Posts by user "Someone Somewhere" [Posts: 63 Total up-votes: 0 Pages: 4]

Someone Somewhere
July 01, 2025, 10:19:00 GMT
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Post: 11914164
Originally Posted by adfad
We know (from the 248-day bug) that full AC power failure is possible and we see from the RAT and landing gear orientation that full AC power failure was likely within ~10 seconds of leaving the ground.
I believe that particular bug is fixed, though it's always possible there's other issues causing a total AC loss.

Not really relevant to what you quoted though, as the scenario in question requires:
  • Engines running on centre tank fuel during takeoff while the aircraft is operating normally
    • We don't know for certain if this is the case. It seems to be but it's not something that happens on other families.
  • Then, total AC failure stopping fuel boost pumps.
  • Engines suction feed from contaminated/full-of-water wing tanks.

I also don't see any evidence that engine driven fuel pumps alone must be able to handle this scenario: provide enough fuel flow for takeoff and climb, even while the pitch is rotating, even in a hot environment with significant weight, even while the gear is stuck down.

I know that the engine driven pumps have documented limitations and that the regulations allow for some limitations. I know that at least one of these limitation is high altitude and I _suspect_ that the design intends for this unlikely scenario (engine driven fuel pumps alone with no AC pumps) to guarantee enough fuel flow to get to an airport and land. I also suspect that the APU is expected to solve loss of all AC generators - and as we know, there wasn't enough time for it to start in this scenario.

The aircraft has two engines and should be able to climb out on one, plus it dropped like a rock . 'Significantly degraded' thrust isn't really compatible with what we saw. You'd also expect the engines to recover pretty quickly as it leveled off.

The limitations at high altitude are primarily air/volatiles degassing out of the fuel. That's not going to be much of an issue at sea level, even if the engines are a bit higher up during rotation.
APU is a nice-to-have; it's on the MEL. If you lose all four generators, it's because of some major carnage in the electrical software/hardware and chances of putting the APU on line even if it's operating are very slim.




Subjects (links are to this post in the relevant subject page so that this post can be seen in context): APU  Centre Tank  Fuel (All)  Generators/Alternators  MEL  RAT (All)  RAT (Deployment)

Someone Somewhere
July 01, 2025, 10:42:00 GMT
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Post: 11914172
Originally Posted by AirScotia
One of the things I've learned on this thread is that planes landing with the RAT deployed may be rare, but it does happen. The videos I've watched suggest that the engines were usually running as the plane landed, but of course the RAT can't be un-deployed in flight.

My question is: what caused the RAT to deploy on those flights? Presumably reports have to be submitted in those cases?
Many are maintenance or production test flights. Someone commented upthread that every Boeing widebody built gets the RAT deployed on its first flight, and I imagine some maintenance procedures require it too.

ASN has a section on electrical power incidents: https://asn.flightsafety.org/asndb/cat/ACSE

In particular try these:

https://assets.publishing.service.go...009_G-EZAC.pdf
https://asn.flightsafety.org/wikibase/233343
https://asn.flightsafety.org/wikibase/219748
https://asn.flightsafety.org/wikibase/34357

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): RAT (All)  RAT (Deployment)

Someone Somewhere
July 01, 2025, 12:59:00 GMT
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Post: 11914257
Originally Posted by Sailvi767
On the 767, 757 and A330 anytime you are in single generator operations the aircraft is load shedding. The 787 with a totally different electrical system might function differently.
The manuals suggest the 787 has even more advanced load inhibition/load shedding, shedding/recovering individual loads as required for both operational and availability reasons.

Remember the 787 uses electrics for engine start, wing anti-ice, centre hydraulics, and cabin air compressors. There's some big electrical loads.

Centre tank boost pumps are probably comparatively small, but if you can conclusively say x is not required during ground engine start , why power it?

