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Chiefttp
2025-06-18T00:09:00 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. 3 users liked this post. |
EDLB
2025-06-18T19:15:00 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. 25 users liked this post. |
Nick H.
2025-06-18T21:30:00 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
2025-06-18T21:47:00 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.
6 users liked this post. |
777ret
2025-06-18T22:38:00 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. 3 users liked this post. |
sycamore
2025-06-18T22:49:00 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 Jun 2025 at 23:12 . Reason: Fixed your punctuation. 5 users liked this post. |
OldnGrounded
2025-06-18T23:16:00 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.
6 users liked this post. |
bbofh
2025-06-19T01:30:00 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? 6 users liked this post. |
Capn Bloggs
2025-06-19T01:40:00 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: ![]() 2 users liked this post. |
Seamless
2025-06-19T09:30:00 permalink Post: 11905864 |
https://ad.easa.europa.eu/blob/NM-18...SIB_NM-18-33_1
The FAA recommends that all owners and operators of the affected airplanes incorporate the following actions at the earliest opportunity: 1) Inspect the locking feature of the fuel control switch to ensure its engagement. While the airplane is on the ground, check whether the fuel control switch can be moved between the two positions without lifting up the switch. If the switch can be moved without lifting it up, the locking feature has been disengaged and the switch should be replaced at the earliest opportunity.
Last edited by Senior Pilot; 19th Jun 2025 at 11:13 . Reason: Image 3 users liked this post. |
Capn Bloggs
2025-06-19T10:22:00 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.
![]() 7 users liked this post. |
Seamless
2025-06-19T12:27:00 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. 2 users liked this post. |
Capn Bloggs
2025-06-19T12:29:00 permalink Post: 11905985 |
Originally Posted by
syseng68k
Have a few of that type here
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Lead Balloon
2025-06-19T12:45:00 permalink Post: 11905991 |
The discussion about the fuel control switch design is interesting so far as it goes, but I'm more interested in the physical arrangements under the bracket to which they're fitted and the associated connection and wiring arrangements. No doubt the arrangements are designed so as to reduce to 'vanishingly small' the probabilities of any common shorts to the wrong places, but who knows, for sure, how the switches and connections and wiring were installed in the accident aircraft, or whether there was a piece of swarf or other FOD that ended up somewhere that it should not have been (i.e. anywhere on the aircraft) during manufacture or maintenance.
3 users liked this post. |
Capn Bloggs
2025-06-19T12:55:00 permalink Post: 11906000 |
Originally Posted by
syseng68K
I guess it depends on the model
Not so the Boeing fuel switches: they can be relatively easily "sat" in the middle, on the centre raised bit and could be bumped either way. Hence our (non-787) FCOM saying make sure you jiggle them when you put it in the On position to confirm it's locked there. 5 users liked this post. |
Xeptu
2025-06-19T12:57:00 permalink Post: 11906003 |
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OldnGrounded
2025-06-19T13:06:00 permalink Post: 11906009 |
Mods, feel free to remove this if you think it's not contributing.
Folks, the exchange here about the cutoff switches ("fuel control switches") is exactly the kind of discussion that contributes meaningfully to our collective understanding of one possible causal or contributing factor in the accident. Smart, well-informed people politely considering and evaluating the suggestions of others. No snark or sniping. Love it. 16 users liked this post. |
OldnGrounded
2025-06-19T13:51:00 permalink Post: 11906035 |
And add the radio altimeter(s). I think, but don't know, that they provide inputs to the FADEC TCMA function also. Last edited by T28B; 19th Jun 2025 at 14:38 . Reason: brackets completed 1 user liked this post. |
Seamless
2025-06-19T14:08:00 permalink Post: 11906053 |
I have read most of the thread (old and new). As a lawyer working in forensic investigations, I am constantly involved in problem-solving. My field of work also includes complex investigations related to insolvencies, which almost always require an analysis of the causes behind a specific, established outcome. In doing so, I naturally also have to deal with probabilities. However, it often turns out that the most likely or plausible explanation does not reflect what actually happened.
Many of the considerations I’ve read fail because the simultaneous failure of both engines is extremely unlikely, leading to a constant search for higher-order causes. It was suggested that an incorrect altitude setting led to an early thrust reduction. However, this would not explain the deployment of the RAT (Ram Air Turbine), especially since the thrust could have been readjusted. FADEC and TCAM are highly redundant systems, and TCAM failure is unlikely due to WOW (Weight on Wheels) logic, making a simultaneous engine failure after VR equally improbable. With that said, and with regard to my question concerning the AD that relates to the fuel control switches (FCS), my thought—and it was nothing more than that—was that their activation becomes more probable if it can occur accidentally. That’s how I came across SAIB: NM-18-33. Another user then brought up an iPhone. That notion would, of course, be dramatic—but how unlikely is it really that after approximately 10,000 actuations between December 2013 and June 2025, the two FCS no longer lock perfectly? Considering all of this, I find it quite conceivable that the A/T slightly reduced thrust in the first seconds after VR (e.g., if an incorrect target altitude had been entered) and that an object lying between the thrust levers and the FCS could have pushed the FCS into the “Off” position. Due to the buttons on top of the switches, which provide some resistance, it’s even possible that the object both pulled and pushed them. But all of this is speculation. The investigation report will bring clarity. Even if my theory is not confirmed, I still believe that the positioning and mechanism of the FCS are suboptimal. Switches of such critical importance should be better protected, and movements in the area in front of the switches (like reducing thrust) should not follow the same direction as shutting off the fuel supply. A different switching direction alone would provide more safety—especially considering that the FCS are protected laterally by metal plates. 5 users liked this post. |
Aerospace101
2025-06-19T14:11:00 permalink Post: 11906054 |
It does not follow that MCAS malfunction is a software malfunction.
As far as I know, the software functioned exactly as it was specified/required to function. The problem did not lie in the quality of the software, as you suggest. It lay in the functional requirements for the function, and the hazard analysis of those requirements, and those are manufacturer tasks. In a total electrical failure, when the system switches to emergency battery power, how are input variables like rad alt and wow switches processed? (these were inputs someone mentioned on the 747-8, have the TCMA inputs been identified yet?) I speculate the gear truck forward tilt is a symptom of a C hydraulic failure caused by a total electrical failure around the time of VR. Once they got 10 deg nose up on the rotation, with a total electrical failure, could the FADEC receive erroneous rad alt or wow inputs, and how would TCMA handle these inputs in the transition from ground to air logic? What is baffling is the simultaneous nature of the suspected dual engine shutdown. There is no obvious asymmetry, with the flight path or rudder movements. If the engine fuel control switches had been manually cut one at a time, there should have been some visible flightpath change or flight control response. Something happened to both engines at exactly the same time. 2 users liked this post. |
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