Posts about: "Hydraulic Failure (All)" [Posts: 103 Pages: 6]

barrymung
2025-06-12T16:17:00
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Post: 11899426
Originally Posted by Kerosine
Given the sound which clearly mimics the RAT, images and collective tech knowledge, what could lead to this symmetric loss of thrust/lift at 200ft?

Fuel supply/quality issues?
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.

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Speedbird744
2025-06-12T16:18:00
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Post: 11899430
Originally Posted by KSINGH
You are saying the RAT is deployed but we can rule out engine failure?

I thought this was meant to the *professional* pilot\x92s forum

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
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Post: 11899534
Originally Posted by AirScotia
What is the precise trigger for the RAT to deploy automatically on the 787? Full failure of both engines?
In flight, the RAT deploys automatically if any of the following occur:
• 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
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Post: 11899550
Originally Posted by barrymung
Ok, so...



But, what do flaps do in the event of a major hydraulic/electrical failure? Is there a default that they revert back to? I was under the impression the RAT can't power the flaps?
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.
nachtmusak
2025-06-12T19:29:00
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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.
FlightDetent
2025-06-12T19:38:00
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Post: 11899657
Originally Posted by nachtmusak
Question: would the ram air turbine (if truly it was deployed) have been capable of providing hydraulic power at their airspeed & altitude?
Possibly yes. The single-aisle, non-ETOPS and 30 yrs older design I am familiar with has a cutoff speed of 140 kts. V2 for 98% real-life scenarios is higher than that. No reason for the 787 to be any less capable.
aeo
2025-06-13T06:43:00
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Post: 11900069
Originally Posted by oceancrosser
And your post squarly falls within the categories you describe in your first paragraph. I have, and still am flying 757/767s, flown probably around 40 examples from early to late production planes AND EVERY SINGLE ONE had a RAT.
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 .
Captain Biggles 101
2025-06-13T08:07:00
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Post: 11900140
There isn't enough clarity on numerous issues, and without answers to the following, zero conclusions can be made as to a possible cause. This is definitely one that could go in numerous directions. Anyone claiming to have the definitive answers must have the FDR data, and I'm assuming that shouldn't take too long to be located and analysed.

1a. Were flaps deployed at start of take off roll?
1b. Were flaps retracted coinciding with climb rate reduction?
2. Did the RAT definitely deploy? The videos are grainy low quality. AI improvement surely isn't reliable.
3. If the RAT deployed, would that indicate complete power loss?
4. Was there any other audio indicating thrust loss or variations during departure?
5. Can we confirm the pilot Mayday indicating thrust loss? If so, that needs investigation as a first priority. The pilot was telling us the cause. Unless we have alternative information he should be believed.
6. Why was the gear not retracted? Distraction, hydraulic failure, flap instead of gear, intentionally, the possibilities are endless.
7. If complete thrust loss occurred, other than a severe fuel issue, what could cause simultaneous flameout? That would be almost unimaginable, yet this is what the pilot allergy said happened. It would have massive ramifications if that gets confirmed.

I don't think the video clips we have are clear enough to say anything at all at this stage. Flaps are hard to see on 787 imo for departure settings. All I can say is it appeared to climb well in the first seconds, then coinciding with the point that gear would usually be retracted, lift appears to very quickly be lost. That indicates sudden speed loss, or lift loss. Speed loss would be thrust, lift loss would be flap retraction if thrust was still available.

The pilot allegedly reported thrust loss, that should be highest on the list of causes imo. In the case of double engine failure without any apparent outside influence visible on videos, that would be quite something for investigators to fathom.

I don't know if anyone has data to show speed trend at the point the aircraft starts to descend, or a better audio for thrust variations at that point. I'm guessing that the update frequency on FR24 would be too slow to show that sudden change at the highest point achieved.

We'll have the answers soon enough, all I can say is there appears to be no clear answers here without the data recorders or clear improved information. Indeed no conclusions whatsoever can be made as to crew actions either.

RIP crew and passengers, condolences to the families.

