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Aerospace101
June 17, 2025, 09:28:00 GMT permalink Post: 11904137 |
Are you saying that the RAT cannot power retraction of the gear, neither via its own hydraulic pump nor via its generator providing power to the centre system pumps?
Or could it be that it's capable of delivering enough power (via either route) to move the tilt actuator but not a humungous retraction jack? The RAT provides electrical power only to critical flight instrumentation (mostly Captains), navigation and communication. The same critical equipment that the Battery will provide. If all electrics was lost, the main Battery would provides standby power until RAT is fully deployed. The RAT electrical power would not be able to power C hydraulic electric pumps. |
JPI33600
June 17, 2025, 10:01:00 GMT permalink Post: 11904160 |
Not an avionics specialist, but electronics / software engineer here, with extensive experience in hardware fault tracking, protocol monitoring and software debugging in embedded systems : mods, feel free to delete this post if I am completely out of track (and thank you for the huge amount of work you've done trying to keep this discussion clean).
After I have read the whole thread, I think most of the community agrees about a lack of engine thrust being the cause of the crash. Searching in that direction, I'm trying to "think out of the box", discarding the usual suspects (birds ingestion, TCMA, human mistake...), and to find a plausible single point of failure among the various subsystems involved. I was thinking of reversing the causality of the event, i.e. exploring a case where the engines would have behaved unexpectedly because of a major electrical failure, instead of the already explored case where both powerplants went AWOL first. Therefore, I have a couple questions for tdracer / fdr / other informed contributors (BTW, fantastic contribution guys, please keep the good info coming): 1. From the scarce info available, is it reasonable to conclude that the engines were totally shut down? Could they have just been set to idle or reduced thrust instead? 2. In the second case, if (and that's a big IF) a major electrical failure happened first (which could have triggered RAT deployment), and considering this plane is a FBW aircraft, could there exist a case where the FADECs would command idle thrust -- or significant thrust reduction -- because they receive invalid input data from the throttle controls? Kind of a garbage in-garbage out case? The associated scenario would be: major electrical fault (with subsequent RAT deployment) -> major protocol disturbance on ARINC/AFDX buses -> FADECs detect invalid data from the controls -> FADECS enter some kinf of safe mode and command reduced or idle thrust. Does it make sense or is it pure fantasy? |
EDML
June 17, 2025, 10:13:00 GMT permalink Post: 11904168 |
Not an avionics specialist, but electronics / software engineer here, with extensive experience in hardware fault tracking, protocol monitoring and software debugging in embedded systems : mods, feel free to delete this post if I am completely out of track (and thank you for the huge amount of work you've done trying to keep this discussion clean).
After I have read the whole thread, I think most of the community agrees about a lack of engine thrust being the cause of the crash. Searching in that direction, I'm trying to "think out of the box", discarding the usual suspects (birds ingestion, TCMA, human mistake...), and to find a plausible single point of failure among the various subsystems involved. I was thinking of reversing the causality of the event, i.e. exploring a case where the engines would have behaved unexpectedly because of a major electrical failure, instead of the already explored case where both powerplants went AWOL first. Therefore, I have a couple questions for tdracer / fdr / other informed contributors (BTW, fantastic contribution guys, please keep the good info coming): 1. From the scarce info available, is it reasonable to conclude that the engines were totally shut down? Could they have just been set to idle or reduced thrust instead? 2. In the second case, if (and that's a big IF) a major electrical failure happened first (which could have triggered RAT deployment), and considering this plane is a FBW aircraft, could there exist a case where the FADECs would command idle thrust -- or significant thrust reduction -- because they receive invalid input data from the throttle controls? Kind of a garbage in-garbage out case? The associated scenario would be: major electrical fault (with subsequent RAT deployment) -> major protocol disturbance on ARINC/AFDX buses -> FADECs detect invalid data from the controls -> FADECS enter some kinf of safe mode and command reduced or idle thrust. Does it make sense or is it pure fantasy? |
TURIN
June 17, 2025, 11:12:00 GMT permalink Post: 11904212 |
Perhaps?
"LNAV" - "VNAV" or "FLCH SPD" To ensure:
|
Squawk7700
June 17, 2025, 12:33:00 GMT permalink Post: 11904262 |
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McDoo
June 17, 2025, 12:50:00 GMT permalink Post: 11904275 |
What if?
Perhaps?
"LNAV" - "VNAV" or "FLCH SPD" To ensure:
altitude was set on the FGP? Suppose they had left it at zero prior to final departure briefing? Not 787 rated but is it possible that they selected FLCH after take off and the aircraft targeted the zero altitude selection? Doesn\x92t explain the RAT deployment but I have a feeling there maybe more than one hole in this Swiss cheese\x85 |
Aerospace101
June 17, 2025, 13:06:00 GMT permalink Post: 11904288 |
The RAT provides hydraulic power only to the flight control portion of the C hydraulics. Wing and tail flight controls only. Non return valves prevent power to other C hydraulic powered systems like the gear.
