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| barrymung
2025-06-12T16:17:00 permalink Post: 11899426 |
Gear unable to be retracted and flaps retracted due to no hydraulic pressure? It would certainly explain the RAT being deployed and the loss of lift.
1 user liked this post. |
| Speedbird744
2025-06-12T16:18:00 permalink Post: 11899430 |
Of course the RAT will deploy if all three hydraulic systems have low pressure even with both engines running. This is the case on the 77/78. |
| golfyankeesierra
2025-06-12T17:46:00 permalink Post: 11899534 |
• both engines have failed • all three hydraulic system pressures are low • loss of all electrical power to captain’s and first officer’s flight instruments • loss of all four EMPs and faults in the flight control system occur on approach • loss of all four EMPs and an engine fails on takeoff or landing (EMP = electric motor pump, hydraulic) FYI the RAT is an emergency source for electrical and/or hydraulic power. Last edited by golfyankeesierra; 12th Jun 2025 at 17:57 . |
| TURIN
2025-06-12T18:02:00 permalink Post: 11899550 |
As far as I know the flaps will stay where they are if hydraulic power is lost. There is an electrical over ride function as a back up but I doubt the crew would have used that as it's a guarded switch.
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| nachtmusak
2025-06-12T19:29:00 permalink Post: 11899646 |
Question: would the ram air turbine (if truly it was deployed) have been capable of providing hydraulic power at their airspeed & altitude? I'm aware that it loses effectiveness below a certain number of knots, but I'm not sure what that number is for the 787.
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| FlightDetent
2025-06-12T19:38:00 permalink Post: 11899657 |
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| 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 . |
| nachtmusak
2025-06-13T12:20:00 permalink Post: 11900441 |
Related question: I asked earlier at what speed the 787's RAT becomes effective in providing hydraulic power. Is it possible that by the time the RAT deployed, the aircraft had lost airspeed to the point that it would have struggled to produce an adequate amount of pressure? Taking the Gimli Glider incident as an example, my understanding (could be wrong, this was from a magazine article) is that as they bled off speed to land, they ended up short enough of hydraulic power that they started to experience control difficulties, with the plane responding fairly sluggishly. If that's the case and this poor crew was going through something similar, it might explain why they seem to do very little about their situation.
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| aerobat77
2025-06-13T12:44:00 permalink Post: 11900472 |
Question is why both engines lost power . Foreign object ingestion , contaminated fuel or both cutoff levels operated ? We do not know .
Any autothrust discussion is misleading since every pilot in that situation will firewall the levers whatever thrust reduction was selected for TO . the same is true for the RAT discussion- if enough hydraulic pressure was generated or not . The plane pitched up last second so there obviously was control until the end . Of course , without energy pulling alone will not bring you anywhere . Why did both engines fail the same second as they would be cut off ??? |
| Raffael with FF
2025-06-13T12:45:00 permalink Post: 11900474 |
Just my two cents, from the perspective of an aircraft engineer with a background primarily in Airbus. 10 users liked this post. |
| sSquares
2025-06-13T12:48:00 permalink Post: 11900479 |
Question is why both engines lost power . Foreign object ingestion , contaminated fuel or both cutoff levels operated ? We do not know .
Any autothrust discussion is misleading since every pilot in that situation will firewall the levers whatever thrust reduction was selected for TO . the same is true for the RAT discussion- if enough hydraulic pressure was generated or not . The plane pitched up last second so there obviously was control until the end . Of course , without energy pulling alone will not bring you anywhere . Why did both engines fail the same second as they would be cut off ??? The "gear-up" places additional load on the hydraulic pumps and the result of that is step increase of load on the generators. Was this the trigger of the failures? |
| violator
2025-06-13T12:56:00 permalink Post: 11900487 |
Question is why both engines lost power . Foreign object ingestion , contaminated fuel or both cutoff levels operated ? We do not know .
Any autothrust discussion is misleading since every pilot in that situation will firewall the levers whatever thrust reduction was selected for TO . the same is true for the RAT discussion- if enough hydraulic pressure was generated or not . The plane pitched up last second so there obviously was control until the end . Of course , without energy pulling alone will not bring you anywhere . Why did both engines fail the same second as they would be cut off ??? Let\x92s be careful about absolutes. Emirates 521 and Turkish 1951 are both examples of crews not firewalling the thrust levers despite low energy. The late pitch up could be due to the onset of a stall not an order from the crew. TCMA is function which can reduce thrust on both engines simultaneously. It had done so in error in the past resulting in an AD. It uses air/ground logic so that it only operates on the ground, however note that at the point of thrust loss the gear is still down without any movement of the gear or doors. I would expect gear retraction to start before that height. Could we imagine an air/ground logic fault inhibiting gear retraction and allowing TCMA, which triggered (for whatever reason!) causing dual thrust loss? I would expect this to be in the realms of a combination of failures shown to be extremely impossible, but\x85 2 users liked this post. |
| Xeptu
2025-06-13T13:18:00 permalink Post: 11900511 |
Out of interest about when did the RAT include a hydraulic pump, not that it would be sufficient to retract the gear anyway. |
| dragon6172
2025-06-13T15:16:00 permalink Post: 11900622 |
In
this video
of a 787 take-off, first the inner main landing gear bay doors open, and then the bogies tilt downwards. In the first video of the crash, the bogies appear to be tilted downwards but said doors remain closed?