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Centre Tank  Fuel (All)  Generators/Alternators

Someone Somewhere
July 01, 2025, 13:08:00 GMT
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Post: 11914265
Originally Posted by adfad
As an electronics and software engineer who has read the AD and related materials on the 248 day bug my understanding is that:
  1. The specific 248-day integer overflow was patched, and before the fix was rolled out, the AD required this system to by power cycled every 120 days to prevent overflow
  2. The PCU software still has the functional requirement to be able to command all AC GCUs to enter failsafe mode, this means that while the initial bug was fixed, the ability for this particular software system to command the same result is still a functional part of the architecture - presumably for safety management of the AC system
  3. This was not the first or last "software overflow error" issue in Boeing or even in the 787
Although I'm not qualified in aviation engineering I do believe from an engineering safety standpoint that this architecture creates a rare but entirely feasible scenario in which the aircraft would be without AC power for at least 30 seconds until the APU could restore it.
Similar failures have happened on 737s/A320s/A330s and others. I'm not denying it's possible. There's a reason it's a certification requirement for the engines not to be dependent on aircraft power. The APU is MELable and battery starts are not extremely reliable.

I do agree that the engine driven pumps should be able to provide fuel alone, the whole point of these pumps is to keep the plane flying within some limitations, high altitude is one of those limitations, I propose that there may be others based on the following:
  • Some more knowledgable people here have proposed or countered vapour lock, fuel contamination and automatic fuel cut-off theories to various degrees - even if these are not enough on their own, loss of electrical during rotation at high temperature could combine with these in a way we have not yet considered
  • Thrust is nonlinear, and while I'm not qualified to say how much loss of fuel flow or loss of thrust would be critical in this scenario we do know that it was a hot takeoff with significant weight and gear remaining down - I know others here have run sims but I don't think anyone has focused on specific thrust / fuel flow params
  • While electric fuel pumps might not be physically necessary for takeoff, my final point is: why are they required for takeoff? Is it not to mitigate cavitation, fuel sloshing at rotation, or any other kind of problem that might be relevant here?
Thrust is non-linear and complex. Reaction engines (i.e. fans, props) are generally most efficient at minimum power - lowest excess velocity. Turbine engines are generally most efficient at high power. These cancel out somewhere in the middle. With two engines at low power, you also don't have the drag from the dead engine or the drag from the rudder countering yaw.

Cavitating destroys pumps rapidly - someone upthread said replacing the fuel pump immediately is SOP if it has suction fed. Expect end of life in tens of hours rather than tens of thousands.

Some aircraft have switched to using jet/venturi pumps powered by returned fuel, like the A220. The electric boost pumps there are mainly for redundancy and are shut down in cruise; only one in each wing tank. Some A320s replace the centre override pumps with venturi transfer pumps.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): APU  Air Worthiness Directives  Fuel (All)  Fuel Cutoff  Fuel Cutoff Switches

Someone Somewhere
July 09, 2025, 18:06:00 GMT
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Post: 11918557
Originally Posted by Propellerhead
Fuel control switches will cut off the fuel at any thrust or thrust lever setting - they need to be able to deal with an uncommanded thrust increase from an engine fault.
The fire switches potentially provide that capability.

There are many types where the shutoff position is a fully aft thrust lever, past a lift-up gate. Apparently this has caused a few human-factors issues because other types use the exact same mechanism for setting reverse thrust.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All)  Fuel Cutoff Switches

Someone Somewhere
July 12, 2025, 00:21:00 GMT
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Post: 11920035
Originally Posted by RiSq
I’ll hold judgement till the report is out as stranger things have happened. But what a seismic shift we have seen in the last 30 years.

30 years ago you worried about flying with certain airlines due to their maintenance records and ages of their fleets.

We are now in the time of choosing your airline of choice by having to research their flight routes over questionable airspace or their training schemes of their pilots.


It is rather worrying that the majority of major airline crashes in the last 20 years have been due to the two fleshy ones riding up front, if not questionable flight planning, Military or terrorist input.

I expect thats going to be about as popular as an lead balloon here.

In fact, I cannot remember the last major mechanical failure that led to a mass loss of life.

The Jeju one is still to be determined, but not sure if that can even be counted due to bird strikes.
I am not sure exactly where to go looking for the data, but bear in mind that total accident rates have also decreased dramatically while flight volumes have increased.

It wouldn't surprise me if solely crew-caused accidents are decreasing slightly, while mechanical/maintenance/technical failures leading to accidents have massively decreased. Crew/dispatch errors hence look far worse in comparison.