The RAT provides electrical power only to critical flight instrumentation (mostly Captains), navigation and communication. The same critical equipment that the Battery will provide. If all electrics was lost, the main Battery would provides standby power until RAT is fully deployed. The RAT electrical power would not be able to power C hydraulic electric pumps. |
mechpowi
June 17, 2025, 15:25:00 GMT permalink Post: 11904394 |
RAT powered systems
There’s been some debate over what electrical and hydraulic systems are powered. According to one unauthorized and Not For Flight -labeled FCOM copy that seems quite authentic:
“In-Air Rat Only Operation” mode (Standby Power) – If loss of all electrical power to captain’s and first officer’s flight instruments occurs in flight, the RAT energizes the captain’s flight instruments and other essential equipment for flight controls, navigation, and communication. The main battery provides standby power until RAT deployment. Significant loads energized by this mode include:
captain’s inboard DU • captain’s outboard DU • lower DU • autoflight system • MCP • autopilot • captain’s / first officer’s ACP • captain’s / first officer’s flight interphone • VHF L • TCP L • DSP L • MFK L • CCD L • IRU L, R • AHRU L, R • INR L, R • ISFD • FMC • PFC • CCR L • center pitot heat • engine/APU fire detection • miscellaneous lightin Note: Autothrottle, flaps, slats, stabilizer, thrust reversers, auto speedbrakes, air conditioning / pressurization, Head-Up displays, HF radios, SATCOM systems, external lighting, WIPS, and window heat are inoperative on standby power. “In-Air Battery Only” mode (Standby Power) – This mode energizes the same equipment as the “In-Air RAT Operation Only” mode with the exception of center pitot heat. Last edited by Senior Pilot; 17th June 2025 at 21:44 . Reason: Remove false information |
rkenyon
June 17, 2025, 17:19:00 GMT permalink Post: 11904487 |
B787 Skipper.... No longer able to sit on my hands!
The joker that published one or other of the fictional accident reports before the dead are even identified needs stringing up by the thumbs.... Well done mods. OK, some of these theories, just bearing in mind the the flight recorder (there is only one FDR + CVR combined) was in the intact section of the undamaged tail and has been with the authorities for almost five days...... - All you guys who are rushing down the TCMA rabbit hole: If it was established that a software error drove both engines to idle without warning, after rotate.... Don't you think the worldwide fleet of B787s would have been grounded by now? Such a glaring failure would be absolutely inescapable on the FDR. Whatever was wrong with this aircraft was present at rotate, unbeknown to the crew. The fact that no ADs or notices to operators have been issued usually means that the cause is known and the aircraft was serviceable. The statement from a prominent Indian Captain about the skill and tenacity of the crew, right up to the last minute is absolutely laudable. However, the cynic in me says that the way is being paved for some bad news and by that I mean news that will do Air India reputational damage. Expect more management of expectation in the coming days. I'm still going with a) Incorrect derate + low Vspeeds or b) Low altitude capture
Speaking as a B787 Captain..... There is so much rubbish and stupid suggestion being written here.
- 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. |
Aerospace101
June 17, 2025, 17:44:00 GMT permalink Post: 11904511 |
I appreciate some don\x92t want to speculate on the RAT deployment or APU auto start until further evidence, but the gear truck tilt is a massive clue to a non-normal hydraulic issue, most likely caused by electrical power problems since C hydraulics is only electric pump powered. |
Aerospace101
June 17, 2025, 19:01:00 GMT permalink Post: 11904572 |
1. The hydraulic failure happened exactly when the truck had tilted forward but the split-second before the gear doors could open. That exact timing seems too coincidental. 2. The crew selected Gear Up. We have no proof of this. I speculate the crew never got as far as "Positive Rate...Gear Up" because they were already engrossed in flying the aircraft and processing their thrust problem. If an electrical problem had developed (as evidenced by the RAT deployment) the flight instrumentation would have been flickering and a flurry of silent master caution alerts would be very distracting. I suggest it's more likely that the truck remained in a forward tilt from the takeoff run because the hydraulic failure happened prior to rotation, therefore keeping it in this unusual position. This answer does not rely on the gear lever position either. It also insinuates that their hydraulic problems occurred probably between V1 and VR. See my earlier post . |
KSINGH
June 17, 2025, 22:42:00 GMT permalink Post: 11904730 |
Most? The Airbus I'm familiar with is 100' AGL or 5s after liftoff and I think this is common to all Airbus FBW. The B787 & B777 appear to be 200' AGL but I'm taking this from online FCOM extracts. The
B737
does appear to be 400'. Company limitations may be higher.