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nachtmusak
2025-06-13T12:20:00
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Post: 11900441
Originally Posted by X-37
20+ years retired 777 Captain so not at all up to speed..
If you selected gear up but at that moment or just before there was a dual engine failure, would the gear move?
Just curious as to how things work.
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.
aerobat77
2025-06-13T12:44:00
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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
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Post: 11900474
Originally Posted by Hl288
Still no one talking about the landing gear position?
A 787-8 with the landing gear down should have the bogey tilting upwards. Clearly in the video, the bogey is tilting downwards, which would indicate something on the aircraft is not working 100% as it should.
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.​​

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sSquares
2025-06-13T12:48:00
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Post: 11900479
Originally Posted by aerobat77
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 ???
I was thinking the same thing.

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
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Post: 11900487
Originally Posted by aerobat77
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

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Xeptu
2025-06-13T13:18:00
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Post: 11900511
Originally Posted by sSquares
I was thinking the same thing.

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?
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.
dragon6172
2025-06-13T15:16:00
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Post: 11900622
Originally Posted by EDMJ
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?
That is a -9. On -9 and -10s the inboard gear doors open at lift off automatically without gear up being selected. The accident aircraft was a -8 and does not have that feature. Main gear bogies tilt nose down, then gear doors open, then retraction as seen in this video

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
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Post: 11900700
Originally Posted by dragon6172
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).
Was wondering about this since bogie attitude was first mentioned a while back. Perhaps someone familiar with the electrical/hydraulic aspects of main retraction on a -8 could comment on what (or loss of what) would prevent the sequence from continuing.
appruser
2025-06-13T19:02:00
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Post: 11900816
Originally Posted by Raffael with FF
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.​​
Thank you, and to HI288 too! this combined with the FR24 blog post about adsb loss just over the runway threshold, and the latest DGCA ask for Air India 787 maintenance adds more weight to the theory, IMO, that there was a major technical issue in play here.
tuiallstar
2025-06-13T19:10:00
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Post: 11900822
Originally Posted by Xeptu
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.
Gear is actuated from Centre system hydraulics which is pressurised by two AC electric pumps not the engines.

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flapassym
2025-06-13T20:04:00
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Post: 11900854
Originally Posted by aerobat77
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
Magplug
2025-06-13T22:13:00
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Post: 11900963
Speaking as a B787 Captain..... There is so much rubbish and stupid suggestion being written here.

This aircraft was airborne for a grand total of 22 seconds, half of which was climbing to no more than 150' aal.

- No Flaps? Due to the setup of the ECL it is physically impossible to go down the runway without some sort of take-off flap set. The T/o config warning would have been singing it's head off. Despite assertions to the contrary I have seen no video clear enough to detect a lack of flaps.

- RAT out? Almost impossible, I have seen no quality footage that definitively witnesses the RAT being out. Those who think they car hear a RAT type noise might be listening to a motorcycle passing or similar. It takes a triple hydraulic failure or a double engine failure to trigger RAT deploment. They happily went through V1 without a hint of rejected take off so as they rotated the aircraft was serviceable. These are big engines, they take a long time to wind down when you shut them down. I have never tried it however engine failure detection takes 30s or for the aircraft to react and they were not even airborne that long.
- Flaps up instead of gear? The B787 flaps are slow both in and out. Given that the 'Positive rate' call is not made the second the wheels leave the ground, a mis-selection of flaps up would not cause any loss of lift for at least 20 seconds, by which time they had already crashed. I believe the gear remained down not because of mis-selection but because of a major distraction on rotate.

Discounting the impossible, two hypotheses remain:

1. Invalid derate set through incorrect cross-checking. Trundling down the runway takes very little power to reach Vr. It is only when you rotate that you create more drag and discover that you do not have sufficient thrust vs. drag to sustain a climb. Or....
2. Put 200' as the altitude target in the FCU. Immediate ALT capture and all the power comes off. PF is still hand flying trying to increase pitch but is already way behind the aircraft.

It could be after this that Boeing are forced to review the B787 practice of exploring the very edges of the performance envelope.

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