Subjects: None

Someone Somewhere
July 12, 2025, 01:00:00 GMT
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Post: 11920049
Originally Posted by Pilot DAR
If I recall correctly, the Mayday call was wording to the effect "thrust not achieved". That sounds like a phrase which could be expected from a pilot who had just frantically tried to restart an engine, and realized that it was not a success, and there would not be an opportunity for another attempt. The pilot aviated, (forget navigation), then communicated - over a period of 13 seconds.
I believe the 'thrust not achieved' was that one made up by a journalist - happy to be corrected.

The EGT was observed to be rising for both engines indicating relight. Engine 1’s core
deceleration stopped, reversed and started to progress to recovery. Engine 2 was able to
relight but could not arrest core speed deceleration and re-introduced fuel repeatedly to
increase core speed acceleration and recovery. The EAFR recording stopped at 08:09:11
UTC
At about 08:09:05 UTC, one of the pilots transmitted “ MAYDAY MAYDAY MAYDAY ”. The
ATCO enquired about the call sign. ATCO did not get any response but observed the aircraft
crashing outside the airport boundary and activated the emergency response.
Sounds like #1 was restarting successfully but they just didn't have enough time for it to get back to high thrust.

#2 may or may not have eventually started successfully; the extra two seconds of no fuel meant it would be a much harder start for the FADEC.

It doesn't sound like the crew have any input on the relight process; if the switch is on, the FADECs will try anything they can to get the engines lit and accelerating ASAP. Repeatedly switching between off and on will not help this process and there are basically no other controls the crew have, especially with no other power to run the engine starters.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): EAFR  FADEC  MAYDAY  Relight

Someone Somewhere
July 12, 2025, 01:47:00 GMT
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Post: 11920083
Spoiler
 
Originally Posted by Finalveridict
It seems like people are jumping to conclusions about the pilots and letting Boeing off the hook without proper investigation. Instead of providing a professional, detailed transcript of the cockpit voice recorder (CVR), we’re just getting casual comments about what the pilot allegedly said. Critical information—like the timing of transmissions, the checklist items completed before takeoff, and other key details that should be on the CVR—are essential for understanding what happened in the cockpit, especially since the crash occurred so soon after takeoff. In my view, the preliminary report feels too convenient for certain parties involved.
This is a preliminary report. It is quite detailed for a preliminary report.

Examining the before-takeoff checklists seems like it would be akin to examining the re-arrangement of the deckchairs before the titanic even hit the iceberg.

The engines were switched off. Unlike Embraer, B & A have no protections stopping you switching an engine off inadvertently. From everything in the report, everything operated exactly as designed. I am not certain of how long the relight window is without windmilling speed, but +- 10 seconds seems entirely reasonable.

The outstanding question that presumably requires much more in-depth investigation of the wreckage items and CVR audio is whether:
  • the cutoff switches were operated deliberately (and by who)
  • the cutoff switches were operated inadvertently (and by who)
  • the cutoff switches were bumped (by what) and the guards failed or weren't installed
  • some electrical failure perfectly mimicked both many-pole switches being operated, then being operated again (seems unlikely)

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): AAIB (All)  CVR  EAFR  Electrical Failure  Fuel (All)  Fuel Cutoff  Fuel Cutoff Switches  Preliminary Report  RUN/CUTOFF  Relight  Switch Guards  Timeline (Preliminary Report)

Someone Somewhere
July 12, 2025, 02:02:00 GMT
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Post: 11920093
Consider this post with a picture of the switches in question:


They must be lifted over the detent (if installed correctly) in each direction.

Originally Posted by LTC8K6
Double pole switches. Pretty simple.You'd have to short (or open) both sets of contacts simultaneously.

One set of poles is for the circuit power, and one set is for the switch position data.
Far more than double pole - I think it's 4-8 ish. See the number of wires in the above picture. A previous post in one of the earlier thread indicated that it was essentially one pole per function - HPSOV, LPSOV, FADEC signal, generator etc. I'm not sure which one the EAFR reads. If it was a single contact failure, you would expect to see disagreement between the various systems controlled by the switch. I think that's very unlikely given both 'failed' in the same way near simultaneously and 'recovered' when switched.

