Posts by user "mechpowi" [Posts: 18 Total up-votes: 32 Pages: 1]

Originally Posted by gdandridge

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:

1. Shortly after rotation, with a positive rate of climb established, the flight crew commands gear up .
   
2. The gear retraction sequence initiates ; the main gear bogies tilt forward , consistent with the start of retraction.
   
3. The right engine fails first , resulting in a loss of right hydraulic system pressure . Consequently, the right MLG door does not open .
   
4. The left MLG door, still powered by the left hydraulic system, opens .
   
5. Moments later, the left engine also fails , leading to loss of the left hydraulic system . With the door now open but no remaining hydraulic pressure, the left main gear remains extended and the door remains open .
   
6. The ram air turbine (RAT) deploys , consistent with total engine and electrical power loss.
   
7. With the loss of thrust from both engines , the aircraft loses lift and enters an unrecoverable descent, tragically ending in impact.
   

This sequence would explain the partially completed gear retraction and the asymmetric gear door position observed in the video evidence. It\x92s worth noting that the timing of the hydraulic losses would have to be very close together \x97 potentially within seconds \x97 which aligns with a dual engine failure shortly after take-off . In such a scenario, asymmetric thrust would be minimal or non-existent , making the aircraft\x92s attitude appear otherwise stable in its descent.

Further supporting this theory are:

• Eyewitness reports of a loud bang , possibly indicating an engine failure.
  
• A mayday call reportedly made by the crew.
  
• The audible presence of the RAT in the video, suggesting a complete loss of engine-driven electrical and hydraulic systems.
  
• The noticeable absence of typical engine noise , supporting the hypothesis of dual engine failure.
  

This scenario would offer a tragically plausible explanation for the aircraft\x92s behavior and the observed configuration in its final moments. Of course, the official investigation will provide the definitive answers , and we must await their findings.

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).

Originally Posted by SteinarN

I would say an average passenger has problems differentiating between thrust and G.
Even after engines lost all power G could still vary quite a bit as the pilots tried to crash with as little energy as possible. Any passenger could feel this varying G as varying thrust instead.

Originally Posted by Sisiphos

Hmm. Not sure where the idea comes from the gear was partially retracted... I can't see any signs for it on the video, nor can I see a RAT. and just to say "some event" must have happened is not very helpful, is it? Of course "something" has happened, but the question remains what.

Would it not make more sense to assume there is no RAT if no RAT is visible?

Could it be that we as pilots are in general biased to find a technical reason, although we all know the vast majority of accidents are down to human error?

Originally Posted by Kraftstoffvondesibel

It was hard to let it go, so I spent a bit more time with the audio, using filtering and matching to see if I could be even more sure.

It's a pity uploading audio to this site isn't as easy as uploading photos, but I can say it took very little filtering and matching to make the Air India audio become nearly indistinguishable from audio taken of B787 with known RAT extended during landing.

I can't see it in the photos either, but in these circumstances the audio is a lot more trustworthy, and from my audio point of view RAT deployment is 100% confirmed.

In the off chance that the audio I borrowed from a confirmed RAT event was somehow faked, I plotted the technical data I could find of the B787 RAT (4000rpm, 2 blades) combined with a height estimate and asked the O3 model with deep research to estimate doppler shift and speed.
The result matches the above documented 270-200Hz (in one of the harmonics) Doppler shift observed in 1.7 seconds.

Originally Posted by uncle_maxwell

Woulda shoulda coulda and might not have changed this particular outcome, but is there a case in taking off with APU ON? It would give some level of redundancy for electrics and hydraulics and perhaps avoid the added shock and workload of losing thrust, electrics and hydraulics pretty much simultaneously in a rare scenario like this one. During Hudson river accident, APU ON was the first thing Sully did (apart from saying \x91my aircraft\x92) but he had more altitude and speed and electrics and the gear up. I know there are other considerations for using or not using APU depending on flight phase, but if it is safe and within design parameters, perhaps SOPs should give pilots discretion on whether or not they use the APU for critical flight phases? Just a thought.

