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dragon6172
2025-06-17T01:30:00 permalink Post: 11903903 |
I previously speculated the forward truck tilt was proof the gear had been selected UP and the retraction sequence was interrupted.
I\x92m not so sure now and believe there is a different conclusion from this non-normal gear position. In normal retraction sequence the gear doors open almost instantaneously after the forward truck tilt. It does seem coincidental the tilt was completed while no indication of the doors opening is visible on the rooftop video, which would suggest hydraulic failure at that exact moment; this precise timing of interruption in the retraction sequence feels unlikely. So is there a more likely answer for the forward truck tilt that does not involve movement of the gear lever? I suspect it\x92s more likely that C hydraulics lost power prior to rotation, as a consequence the truck could not tilt rearward during rotation as it normally should. Therefore it\x92s probable it always stayed in a neutral or forward tilt position from the take off run until we see it in the rooftop video. If the gear was behaving normally, and the crew had omitted to retract, it should be hanging rearwards. Watch any 787-8 takeoff video and you can see at rotation all 4 main wheels stay on the runway as the aircraft rotates. Just after wheels up they tilt rearwards. It\x92s a very subtle position change. If the gear was always in a neutral or forward truck tilt position then this undermines the theory that retraction sequence was interrupted. It insinuates the C hydraulic and electrical failure happened prior to main wheels lift off. For this reason I believe we cannot assume that gear UP was selected nor that retraction was interrupted. I\x92m seeing lots of social media posts which suggest the forward tilt means gear was in retraction and I don\x92t believe it was now. I think the truck tilt position is key to understanding the timeline of system failures and whether the automatic RAT deployment was triggered by power failures or engine(s) failure. The question remains, did loss of center hydraulics happen before or after loss of thrust? In a normal retraction, the main gear doors begin to open before the truck tilt is complete (roughly when the gear trucks are "level", seen around 8-10 second marks of this video ). The nose gear doors open at the same time the main gear tilt starts (seen in Jetstar video linked below). It's too blurry in the video/stills of the accident aircraft to definitively say the nose doors are not open, but I'd say no. And it's pretty much a certainty that the main gear doors are not open. And finally I think it is also pretty clear that the main gear trucks are tilted down to the retract position. I have no confirmation of this, but I read (or heard someone say in a video) that the truck tilt actuator was a "single acting" actuator, meaning hydraulic pressure held it in the toe up position and it was spring loaded to the retract position. Which means if hydraulic pressure was lost due to loss of power to the electric driven center hydraulic system, then the main gear trucks would tilt forward on their own without moving the gear handle. The Jetstar burst tire video somewhat backs this up, in that the blown tire caused a leak to the center hydraulic system and an alternate extension was required (thus the reason the main doors are down during the landing). No hydraulic pressure means the main gear trucks remained pointing nose down during the landing. Video here Last edited by dragon6172; 18th Jun 2025 at 03:01 . Reason: Edit video links 3 users liked this post. |
bbofh
2025-06-17T03:27:00 permalink Post: 11903939 |
WHEN something catastrophic happens, like dual engine failure, that then creates a query about any "duality" between two standalone systems that really should have nothing whatsoever in common... except the PF.
Nothing in common? Is that really the case for the 787-8 in the Air India 787 crash? Look at these three TCMA-related links in the order presented and note the proforma prescriptive caveats in the first two: https://downloads.regulations.gov/FA...tachment_1.pdf https://downloads.regulations.gov/FA...tachment_1.pdf https://patents.google.com/patent/US6704630B2/en TCMA is designed to detect and accommodate single failures within the EEC/FADEC, preventing a failure from jeopardizing the safe operation of the aircraft. Implementation: It involves implementing specific software changes within the engine's control system (EEC). Regulation: After some incidents, the design change was mandated by regulators, with a deadline for production aircraft by December 31, 2018, and a retrofit plan for existing aircraft. Boeing 787 Application: The TCMA feature is specifically relevant to the 787-8 equipped with GEnx-1B engines, but it may also be applicable to other 787 variants using the same engine type. The first two links are respectively the request for and FAA affirmation/approval for a GENx-1b software system called TCMA (Thrust Control Malfunction Accommodation). TCMA is the system that precludes High Uncommanded Thrust (HUT) after touchdown by fuel-chopping the engines. It is designed to avoid runway departures. One input is power-lever position. It's then fair to say that (additionally) Air/Ground sensing is quintessentially vital (as to when the system is "armed" and can do this fuel-chop). The third link is the complex description (with diagrams) of the patent application's design functionality of TCMA. FROM THE 3rd link above: "​​​​​​The method of the present invention compares the engine's actual power level with a threshold contour defined by the TCMA software package. When the TCMA software package determines that a thrust control