As mentioned elsewhere both EK and Air NZ have had messy low level mis-set altitude capture incidents with the B777, but in isolation, obviously, this wouldn't cause RAT extension. About airport cameras. Someone pointed out on the other thread that airports have more coverage than they would necessarily advertise. Presumably available to investigators but not to the public or press. yeah the low MCP alt setting/alt capture doesn\x92t make a whole lot of sense- the plane didn\x92t pitch forward it just failed to climb/lost lift that\x92s not conducive with what happened nor does it explain why the gear is still down (although seemingly selected up given the boogie tilt) or the RAT deployed (if it really was) |
Chiefttp
June 18, 2025, 00:09:00 GMT 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. |
FullWings
June 18, 2025, 08:46:00 GMT permalink Post: 11905031 |
Most? The Airbus I'm familiar with is 100' AGL or 5s after liftoff and I think this is common to all Airbus FBW. The B787 & B777 appear to be 200' AGL but I'm taking this from online FCOM extracts. The
B737
does appear to be 400'. Company limitations may be higher.
As mentioned elsewhere both EK and Air NZ have had messy low level mis-set altitude capture incidents with the B777, but in isolation, obviously, this wouldn't cause RAT extension. About airport cameras. Someone pointed out on the other thread that airports have more coverage than they would necessarily advertise. Presumably available to investigators but not to the public or press. The ideas of mis-set MCP, AT modes, etc. were worth exploring but by this point, like the gear/flap/performance ones, there is enough convincing evidence now that a) the takeoff was normal until it suddenly wasn\x92t and b) none of the above would cause RAT deployment and a glide into the ground. |
Bap7788
June 18, 2025, 11:50:00 GMT permalink Post: 11905173 |
Hi all,
Disclaimer: I read this thread from hour 1, still scratching my head regarding perf though. I know sound analysis points to higher odds being a dual engine failure with RAT deployed, however I still have some questions if anyone is available to enlighten. So, my questions is related to T/O performance. Is it possible on the 787 to calculate perf in the OPT for F15/20 T/O, and to enter F5 T/O speed on the FMC ? By that I mean do normal procedure, but at the point where you are suppose to enter flaps, CG speed ect…. You, out of habit (if F5 is indeed a habit on the 787) enter F5, but F15/20 speeds ? Or would there be a warning that you have manually inputed speeds that are not correct for the selected flaps and conditions inputed in the FMC ? Thanks for the help ! |
mechpowi
June 18, 2025, 12:13:00 GMT permalink Post: 11905186 |
Hi all,
Disclaimer: I read this thread from hour 1, still scratching my head regarding perf though. I know sound analysis points to higher odds being a dual engine failure with RAT deployed, however I still have some questions if anyone is available to enlighten. So, my questions is related to T/O performance. Is it possible on the 787 to calculate perf in the OPT for F15/20 T/O, and to enter F5 T/O speed on the FMC ? By that I mean do normal procedure, but at the point where you are suppose to enter flaps, CG speed ect\x85. You, out of habit (if F5 is indeed a habit on the 787) enter F5, but F15/20 speeds ? Or would there be a warning that you have manually inputed speeds that are not correct for the selected flaps and conditions inputed in the FMC ? Thanks for the help ! |
777ret
June 18, 2025, 22:38:00 GMT 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. |
nachtmusak
June 19, 2025, 01:00:00 GMT permalink Post: 11905642 |
My understanding of altitude capture is that the autopilot will automatically adjust both thrust and pitch to intercept the requested altitude. However to my eyes there is very little pitch adjustment in the CCTV video of the plane taken from behind, until the very end of the video when it pitches up somewhat (obscured by buildings, more visible in the smartphone video). Please correct me if I'm wrong but I'd have thought that if the autopilot was trying to capture a very low altitude it would start pitching down (quite noticeably!) to do so, not remain at what looks like 10+ degrees nose-up. I honestly struggle to reconcile what I'm looking at in the video with an attempt to level off at 0ft, 200ft, or any of the other mentioned low-level altitudes. Also maybe I'm missing something 787-specific but generally doesn't the autopilot have to be activated for the aircraft to automatically attempt to capture the pre-selected altitude? That was the case in this incident involving a Dash 8 and a target altitude of 0 feet that I am reading about ( https://www.gov.uk/aaib-reports/aaib...-dash-8-g-ecoe ). I'd have thought the PF would still be hand-flying the departure at the point that things went wrong, considering that the gear hadn't even been retracted yet... |
Pinkman
June 19, 2025, 07:55:00 GMT permalink Post: 11905808 |
I too watched his explanation with interest. However I believe he is not considering the possibility of C hydraulics failure prior to wheels lift-off, because I speculated this is the more likely reason the gear trucks remained in a forward tilt position,
see my earlier post here
. I believe the crew never got as far as calling for the Gear Up... many possible reasons for this, flickering instrument screens during the electrical switchover to battery power, flurry of EICAS messages. For any of those things happening around time of rotation, I would be advocating delaying gear up decision until safely climbing away above AA and as a crew you have chance to discuss safest course of action. Not putting the gear up shouldn't kill you.
Point is the gear truck tilt is a clue of a C hydraulics failure, but we cant determine if hydraulics failed prior to wheels off runway or prior to gear doors opening in retraction sequence. |
Aerospace101
June 19, 2025, 08:27:00 GMT permalink Post: 11905828 |
Last edited by Saab Dastard; 19th June 2025 at 10:58 . Reason: Reference to deleted post removed |
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