For reference, it's pretty common for industrial emergency stop buttons to have 2-3 poles: redundant poles for the actual fault switching (legislative requirement above certain hazard levels), plus an additional pole for monitoring.

Originally Posted by LTC8K6
Wouldn't they already know if the detents were missing in this case? They recovered the switches and told us what position they were in at impact.
Depends on when they identified the SB and how obvious the lack of or incorrect fitting of detents is.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): EAFR  FADEC  Fuel (All)  Fuel Cutoff Switches  Fuel Cutoff Switches (detent)  Generators/Alternators  High Pressure Shutoff Valve

Someone Somewhere
July 12, 2025, 02:34:00 GMT
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Post: 11920108
Originally Posted by Xeptu
Regardless of how this happened I find it perplexing that a switch with such consequence in either position can be operated with a flick of the wrist.
Firewall shutoff switches are guarded, fire bottle switches are guarded or require both hands to operate, all require two deliberate actions to operate, except two switches in the middle of the console which do so many consrquential things..
They have a reasonably substantial pull-out gate.

Over-guarding stuff can have its own issues. People become used to operating the guard as part of normal operations, and it becomes muscle memory.

Apparently Embraer aircraft inhibit the shutoff switch if the thrust lever is above idle - if you have a stuck thrust lever, you need to use the fire shutoff.

Another option would be to have a blocking solenoid (with override button) similar to the landing gear lever while airborne or at high speed.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Gear Lever  Muscle Memory  Switch Guards

Someone Somewhere
July 12, 2025, 11:02:00 GMT
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Post: 11920495
Originally Posted by Natterjak
The accident aircraft was written up for a status message of ”STAB POS XDCR” on the previous flight, which is a message relating to implausible data from the stab trim switches. It was released from maintenance (according to the preliminary report) at 06:40UTC ahead of an 07:40UTC departure (the crash flight) with ”no fault found”.

On the 787-8, as all modern planes, switches are not cabled as dry closing contacts all the way from the switch poles to the affected end devices (FADECs in the case of fuel cutoff switches), but rather connect locally to an analogue/digital converter to encode the switch position data onto the digital comms bus ARINC629 which allows all aircraft systems to talk to one another.

Are the fuel cutoff switches, which are positioned adjacent to the stab trim switches, connected to the same ADC module which produced the error message on the previous flight, which maintenance was unable to resolve before the accident flight took off? I do not know, but it must be worthy of being looked into.
I believe the fuel cutoff switches are one of the exceptions to this. They are direct wired. Stab trim may well be too.

I think they're called remote data concentrators - in many cases it is a conversion from a direct digital input to a bus signal; electronics would not call it an 'analog' input unless it was actually measuring a quantitative value.

Originally Posted by Musician
Was the RAT deployed manually?
The report says,
As per the EAFR data both engines N2 values passed below minimum idle speed, and the RAT hydraulic pump began supplying hydraulic power at about 08:08:47 UTC.
This was 5 seconds after the fuel was cut off.

It suggests to me that the RAT deployment was initiated while the engines were still above idle and generating electrical power. Obviously one of the pilots could have done it via depressing the switch, as it's a "dual engine failure/stall" memory item (see Air India Ahmedabad accident 12th June 2025 Part 2 ) that won't hurt anything.

Is there a way for the RAT to deploy while the engines are still above idle?
I think I have seen a previous reference that the generators are disconnected when you select the switches to cutoff (or very shortly afterwards), not when the engine actually drops below idle. That could account for a few seconds of spool down time.

Originally Posted by AfricanSkies
What is unusual to me is the 4 second gap between moving Eng 1 fuel switch from cutoff to run, and moving Eng 2 fuel switch from cutoff to run.
One would imagine that in this situation, speed of response would have been critical.
That is a very good question IMHO.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): EAFR  Fuel (All)  Fuel Cutoff  Fuel Cutoff Switches  Generators/Alternators  Hydraulic Failure (All)  Preliminary Report  RAT (All)  RAT (Deployment)

Someone Somewhere
July 12, 2025, 11:22:00 GMT
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Post: 11920523
Originally Posted by Uplinker
This crossed my mind too. This is called an "action-slip" by designers: a valid and frequently practised action being applied to entirely the wrong situation, resulting in an (extremely) invalid action.

