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Chiefttp
June 18, 2025, 00:09:00 GMT permalink Post: 11904785 |
also see in the final moments of desperation, reaching down and turning the Fuel Control Switches, OFF-THEN-ON, in the hope that an engine will come to life, if they believed that the engine was dead. This may be the reason the RAT extended? Just thinking out loud. |
PPRuNeUser548247
June 18, 2025, 12:18:00 GMT permalink Post: 11905193 |
I wonder if the delay in announcing any preliminary findings is because of the enormity of the consequences.
Let us say the investigation team have discovered a unique technical fault that caused the accident, but don’t yet know why it happened, how would the team proceed? On the one hand they’ve uncovered a fault which could reoccur and cause another accident (but a fault that has only happened once in 14 years). On the other hand a grounding would have enormous commercial consequences worldwide, with the possibility that an inspection and/or rectification are not yet available. What would they do? As I said in a previous post, every day that passes without a EAD suggest the cause was was specific to that aircraft (fuel contamination, maintenance failure, crew error - pick you own theory) Last edited by PPRuNeUser548247; 18th June 2025 at 12:43 . |
Someone Somewhere
June 18, 2025, 13:08:00 GMT permalink Post: 11905228 |
I (and I think everyone else here) have been assuming that the FADEC does in fact have a dedicated permanent-magnet alternator, as is the case on the Airbuses (confirmed by FCOM) and surely the 737.
I have been told elsewhere that this is not the case. A read of the draft FCOM available online for the 777 & 787 makes no mention of a FADEC generator, but then neither does the 737 manuals. Is this simply a case of "Boeing thinks you don't need to know"? It has been proposed that the primary source of power for the FADECs is actually the flight control PMGs, mounted on the engine gearbox, but that this power goes to the avionics bay, has failover switching gear, and comes back to the EEC. Can anyone shed concrete light on this (e.g. a source that clearly states there is both an EEC alternator and a flight control PMG on the accessory gearbox)? Alternator and generator seem to be used interchangeably in this context. I don't think you'll find an actual wire list for it (or it won't be useful) as apparently most/all of the data is via an ARINC bus. I attempted to PM this but your inbox is full. [SLF with an electrical background and some exposure to ground-side critical facilities power] Last edited by Someone Somewhere; 18th June 2025 at 13:32 . |
FullWings
June 18, 2025, 13:12:00 GMT permalink Post: 11905236 |
Given that there are >1,100 787s in service, you would be losing a significant part of the World\x92s air transport infrastructure if you grounded them. Also, if you\x92re still nowhere near understanding what caused it, how would you \x93unground\x94 the fleet if you don\x92t get answers for some time? It\x92s obviously something rare/unique, given the 14 years of operation without such an accident, so statistics should be on your side if you did nothing until you had more surety as to where the problem(s) lay? |
WillowRun 6-3
June 18, 2025, 15:45:00 GMT permalink Post: 11905345 |
A case in point is the 2013 Boeing 787 battery fires. After two thermal runaways in 52 000 flight-hours, the root cause was still unknown; however, the FAA nevertheless issued Emergency AD 2013-02-51 grounding every 787 until a modification was available. IMHO a risk where the outcome is catastrophic, even very low probability, would trigger the FAA to issue an Emergency Airworthiness Directive as per their policy.
As I said in a previous post, every day that passes without a EAD suggest the cause was was specific to that aircraft (fuel contamination, maintenance failure, crew error - pick you own theory) At this time, the fault or flaw at the root of this accident and how that fault or flaw worked through aircraft components and systems has not been identified publicly. It might not even have been identified .... I'm not convinced that separating "what" from "how and why" as a semantics exercise is enough to conclude the Annex 13 officials know the root cause yet. Maybe they do, maybe not. And if they do not, then the contrast with the situation where FAA was, it seemed, keeping a close eye on battery issues in particular, is relevant. |
adfad
June 18, 2025, 18:18:00 GMT permalink Post: 11905444 |
To my mind, this points to a potential software issue. 787s have already suffered from 2 separate software issues in which the passage of time causes a major and possibly catastrophic failure - the need to reboot systems before 51 days and 248 days have elapsed, due to poorly-written software. Given that history, the probability of there being a third, previously-unidentified but broadly similar in nature software issue seems surprisingly high. They aren't independent variables.
