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Someone Somewhere
2025-06-12T12:34:00 permalink Post: 11899162 |
For an aircraft that will likely have TOGA pressed and be at a high power setting (plus the RAT deployed) it sounds awfully quiet.
Perhaps the gear was down because they knew they were going to force land due to lack of thrust. (Only a 738 driver), but the electric pumps to drive the hydraulics is much slower than the engine driven pumps and so flap selection / re-selection could be not as expected. RIP to all involved. The 787 has 2x Enhanced Airborne Flight Recorders (EAFR), which each record both cockpit voice and flight data. Hopefully flight data is not going to be an issue for this investigation. It's also maybe visible in a few stills (e.g. post 64). Last edited by Someone Somewhere; 14th Jun 2025 at 06:01 . 2 users liked this post. |
EEngr
2025-06-12T16:15:00 permalink Post: 11899421 |
Two 225kVA generators per engine (plus two on the APU). Directly driven with no constant speed drives so they are variable frequency. That is converted to high voltage DC and distributed around the plane. So, four or six independant sources.
Several load distribution centers, where the DC is supplied to various loads and in some cases converted to 28Vdc, 400Hz AC, or other levels as required by the loads. The switching between alternate sources would depend on each load buses criticality. There are also those lithium ion standby/starting batteries available. So, theoretically very redundant. But highly complex systems also suffer from the possibility of hidden faults which may escape certification testing and analysis. We'll see. 8 users liked this post. |
bobdxb
2025-06-12T17:23:00 permalink Post: 11899506 |
2 users liked this post. |
ahmetdouas
2025-06-12T18:09:00 permalink Post: 11899555 |
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TURIN
2025-06-12T18:22:00 permalink Post: 11899571 |
Each engine has two identical Variable Frequency Starter Motor Generators. They are a combined starter motor and generator. More in this ancient thread here- 787 electrical system - variable frequency generators? 4 users liked this post. |
BrogulT
2025-06-12T20:41:00 permalink Post: 11899711 |
Without getting into how an MEL actually works, here's an excerpt from an actual 787 MEL.
![]() AGCU = APU Generator Control Unit, VFSG = Variable Frequency Starter Generator. IDK what exactly the AGCU does nor why the left one is important. |
IFMU
2025-06-12T21:25:00 permalink Post: 11899752 |
There are no IDGs on a 787. There are 4 identical variable frequency starter-generators.
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tdracer
2025-06-12T23:19:00 permalink Post: 11899828 |
1) Fuel 2) Thrust lever position Everything else is 'goodness'. The FADEC has its own dedicated (gearbox mounted) electrical generator (actually alternator), so even a 100% aircraft power loss wouldn't affect the FADECs ability to control the engine. It was right at takeoff - 'suction feed' would be more than sufficient if the aircraft fuel pumps failed, FMC and other aircraft inputs have only a secondary effect on the thrust setting, it's primarily determined the thrust lever position. So there is no known way that a fault in the engine/aircraft interface could cause a large loss of thrust. 3 users liked this post. |
Alty7x7
2025-06-13T03:42:00 permalink Post: 11899963 |
About the only way that could happen would be some catastrophic software 'hole' in the GEnx-1B FADEC software. By design, the only thing the engine control really needs to adequately the engine is:
1) Fuel 2) Thrust lever position Everything else is 'goodness'. The FADEC has its own dedicated (gearbox mounted) electrical generator (actually alternator), so even a 100% aircraft power loss wouldn't affect the FADECs ability to control the engine. It was right at takeoff - 'suction feed' would be more than sufficient if the aircraft fuel pumps failed, FMC and other aircraft inputs have only a secondary effect on the thrust setting, it's primarily determined the thrust lever position. So there is no known way that a fault in the engine/aircraft interface could cause a large loss of thrust. |
aeo
2025-06-13T06:43:00 permalink Post: 11900069 |
You are quite correct. Every wide body Boeing (and Airbus) twin plus the 747-8 has a RAT - Some drive a generator and/or some drive a hydraulic pump. The reason for the 748 having a RAT is that for a 3 or more engine flameout (Boeing speak for a 4 engine flameout) the EDP’s are depressurised to unload the gearbox for ease of windmilling. Hence, no engines = no hydraulics. Edited to clarify the different reasons for the RAT. Edited to add every “wide body”
Last edited by aeo; 13th Jun 2025 at 08:04 . |
Someone Somewhere
2025-06-13T08:06:00 permalink Post: 11900136 |
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Gin Jockey
2025-06-13T08:09:00 permalink Post: 11900142 |
What the 767s I flew did have, was a hydraulic generator (or 2 in some cases), but that sure ain\x92t a RAT. |
violator
2025-06-13T10:00:00 permalink Post: 11900272 |
About the only way that could happen would be some catastrophic software 'hole' in the GEnx-1B FADEC software. By design, the only thing the engine control really needs to adequately the engine is:
1) Fuel 2) Thrust lever position Everything else is 'goodness'. The FADEC has its own dedicated (gearbox mounted) electrical generator (actually alternator), so even a 100% aircraft power loss wouldn't affect the FADECs ability to control the engine. It was right at takeoff - 'suction feed' would be more than sufficient if the aircraft fuel pumps failed, FMC and other aircraft inputs have only a secondary effect on the thrust setting, it's primarily determined the thrust lever position. So there is no known way that a fault in the engine/aircraft interface could cause a large loss of thrust. 1 user liked this post. |
babybaby
2025-06-13T10:29:00 permalink Post: 11900315 |
FR24 data appears to stop shortly after airborne but well before impact.