On this flight, the relative drop in noise and calm that follows the landing gear doors closing after the gear retracts during the initial climb, might have caused an action slip by PIC to perform the engine shut-down procedure used when parking on stand.

Unlikely though, I would hope.
The gear were never retracted on this flight, so the action being caused by gear up quietness is not feasible.

Action slip in general... technically possible, but there should still be no actions being taken other than gear up (and probably still a bit early for that).

Engines off instead of gear up is one hell of an action slip.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Action slip  Engine Failure (All)  Engine Shutdown

Someone Somewhere
July 13, 2025, 04:27:00 GMT
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Post: 11921012
Originally Posted by LTC8K6
There are good explanations and diagrams of the switches in the thread.

With that info, your scenario seems very unlikely.
Originally Posted by icarus sun
Anyone have a wiring diagram of the run/cutoff switch and a diagram of the wiring underneath the switches.
Does the data recorders record the actual,position of the switches or the electrical output of the switches
Industrial electrician here.

I have only seen a diagram for I think the 737. I remember there being a listing of what each pole did, but I can no longer find the post.

My expectation/speculation, though, is this:

The EAFR gets its information on cutoff switch position from the FADECs via data buses, similar to almost all other engine data. We have N2 information in the report after the engines were switched off, so clearly there are no concerns about this data not being captured.
This means that the FADEC's data of where the switches are is almost certainly the EAFR's data.

There are other poles on the switches that do other things - I think it was opening/closing the LPSOV and enabling the generators. The fourth pole in the 'cutoff' position was IIRC not used because the generators don't get a disable signal, whereas the LPSOVs are powered open in the run position and powered closed in the cutoff position.

If the switches were physically operated and in good electromechanical condition (not counting the possibly faulty gates), we would expect all four poles to operate essentially simultaneously, with the four 'run' contacts opening and the four 'cutoff' contacts closing. Not only would the EAFR pick up that the FADECs were commanded off, but also that the LPSOV closes after a short delay, and the generators drop offline before N2 drops below idle.

When the switches are moved back to run, we would likewise see the position of each LPSOV return to open.

(this does not necessarily mean that a person intentionally operated them, but that the lever actually moved).

If there was a wiring fault, contamination, or internal switch failure, we would probably not see this. Instead, you might see the LPSOV remain open despite the engine shutting down, or perhaps the FADECs trying to keep the engine running while the LPSOV has closed and shut off fuel, or the two FADEC channels receiving different run/cutoff signals - and all of this would probably happen differently on each engine (if it affected both engines at all). There is no indication of this in the report.

These are not your basic light switch where the load is either powered or not powered. They're four switches ganged together and operated in unison, and each channel powers either thing A or thing B. If you have both or neither A & B powered (for longer than the ~50ms that the switch takes to move between positions), this is a fault that should be visible in the EAFR data in some/many cases. Think valves being displayed in orange as 'position unknown'.

If all run contacts opened, and all cutoff contacts closed, the switch moved from run to cutoff .

I don't know whether they analysed the EAFR data in this much detail yet, but coupled with a potential click sound on the CVR, I think there's going to be very very little doubt at the end of the investigation whether the switches physically moved or not, and I strongly expect they did.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): CVR  EAFR  FADEC  Fuel (All)  Fuel Cutoff Switches  Generators/Alternators

Someone Somewhere
July 13, 2025, 05:47:00 GMT
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Post: 11921037
Originally Posted by Mr Optimistic
I suppose this event will be a setback for any ambition for single pilot operation.
There's a reasonably substantial thread touching on that here: I'm starting to think automation may be the answer

My take is that removing the authority to crash the plane is something that's necessary for single pilot operations. That means crew can't disable both engines, or all generators, or all transponders (MH370), or put the plane into unrecoverable situations. That's a very very short summary.