Such a passage-of-time software issue wouldn't show up in most (or possibly any) testing scenarios. It is the sort of issue that robust QA and static code analysis are designed to catch. But in at least two separate systems on the 787 it has not been caught prior to software shipping. Meanwhile, every new technical post demonstrates the myriad ways in which non-software potential causes are mitigated by redundant design. The odds of two (or more) redundant mechanical systems failing in precisely the same way at precisely the same moment are very, very small. The odds of identical software on two (or more) redundant systems reaching a passage-of-time bug at precisely the same moment are, by contrast, very much higher. True redundancy would require different software on each redundant sub-system. Integer overflow is a specific type of issue common to many systems, but like you said - it is something that should be found with robust QA and analysis. The ability to shut down all generators at once from a single source seems like a risky design decision to me and I agree with your point about different software on 2 or more redundant sub systems. My theory is that this was an accepted risk because the engine-driven fuel pumps would be more than enough in most phases of flight to keep the engines running, and you would still have 2 engines for redundancy. The APU would also restore AC power in lets say 30 seconds and you would then have electric fuel pumps as well. I think there are several factors that could explain how loss of all AC power during takeoff could lead to a crash:
Last edited by adfad; 18th June 2025 at 18:36 . |
rigoschris
June 18, 2025, 18:25:00 GMT permalink Post: 11905452 |
We have two donks individual fuel supply cut simultaneous in split seconds. There is no rudder activity visible for any thrust asymmetry during this timeframe. TCMA is implemented via the FADECs which are independent for each engine with their own power source from each engine. TCMA is designed to shut down its engine if its power lever is in retard position and the engine is still powering with too much thrust. In addition the airplanes ground sensors must indicate that it is on the ground. For each thrust leaver there are two independent position sensors. It is similar redundant designed as in modern car acceleration pedals. A dual redundancy in each thrust leaver. For TCMA to shut down two fuel supplies within split seconds we have to assume that 4 thrust leaver sensors malfunctioned and the ground sensing logic failed at the same time. The probability that this happens is nil (may be 1 in every 10exp15 hours) which would be about 10 times the age of our universe.
Unless there is a software error in the FADEC TCMA system which only came to light on this flight. But there seem to be nothing special on this flight until rotation. If there is a software error I expect, that we get false single engine shut downs first. And that would already made the news if it happened during rotation. So, from my understanding, if there is an issue with some of the throttle position sensors, the FADECs will detect a disagreement and keep the high thrust -> assume safe is "fly", whereas one of the TCMA channels might read or misinterpret throttle position close to idle. As the thrust doesn't decrease, at some point the upper bound of the falling TCMA thrust contour will be breached and the engine will be shut down. Last edited by rigoschris; 18th June 2025 at 20:09 . Reason: Rephrase potential interplay of TCMA with rest of FADEC logic |
Gino230
June 18, 2025, 18:38:00 GMT permalink Post: 11905461 |
This isn’t the first one either. On February 9, 2024 a Challenger 600 manuevering to final at Naples FL, (APF) lost both engines simultaneously and crashed on a highway short of the runway. The NTSB final report isn’t out yet so we don’t know that cause either, but the situation was the same. SOMEhow, a highly experienced crew found themselves in a situation from which there was apparently no escape. Whatever the cause was, how did it go un-detected until it produced an accident? (It’s NTSB accident number ERA24FA110. You can find that thread on PPRUNE by searching on Challenger 600. The preliminary NTSB report contains interesting readouts from the FDR. Yes, they lost both fans simultaneously.) I’m not suggesting these two accidents have related causes, I’m only observing that both crews apparently had no way out.
My condolences to all who were lost. Please keep in mind that except by the grace of God it could have been any one of us on that terrible day. NASA retired, licensed since 1971. But I agree that the complete, simultaneous loss of thrust on both engines has to be an astronomical probability, and the cause is going to be interesting to say the least. I also agree that any one of us could be put in a horrible position within seconds that would be very hard to recover from- the older I get and the more hours I spend in the air, this starts to spend more time in one's consciousness, unfortunately. BTW calling the crew " highly experienced" is a bit of a stretch IMO, the Captain certainly was, but 1100 hours isn't even enough for an ATP in most countries. For all we know it was not a factor, of course. PS, what is an SLF?? |
EDLB
June 18, 2025, 19:15:00 GMT permalink Post: 11905486 |
@syseng68k
Consensus here is, that both engines where stopped by a closing fuel cut off valve, wich yields a fast loss of N2. The generators then shut down very quick as does the thrust in a few seconds. This is supported by the quick RAT extension which allowed the crew to control the flight. The APU did autostart too. A thrust changed with the thrust leaver to idle is much slower and would not result in the dramatic change in performance. Thrust set to idle will not engage the RAT since the electric generators would still work. So a thrust leaver changed to idle or any intervention by Autothrust (AT) would not yield to the RAT extension. Something or someone activated a fuel cut off. How and why that happened is the big question, the investigators have to answer. |
Nick H.