That would seem to align with the significant loss of electrics as a result of loss of engine generators theory? Flaps prematurely retracted shouldn\x92t be a cause of loss of electrical power to the transponder. If electrical power was normal then one would have expected data info until impact, regardless of flap position. 7 users liked this post. |
DTA
2025-06-13T10:42:00 permalink Post: 11900329 |
Reading the various reports about electrical problems on the prior and this flight, such as flickering lights reminded me of the BMI A321 incident discussed here 15 years ago:
https://www.pprune.org/archive/index.php/t-433616.html A faulty generator caused all sorts of problems with control of the aircraft. It is a reminder that complete electrical failure is not the only failure mode. Shutting down the faulty generator on that aircraft recovered the situation, but they had time and altitude on their side. |
ZeBedie
2025-06-13T10:55:00 permalink Post: 11900342 |
One thing which could cause simultaneous unexpected idle power is the autothrottle. I'm thinking about this, leading to a crew too startled to retract the gear and too distracted to push the thrust levers forward, as a possible cause. As others have said, the RAT could have been manually deployed - an action which would make sense to pilot convinced that he was about to lose both engine driven generators.
2 users liked this post. |
Semreh
2025-06-13T11:17:00 permalink Post: 11900372 |
The Dreamliner as two identical \x93Enhanced Airborne Flight Recorders\x94, one in the tail section and one beneath the flight deck. Each one contains the CVR + FDR in one module, both have 10 minutes of battery power backup. I see reports that the one in the tail section has been recovered.
The concept of powering 'critical (sensor) equipment' has been floated - the problem being that it must be possible to power down malfunctioning equipment in case of fire - real or suspected. Having independent power supplies and battery back-ups all around the airframe, each with an ability to lose their magic smoke, is a poor idea. Commercial passenger jet aircraft already have robust power supplies with multiple generators and emergency battery support. However, if one malfunctions, rather than fails completely, it can be difficult to decide which one to disable, as it can cause problems in all systems. |
Someone Somewhere
2025-06-13T11:34:00 permalink Post: 11900389 |
It's fine that the \x93Enhanced Airborne Flight Recorders\x94 have 10 minutes battery backup. If the bits of equipment/sensors sending data to be recorded don't have power, you will be recording 10 minutes of silence/blank data.
The concept of powering 'critical (sensor) equipment' has been floated - the problem being that it must be possible to power down malfunctioning equipment in case of fire - real or suspected. Having independent power supplies and battery back-ups all around the airframe, each with an ability to lose their magic smoke, is a poor idea. Commercial passenger jet aircraft already have robust power supplies with multiple generators and emergency battery support. However, if one malfunctions, rather than fails completely, it can be difficult to decide which one to disable, as it can cause problems in all systems. Once the RAT deployed at least some data should have come back.
Now, I am probably wrong about this, but if you forget to set the altitude window to the first altitude in departure and leave it at 0 (which with some airlines the previous crew will do on shutdown) the following might possibly occur. At 50 feet LNAV engages, at 100 feet the autopilot engages, at 400 feet VNAV engages but as the altitude window is set to 0 the aircraft (on autopilot) now descends to capture 0 feet. The speed at this point in VNAV is low (max V2 + 20 kts) so, to maintain that, both thrust levers close. This, of course, would be totally unexpected and could have a startle effect. If you do not realise what has caused this you might think that there is a problem with the engines and you have very little time to deal with it. I would suggest that putting out a Mayday call at this stage is not a good use of time.
As I stated at the beginning this is probably very unlikely and may not be possible, but could be tried in a simulator. It does not explain the RAT and generally you would expect crews to shove the thrust levers fully forward. 1 user liked this post. |
Xeptu
2025-06-13T11:53:00 permalink Post: 11900411 |
Assumptions
30 secs to 100 kts from TO power set.and 200 kts after 60 seconds Impact occurred 30 secs after Vr 1 nm out, so about 120 kts and no more than 300ft The gear was not or could not be retracted. Without doubt the crew knew impact was inevitable at least 10 seconds prior to impact noted by body angle change in video evidence whether a Mayday Call was in fact made or not. I think that the only thing that would matter for any of us in that 20 seconds would be THRUST and everything it's got. Which occurred first, the loss of thrust on both engines causing all generators to go offline or a total electrical failure that caused flight Idle thrust. |
DunlopDanglerUK
2025-06-13T12:01:00 permalink Post: 11900420 |
One thing which could cause simultaneous unexpected idle power is the autothrottle. I'm thinking about this, leading to a crew too startled to retract the gear and too distracted to push the thrust levers forward, as a possible cause. As others have said, the RAT could have been manually deployed - an action which would make sense to pilot convinced that he was about to lose both engine driven generators.
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