Incidents like this (potentially) imply that it may be necessary for two-pilot operations too.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Generators/Alternators

Someone Somewhere
July 13, 2025, 07:39:00 GMT
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Post: 11921091
Originally Posted by DTA
An answer to this is just a few posts back. Each switch has 4 sections which control different functions. It is not a single switch with software behind it. Multiple simultaneous separate failures would be needed if the switch itself did not move.
We don't have definitive data on this AFAIK . There's some level of speculation and guesswork.

Either shutting fuel valves or commanding the FADECs off will shut down the engines - the redundancy is not in the desired direction here.

Subjects: None

Someone Somewhere
July 13, 2025, 08:31:00 GMT
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Post: 11921131
Originally Posted by Bunk-Rest
I was thinking last night, that the only time I have ever seen both fuel control cutoffs operated together, has been in the simulator.
If a crew is getting in the sim to do an exercise or practice. To save time, whilst the pilots are getting in the seats, the instructor is getting the sim ready, ie getting the door shut, the machine upon it\x92s jacks etc. often to save a lot of startup time, he will lean over the console, move both switches to the \x93running\x94 position, tben press the master reset at the back, snd hey presto the aircraft is at the start of the runway, all engines running, ready to go!
Simples. - saves 10 minutes of sim time.
Not when shutting down engines after arriving at the gate?

As SLF, a 1-2 second gap between engines shutting down seems pretty typical, assuming no single-engine taxi. To the point where switching both off at once could easily be a single learnt routine.

Subjects: None

Someone Somewhere
July 13, 2025, 09:02:00 GMT
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Post: 11921159
Originally Posted by rigoschris
It\x92s not great that they mention the SAIB in the Preliminary Report but don\x92t give any details to the state of the particular switches of this airplane.

The metal parts of the switches seem intact in the picture, so it would be easy to check if the \x93lobes\x94 in the movable and stationary parts of the switches were there. A close-up picture would lay this topic to rest.

This omission is causing a lot of speculation online.
I suspect they thought that stating the switches had been replaced twice since the bulletin was published would dispel such concerns.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Preliminary Report  Special Airworthiness Information Bulletin

Someone Somewhere
July 13, 2025, 10:32:00 GMT
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Post: 11921213
Originally Posted by Mrshed
Don't think it neccessarily adds anything for me, other than:

- Would we expect ADS-B data to stop on engine transition to run? Note that ADS-B data was received between 08:08:43 and 08:08:51, so apparently only received in the time window that the switches were in "cutoff"
- The window between the switches being shut off and moved to run could be as short as 8 seconds, and the window between engine 1 and engine 2 being moved to run could be as short as 2 seconds
- The statement on the CVR could be a wide range of timepoints.

The ADS-B data is in my view odd, albeit this might be my lack of understanding. Yes, not synchronised, but unless the timestamps are way out (like 10 seconds out, and given the timestamp of max altitude, this feels incredibly unlikely), ADS-B data was transmitted without issue during phase 2 (both engines off, no RAT), and phase 3 (both engines off, RAT)...but NOT phase 4 (both engines firing back up, presumably still with RAT?). Bear in mind that phase 4 is almost half of the short flight. Also it would appear no data during phase 1 (both engines on), including during takeoff, despite receiving data during taxi?
I think in the Jeju thread, it was noted that one of the transponders was on an AC bus and the other was on the standby bus. If they had been using the other transponder (swapped each flight), then we would have had ADS-B for the full flight.

Assuming the 787 is similar, perhaps the aircraft was broadcasting ADS-B for the full flight (with the transponder running off main battery/RAT power) but the reception was marginal, resulting in no reception until just after liftoff and no reception once they start to sink again.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): ADSB  CVR  Fuel (All)  Fuel Cutoff Switches  Preliminary Report  RAT (All)  Timeline (Preliminary Report)