Originally Posted by Captain Fishy

What if the PF called stop just before V1 and closed the thrust levers but either changed his mind or was overridden by the other pilot, who rapidly pushed the thrust levers back up. Could this trigger a TCMA intervention and subsequent dual engine shutdown as it was still on the runway at this point? Hopefully not.

Originally Posted by Wannabe Flyer

a slight more precise translation as a native speaker. \x93After take off it felt as if we were still in one place & not moving. Then the sound of the engines racing (common Indian term for revving of engines on bikes & cars with the clutch depressed) & then green & white lights came on in the cabin as we hit something.\x94 In my opinion the race sound he talking about sounds like engine surges if compared to race.

Originally Posted by fgrieu

Based on the video taken from the left of the flight path, can we determine at what point of the runway rotation occurred? Is there positive confirmation that the takeoff roll started at the beginning of the runway ? Are the two indicative of trouble before rotation, as the Times states ?

Source: https://www.thetimes.com/world/asia/...rash-vhqw6b7v3 (paywalled)

Originally Posted by JG1

Could it be possible that in the software the 'position-eng-fuel-switch-left' =ON and the 'position-eng-fuel-switch-right=ON' can both changed to OFF by a electric/software issue? So without movement of the actual physical switches the system senses a shutdown command?

Originally Posted by fgrieu

Based on the video taken from the left of the flight path, can we determine at what point of the runway rotation occurred? Is there positive confirmation that the takeoff roll started at the beginning of the runway ? Are the two indicative of trouble before rotation, as the Times states ?

Source: https://www.thetimes.com/world/asia/...rash-vhqw6b7v3 (paywalled)

Originally Posted by TURIN

I'm pretty sure the software is written independently. Same as Airbus, you don't want the same software error on duplicate critical systems.

Originally Posted by bbofh

If a gear retraction remains in "tilt", then what does that interregnum status say in response to various systems' interrogations of the WoW sensors? Is it stuck in the Netherworld of betwixt and between ?
Perhaps the safer solution should be an additional circuitry micro-switch feed of all three "up and locked"? (that agrees with the gear-handle).
Also waiting to hear what the 787-8 RADALT status is? Was it ever 5G emanations-proofed?
Is there any software provision for the TCMA to know for sure that the gear is neither up nor down? I would doubt it. Does that uncertainty affect the thrust-lever's positional input?

Originally Posted by Bap7788

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 !

Originally Posted by syseng68k

Lead Balloon:



\x93The "requirement" for TCMA was "specified" by the FAA. Manufacturers seeking certification of aeronautical products subject to the requirements then had no choice but to design and instal systems that met the FAA's certification requirements\x94.

I think that has already been established upthread.


\x93I'm pretty sure it's clear what "sources", other than TCMA systems if any, have "authority to issue an engine shutdown command", though it does depend on what you mean by "engine shutdown".\x94

I don\x92t think that is clear at all. The shutdown hypothesis, if true, both engines, makes it likely that they were commanded to do so. While the discussion has centered around the TCMA subsystem, if other subsystems have the ability to do that, they need to be defined and looked at as well.

Originally Posted by syseng68k

mechpowl:
Thanks for that. That begs the question, if there is overspead protection already, perhaps multiple channels and sensors, why is TCMA needed at all ?. Blanket overspeed protection already covers the underlying requirement, ie: prevention of overspeed, all cases. Seems to be adding complexity for no reason.

Originally Posted by Shep69

Hmmmmm\x85.then I wonder how the auto throttles will behave if a low stop height if the MCP is mis set \x97 potentially below 400\x92 AGL. Will they stay in hold, will they go to SPD, or will they engage in THR REF.

I never tried this in the sim on the 777 so I\x92m not sure. I was grateful that the 777 would change to SPD mode on initial altitude capture (as opposed to the -400 VMo here we go). It\x92s been a few years in any case though.