malfunction has occurred, based on the engine's power level exceeding the threshold contour, the engine is shut down by the TCMA circuit." It is also notable that it says within the 3rd link that "Typically the aircraft is allowed to operate for a limited period of time with just a single operative processing subsystem." That Air India 787 was not long out of maintenance. We are then motivated to ask "what dictates the Air/Ground sensing". Is it just a Weight-on-Wheels microswitch or a RADAlt? (or both? or triplicated micro-switches?). We may then ask: "Did Air India implement the post-5G changes to their RADAlts that concentrated on maintaining their auto-land capability (in the face of 5G interference with RADAlts?) I seem to recall that the FAA's dictums on this pointed out that it was an individual nation's responsibility to both control their 5G frequency spectrums and implement changes to Radar altimeters that would work interference-free in critical phases of flight. What has the Indian regulator done in this regard as the responsible entity? The whole shemozzle, starting with the US Federal Communications Commission (FCC) spectrum allocations, was an ongoing fight between the telecom giants and their getting their new mobile tech to market. So where are we going with this line of causal reasoning? The only commonality/duality between left and right engines is the software driving the TCMA as monitored by the TCMA software incorporated in each engine's EEC. Most pundits have identified the gear-tilt as evidence that only the centre electrically-driven pump can do the gear-tilt if the engines' other two hyd systems are suddenly both in QUIT mode (which accords also with the instant RAT deployment and loud noise heard by the sole survivor) - and an ensuing transition from climb-out to a deadly sinking and commensurate attitude change for speed maint. My unavoidable conclusion is that the selection of gear UP and the breaking of the gear downlocks (and WOW sensing and energization of the RADALTs) called upon the TCMA to fuel-chop the engines (via the TCMA functionality in each engine's EEC). We could start by looking at the No Break Power Transfer (NBPT) tech used in modern airliners. This has led to Gen Control Panel meltdowns in 777's due to GEN contact meltdown. I know of one instance when a 773 was reduced to a RAT only landing enroute and another where a disastrous MEC fire occurred after start on pushback at LHR. A description of the systems glitch often experienced is at the following link. It's quite apparently a "gear-up" hiccup with potential damning consequences for smooth TCMA operation. As to be seen in the quality videos, a fuel-chop provides no real clue (such as engine failure/smoke/fire classically does). An uncommanded "reset" of the two engine's TCMA's upon gear retraction (link below) is trackable to be the sought after "duality" leading to a "both simultaneously quit" engine failure. These momentary electrical glitches and instant "resets" are described in the two links below. Food for reasoned thought? https://tinyurl.com/yn5ce4tz https://tinyurl.com/3kkh6n3d 3 users liked this post. |
dragon6172
2025-06-17T03:57:00 permalink Post: 11903950 |
Most pundits have identified the gear-tilt as evidence that only the centre electrically-driven pump can do the gear-tilt if the engines' other two hyd systems are suddenly both in QUIT mode (which accords also with the instant RAT deployment and loud noise heard by the sole survivor) - and an ensuing transition from climb-out to a deadly sinking and commensurate attitude change for speed maint.
No idea. I only got that info from the Master MEL on the FAA website. According to the MMEL the aircraft can be dispatched as long as there is one of each type sensor working on each main gear. (AIs MEL could be more restrictive) |
Aerospace101
2025-06-17T09:28:00 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. 8 users liked this post. |
JPI33600
2025-06-17T10:01:00 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? 3 users liked this post. |
EDML
2025-06-17T10:13:00 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? 1 user liked this post. |
TURIN
2025-06-17T11:12:00 permalink Post: 11904212 |
Perhaps?
"LNAV" - "VNAV" or "FLCH SPD" To ensure:
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Squawk7700
2025-06-17T12:33:00 permalink Post: 11904262 |
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McDoo
2025-06-17T12:50:00 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 3 users liked this post. |
Aerospace101
2025-06-17T13:06:00 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. 3 users liked this post. |
mechpowi
2025-06-17T15:25:00 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 Jun 2025 at 21:44 . Reason: Remove false information 6 users liked this post. |
rkenyon
2025-06-17T17:19:00 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. 7 users liked this post. |
Aerospace101
2025-06-17T17:44:00 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. 7 users liked this post. |
Aerospace101
2025-06-17T19:01:00 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 . 3 users liked this post. |
KSINGH
2025-06-17T22:42:00 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
2025-06-18T00:09:00 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. 3 users liked this post. |
FullWings
2025-06-18T08:46:00 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. 3 users liked this post. |
Bap7788
2025-06-18T11:50:00 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
2025-06-18T12:13:00 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
2025-06-18T22:38:00 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. 3 users liked this post. |
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