Someone Somewhere
July 14, 2025, 08:01:00 GMT
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Post: 11921930
Originally Posted by tdracer
Engine restart (i.e. "Quick Windmill Relight"): Even if the igniters were firing, at high power they won't actually spark (the electrical resistance or the air at several hundred psi prevents a spark) - so they won't spark until you get down somewhere near idle if you're close to sea level. Once the engine has dropped below the min idle, it takes a long time for it accelerate back to even an idle condition. At takeoff power, the compressor components get very hot - do a power cut the air coming in the compressor gets heated by the residual heat in the compressor. This in turn limits how fast you can add fuel in the burner without excessively back pressuring the compressor and causing a compressor stall. So it actually takes longer for the engine to accel to idle that it would during a normal (cold engine) start. The 5 seconds to 95% accel requirement referenced earlier is from a stable 'high' idle (we typically call it 'approach idle' since it's automatically selected when landing flaps are selected). Approach idle is ~10% N2 higher than the in-flight minimum idle, so that takes several more seconds. Bottom line, after initiating the Quick Windmill Relight, you're not going to have usable thrust for at least 30 seconds - probably closer to 60 seconds..
I have not seen this specifically addressed, so would this same timing be expected if the engine flamed out (e.g. due to extreme rain ingestion) and continuous ignition (not present on the 787, but auto-ignition does the same thing) brought the engine back?

If the restriction to getting the engine relit earlier (well above idle N2) is only the spark gap, I am somewhat surprised that beefier igniters, perhaps with high/low voltage settings (for emergency/normal use), are not used. Compressed air is a reasonable insulator, but it's nowhere the oil, SF6, or vacuum that HV operators use in tight spaces.

Bigger igniters might mean you can spark the fuel at ~70% N2 at which point you're presumably seconds away from having thrust again, and don't do the significant engine damage associated with I assume EGT exceedances from scheduling high fuel to ramp N2 rapidly with already-hot parts.

Originally Posted by Xeptu
My final thoughts for this event.
Misinformation, most of us including myself was of the view that Gear Up had been selected because we saw an image believed to be the accident aircraft with the bogeys stowed for retraction.The report image shows that they were not and the Gear Selector was down. A crucial element in the sequence of events.
I suggested early on that the loss of centre hydraulic pressure caused the gear to return to a 'natural'/neutral tilt. That's looking likely.

Originally Posted by TURIN
I think there is a bit of confusion running in this thread about how the auto restart function works.
Normal start uses a lot of electrical power to drive the two starters. In a situation with only the RAT supplying electrical power there won't be anywhere near enough power to turn even one starter. Restart relies on windmilling only. Igniters don't need a huge amount of power, fuel will be gravity fed to the engine driven pumps. The APU autostart function will use power from the dedicated APU battery only.
Edit to add, it can take an age for the APU to start off the battery. Well over a minute.
They were outside the windmilling envelope (too slow), so with no combustion, the engines were decelerating. There's a narrow window where the engines are still spinning fast enough to light off and re-accelerate (it looks like 2 missed this), but per TDR above, not so fast that they can't be lit.

You can spin up the engines in three ways: starter motor (electric or pneumatic, depending on type), windmill (but at low speeds, the RPM given by a windmill won't be enough), or the inertia of the already spinning engine. Quick relight I believe is predominantly inertia.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): APU  Hydraulic Failure (All)  Quick Windmill Relight  RAT (All)  Relight

Someone Somewhere
July 14, 2025, 08:22:00 GMT
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Post: 11921946
Korea has made CCTV mandatory in operating theatres .

I work in a facility where cameras outnumber staff on site roughly 3:1.

Various forms of public transport (trains, buses, trams, I assume many boats) have ubiquitous external, internal, and in at least some cases driver facing CCTV.

Plant control rooms (including power stations, dams, and chemical facilities) have ubiquitous CCTV.

Driver-facing cameras with alerting and KPIs for events like speeding, hard braking, phone usage/distracted driving, and fatigue detection are becoming increasingly common for fleet vehicles, thanks largely to hefty insurer discounts. That's not just heavy trucks but things like HVAC installers, linemen, and ambulances.

I suspect anyone who thinks this will never happen in aviation is being rather optimistic.

Originally Posted by bulldog89
The issue is you don't know how FDR data is used.
And, no, it's not just in case of abnormal occurrences.
CVR is likely what was meant.



Subjects (links are to this post in the relevant subject page so that this post can be seen in context): CCTV  CVR  FDR