or it's a translation issue of a word/s with multiple meanings or used colloquially.
One question - are there two exterior doors to the APU compartment, one on top, one below, presumably inlet and outlet of cooling airflow? I've seen photos showing two open doors, but the lower one could be something else, and busted open during the crash.

Subjects: ADSB  APU  Audio Analysis  Dual Engine Failure  Engine Failure (All)  Hydraulic Failure (All)  MLG Tilt  RAT (All)  RAT (Deployment)  RAT (Sound)

1 user liked this post.

MaybeItIs
2025-06-22T23:35:00
permalink
Post: 11908907
Originally Posted by FullWings
That\x92s the nature of a common mode bug. If the software was vulnerable to Mars being in the house of Uranus, the scent of lilacs and the DOW being less than 42,000 then you\x92d expect the failure to occur everywhere when these conjoined. Same when an aeroplane\x92s systems and/or the environment present data that triggers an unplanned/unforeseen response in something like an EEC/FADEC. The experts still appear to think that this is unlikely but we have been presented with an unlikely occurrence...
I have to both agree and disagree with both this and the next post by TryingToLearn.

Yes, there may be (let's assume is) "identical" FADEC/TCMA hardware and firmware on both engines, but if the Left Engine is subject to Mars in the house of Uranus (wink wink), then the Right Engine cannot be, maybe it's Venus in the same House. This is simply because the Left engine TCMA 'contraption', I'm going to call it, is monitoring Left Engine Conditions (Shaft Speed, T/L setting / position data - Right or Wrong, and calculating and comparing accordingly against its internal map) while the opposite TCMA "device" is monitoring and calculating etc, Right Engine Conditions. There are some things in common, but (I say) it's virtually impossible for the Engine Conditions being individually monitored to be identical in both engines.

The Thrust Levers are electro-mechanical devices, almost certainly at this stage pushed by a somewhat squishy human hand, likely with a slight offset. What is the probability that those two levers are in identical positions, and even if they are, that the calibration (e.g. "zero points") of both levers are identical, and that the values they output (response slopes/curves) are exactly matching in every matching point in their individual travels? That's just one aspect, but consider the engines. They are different ages. Have different amounts of wear. They have separate fuel metering valves (or other names), separate HP Fuel pumps (and, I guess relief valves?), all also subject to wear), and each has a host of other, correspondingly paired, sensors, (maybe of different makes and certainly of different ages and different calibrations and response curves) from which each FADEC, supposedly independently of the TCMA, adjusts the fuel metering device settings and resulting engine power, and shaft RPMs follow in some other slightly non-matching way.

Sure, I would completely agree that the two engines and their calculated Throttle Lever positions to Shaft RPMs are always going to be similar during normal, matched operation, and they will very likely dance with each other, maybe one 'always' (75% of the time, say) leading during one dance (TO, say) with the other leading in dancing to a different tune (descent, say).

To me, the fact that this appears to have been an almost simultaneous dual engine failure, pretty much, for me, rules out a FADEC/TCMA firmware bug, especially as there don't seem to be any reports of even a single engine mid-air TCMA shutdown.

HOWEVER, and I want to stress this, that doesn't rule out the possibility that both TCMAs shutdown their respective engines simultaneously. Any lack of simultaneity observed would be due to those slight differences in other pieces of hardware, such as the time for one Shutoff valve to close versus the other.

As far as I know, there isn't enough information on what's actually inside those TCMA Black Boxes to say anything for sure, but here's a thought, which I think has been alluded to, or the question asked, here in one or other thread, earlier.

What does the TCMA firmware do when an engine is already running at a high power setting and TWO things occur in quick succession? I suspect this kind of event is a highly probable cause, but these two events have not occurred close enough together, or ever, before.

Imagine this: Plane taking off, Throttle Levers near Full Power, Engines performing correctly, also near Full Power, Rotation etc all normal, plane beginning to climb, positive rate achieved.

Pilot calls GEARUP. GearUp, activated.

The Gear Retract sequence begins. Due to some unforeseen or freshly occurring (maybe intermittent short or open circuit) linkage between the gear Up sequence and the WOW or Air/Ground System, the signal to both TCMAs suddenly switches to GROUND. All "good", so far, as the engine RPMs match the Throttle Lever settings and TCMA doesn't flinch. The plane could be in a Valid Takeoff sequence, so it had better not! But it does make a bit of sense. How is WOW / Air/Ground detected? Somewhere near the Landing Gear, I assume.

HOWEVER, now, a moment later, and perhaps due to a related system response, the Thrust Levers suddenly get pulled back to Idle, whether by man or Machine.

What would you expect the TCMA system to do? I would guess, fairly soon thereafter, two, independent, Fuel Cutoffs... Though I fully admit, I'm guessing based on a severe lack of knowledge of that Firmware.

Ok, no need for further explanation on that point, but I did refer to TCMA unflatteringly as a contraption, earlier. Last night (regrettably, before bed) I started looking at the TCMA Google Patent. Let's just say, so far, I'm aghast! My first impressions are bad ones. How did this patent even get approved? What I suspect here, now, is not a Firmware bug, but a serious Logic and Program Defect. But we'd have to see what's inside the firmware.

When I get more time, I'll dig deeper.

Subjects: Dual Engine Failure  Engine Failure (All)  FADEC  Fuel (All)  Fuel Pumps  Gear Retraction  TCMA (All)  TCMA (Shutdown)

1 user liked this post.

MaybeItIs
2025-06-28T03:40:00
permalink
Post: 11912314
In response to removed posted video link about drifting ADs since 2022, not finished yet but remarkably, seems to be 100% accurate:

https://www.federalregister.gov/docu...pany-airplanes

https://www.federalregister.gov/docu...pany-airplanes

Actually, I have a little experience with this too. More commonly a male-related problem, but that "water" that could seep through from the lav floors into the EE Bay(s) is often highly conductive, if ya get my drift? Water has an absolutely amazing ability to track and seek. Add some electrolytes and it's often even better.

Last edited by MaybeItIs; 28th Jun 2025 at 03:42 . Reason: Alter for removal of click-bait post

Subjects: None

MaybeItIs
2025-06-28T03:55:00
permalink
Post: 11912318
Originally Posted by Capn Bloggs
I'm not suggesting he's wrong about the ADs, I'm just saying that water in the avionics bay (which I'm sure has been brought up already) is pure speculation.
...by the FAA

"This AD was prompted by reports of water leakage from the potable water system due to improperly installed waterline couplings, and water leaking into the electronics equipment (EE) bays from above the floor in the main cabin, resulting in water on the equipment in the EE bays"

Subjects: Air Worthiness Directives  FAA  Water Ingress