June 18, 2025, 21:30:00 GMT permalink Post: 11905563 |
@syseng68k
Consensus here is, that both engines where stopped by a closing fuel cut off valve, wich yields a fast loss of N2. The generators then shut down very quick as does the thrust in a few seconds. This is supported by the quick RAT extension which allowed the crew to control the flight. The APU did autostart too. A thrust changed with the thrust leaver to idle is much slower and would not result in the dramatic change in performance. Thrust set to idle will not engage the RAT since the electric generators would still work. So a thrust leaver changed to idle or any intervention by Autothrust (AT) would not yield to the RAT extension. Something or someone activated a fuel cut off. How and why that happened is the big question, the investigators have to answer. ![]() |
Surlybonds
June 18, 2025, 21:47:00 GMT permalink Post: 11905569 |
The fuel cutoff switches can't be "flipped" in either direction; they have to be lifted over a detent and then moved, a very positive action.
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777ret
June 18, 2025, 22:38:00 GMT permalink Post: 11905597 |
@syseng68k
Consensus here is, that both engines where stopped by a closing fuel cut off valve, wich yields a fast loss of N2. The generators then shut down very quick as does the thrust in a few seconds. This is supported by the quick RAT extension which allowed the crew to control the flight. The APU did autostart too. A thrust changed with the thrust leaver to idle is much slower and would not result in the dramatic change in performance. Thrust set to idle will not engage the RAT since the electric generators would still work. So a thrust leaver changed to idle or any intervention by Autothrust (AT) would not yield to the RAT extension. Something or someone activated a fuel cut off. How and why that happened is the big question, the investigators have to answer. |
sycamore
June 18, 2025, 22:49:00 GMT permalink Post: 11905602 |
As an ex-tp, I would consider those cut-off switches a danger, and they should have guards either side of each.
Shirtsleeves/watches etc. can get caught, lift switch. Very poor design. Would not pass `military-muster.` Last edited by T28B; 18th June 2025 at 23:12 . Reason: Fixed your punctuation. |
OldnGrounded
June 18, 2025, 23:16:00 GMT permalink Post: 11905612 |
They're guarded by the switch design/operation itself. To move one of them, the toggle handle has to first be pulled outward.
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bbofh
June 19, 2025, 01:30:00 GMT permalink Post: 11905658 |
The 787-8 landing gear retraction is primarily hydraulic, using the center hydraulic system for the main operation. However, the alternate gear
extension
system utilizes a dedicated electric pump to pressurize fluid from the center hydraulic system for gear extension. Obviously due its size and weight and staged retraction, the effort required to raise and stow the gear greatly exceeds that required for extension.