The video of the crash shows the gear tilted down, which should mean gear up was selected, however something kept the sequence from continuing (loss of hydraulic pressure for example). Discussed here 6 users liked this post. |
| boaclhryul
2025-06-13T17:07:00 permalink Post: 11900700 |
The accident aircraft was a -8 and does not have that feature. Main gear bogies tilt nose down, then gear doors open, then retraction ... The video of the crash shows the
gear tilted down
, which
should mean gear up was selected
, however
something kept the sequence from continuing
(loss of hydraulic pressure for example).
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| appruser
2025-06-13T19:02:00 permalink Post: 11900816 |
Although the gear bogie isn\x92t in the initial post-liftoff position, if you can see the retraction mechanism operating in a 787 It first tilts the bogie forward. I\x92d therefore consider that a \x93gear up\x94 switch was activated but the action failed \x97most likely due to hydraulic pressure loss. In the second video (left-side view), I could interpret that gear retraction begins around 24 s and then halts before 27 s, exactly when the aircraft stops climbing.
Just my two cents, from the perspective of an aircraft engineer with a background primarily in Airbus. |
| tuiallstar
2025-06-13T19:10:00 permalink Post: 11900822 |
The gear is required to be retracted within 12 seconds even on one engine. The fact that it wasn't means it was either not selected or there wasn't engine driven hydraulic pressure to do it.
Out of interest about when did the RAT include a hydraulic pump, not that it would be sufficient to retract the gear anyway. 1 user liked this post. |
| flapassym
2025-06-13T20:04:00 permalink Post: 11900854 |
Question is why both engines lost power . Foreign object ingestion , contaminated fuel or both cutoff levels operated ? We do not know .
Any autothrust discussion is misleading since every pilot in that situation will firewall the levers whatever thrust reduction was selected for TO . the same is true for the RAT discussion- if enough hydraulic pressure was generated or not . The plane pitched up last second so there obviously was control until the end . Of course , without energy pulling alone will not bring you anywhere . Why did both engines fail the same second as they would be cut off ??? Actually not true. Remember the 737 with iced up itt probes that hit the Washington bridge? a simple \x93yugga\x94 on the power levers would have prevented disaster. probably irrelevant to this topic however |
| mechpowi
2025-06-13T22:50:00 permalink Post: 11900977 |
I've been closely examining a video frame captured very early in the footage depicting the aircraft's final moments. In this particular frame, I believe the
left main landing gear (MLG) door is clearly visible in the open position
, while the
right MLG door appears closed
. Additionally, both
main gear bogies are noticeably tilted forward
\x97 a configuration that typically occurs at the initiation of the gear retraction sequence.
This combination strongly suggests that a gear retraction was commanded , but the sequence was interrupted and never completed . What\x92s particularly striking is the asymmetry \x97 the left door open, the right door closed \x97 which should not occur during normal operations and points toward a possible hydraulic failure scenario during retraction. As many will know, on the Boeing 787-8, each main gear door is hydraulically actuated and powered by its respective side\x92s hydraulic system \x97 the left gear door by the left hydraulic system , and the right by the right . This leads me to propose the following hypothesis:
Further supporting this theory are:
In the meantime, my thoughts are very much with all those affected by this heartbreaking event. ( NOTE: Unfortunately this is my first post here. I wanted to upload the frame for all to see but the forum is restricting me from doing this until I reach 8 posts. I can't link to it via a URL either. I studied a frame from the very start of the video, just as the full aircraft enters view and expanded it by 400% allowing me to see the position of the MLG doors). 2 users liked this post. |
| TURIN
2025-06-13T23:16:00 permalink Post: 11900989 |
I have no knowledge about 787, but every landing gear system I\x92ve worked with did not sequence Left and Right MLG to retract and extend with each other. In fact it is typical for left and right side to move at slightly different speed due to different friction etc. Retraction assymmetry is probably not a clue to this mystery.
The 787 landing gear is operated by the centre hydraulic system's two electric pumps. I have no idea why they have posted such nonsense. 1 user liked this post. |