The main gear retraction/extension is controlled by the center hydraulic system. It is apparent that the hydraulics failed when the engines shut down after breaking the down-locks and leaving the Main Landing gear bogeys in the tilt position, ready for a next step internal stowage and door closure (that was now never to happen). It is therefore apparent that the dual engine failure and consequent automated RAT extension was precipitated by this gear selection or retraction cycle and thus likely to be either WoW micro-switch or 5G Radar altimeter-effect associated. Due to accumulator depletion, the electric pump load would have spiked to replenish it. This may have precipitated the dual engine shutdown due to an unfiltered electrical surge affecting the Ground/Air microswitches (or a local 5G transmission affecting the RADALT) and resetting the TCMA. The RADALT? Another plausibility? Because of the furore over a spasticated frequency allocation by the US FCC, the US FAA had finally “bought in” and declared that individual nations and their airline operators were responsible for their own 5G frequency spectrum allocations and for taking essential steps to ensure mitigation of the interference effects upon aircraft automated landings and other critical systems caused by their own national approved 5G spectrum decisions. It was admittedly a situation calling for extensive modifications to (and shielding for) the three radar altimeters fitted for redundancy considerations to all modern airliners... for Category 3 ILS approach and landing in zero/zero visibility conditions. The RADALT also features in many air-ground sensing applications. (eg the 747-8). This was an unusual FAA “passing of the buck” to manufacturers such as Honeywell etc. (to sort out with client operators). But then again, it was not the US FCC’s right to dictate the specific 5G frequencies internationally. These spectrum allocations now vary over the wide selection of 5G phones available (and also nationally). 5G Radar Altimeters constitute a part of the ground/Air sensing that changes the TCMA from ground mode (able to fuel-chop engines) to the air mode (inhibited from doing so)... Ground activation is acceptable ...where fuel chopping of uncommanded thrust can prevent runway sideways excursions or runway length overruns. The question now becomes: “Is it more (or less) safe having an automated fuel-chopping capability on BOTH your left and right, rather than leaving it to the pilot to react via his center console fuel cut-off switches... in the unlikely event of a runaway engine after landing (or during an abandoned take-off)? 5G Frequency Variations The frequencies of 5G phones vary nationally based on the frequency bands allocated and used by different carriers in each country. In the United States, for example, carriers such as AT&T, Verizon, T-Mobile, and others use a combination of low-band, mid-band, and high-band 5G frequencies. Low-band 5G frequencies typically range from 600 MHz to 1 GHz, mid-band 5G frequencies range from 1.7 GHz to 2.5 GHz, and high-band 5G (mmWave) frequencies start at 24 GHz and go up to 40 GHz . These frequencies are allocated by regulatory bodies such as the Federal Communications Commission (FCC) and can vary between countries based on spectrum availability and regulatory decisions. In other countries, the specific frequency bands used for 5G may differ, leading to variations in the frequencies supported by 5G phones. Additionally, the deployment of 5G networks can also influence the frequencies used, with some countries focusing more on sub-6 GHz bands while others prioritize mmWave technology. 5G interference? It may be an avenue worth exploring? |
Capn Bloggs
June 19, 2025, 01:40:00 GMT permalink Post: 11905665 |
Originally Posted by
Sycamore
As an ex-tp, I would consider those cut-off switches a danger, and they should have guards either side of each.
Shirtsleeves/watches etc. can get caught, lift switch. Very poor design. Would not pass `military-muster.` Ours: ![]() 787: ![]() |
Capn Bloggs
June 19, 2025, 10:22:00 GMT permalink Post: 11905892 |
Originally Posted by
DTA
That failure can be the result of physical damage or wear so that the knob is stuck in the pulled position. It would not be obvious if you did not look closely.
![]() |
Kraftstoffvondesibel
June 19, 2025, 12:16:00 GMT permalink Post: 11905976 |
Switches fail sometimes. I have changed lots of lots of malfunctioning toggle switches in my day. But both at the same time? It has to be a common thing happening at the same time. Someone slipping both switches into a worn middle detent is such a thing though, that is one habit that could be developed. A slight bump at takeoff and they both go to cutoff. Or they are worn and theres an iphone behind the throttles, as someone mentioned. The switches themselves are on-on 4 pole toggles, and doesn\x92t fail into one position over the other, and gravity would prefer the cutoff position in this design. I mentioned I have used my share of switches, knobs and buttons. In much larger quantities than what you find in aircraft, but without the life and death factor, and thus no SOP. Unexpected things happen, no one dies, but I myself brodcasted jolly sounding very inappropriate intro music over a very dark news report on the unravelling Joseph Frietzl case by dropping my phone on a switch. Several million viewers, a good chunk of which called to complain. Grave errors can be banal. Other than that, common connectors, the harness itself, I have seen a large amount of unexpected electronic things happen when those get bendt the wrong way. Last edited by Kraftstoffvondesibel; 19th June 2025 at 12:30 . |
Seamless
June 19, 2025, 12:27:00 GMT permalink Post: 11905984 |
The spec sheet says 100,000 cycles.
Switches fail sometimes. I have changed lots of lots of malfunctioning toggle switches in my day. But both at the same time? It has to be a common thing happening at the same time. Someone slipping both switches into a worn middle detent is such a thing though, that is one habit that could be developed. A slight bump at takeoff and they both go to cutoff. The switches themselves are on-on 4 pole toggles, and doesn\x92t fail into one position over the other, and gravity would prefer the cutoff position in this design. |
Capn Bloggs
June 19, 2025, 12:29:00 GMT permalink Post: 11905985 |
Originally Posted by
syseng68k
Have a few of that type here
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