Posts about: "RAT (Deployment)" [Posts: 396 Pages: 20]

Originally Posted by DaveReidUK

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?

Originally Posted by JPI33600

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?

Originally Posted by Squawk7700

Perhaps?

• Takeoff proceeded normally, TOGA used.
  
• Autothrottle entered HOLD mode at 80 knots .
  
• VNAV or FLCH was NOT engaged after liftoff.
  
• Pilot assumed A/T was managing thrust, but it wasn\x92t.
  
• Pilot focused on pitch/flying manually.
  
• Thrust stayed fixed or decayed (if levers were moved).
  
• Speed decayed, aircraft climbed too steeply, energy bled off.
  
• Pilot assumed engine failure due to poor climb response.
  

Boeing SOPs typically include a callout at 400 ft like:

"LNAV" - "VNAV" or "FLCH SPD"

To ensure:

• Proper navigation mode is active
  
• Autothrottle resumes thrust management
  
• Aircraft transitions smoothly into the climb phase
  

Originally Posted by TURIN

But would any of that trigger the RAT and/or cause the emergency lights to come on? (I know, there is only anecdotal evidence from the sole survivor of this).

Originally Posted by Squawk7700

Perhaps?

• Takeoff proceeded normally, TOGA used.
  
• Autothrottle entered HOLD mode at 80 knots .
  
• VNAV or FLCH was NOT engaged after liftoff.
  
• Pilot assumed A/T was managing thrust, but it wasn\x92t.
  
• Pilot focused on pitch/flying manually.
  
• Thrust stayed fixed or decayed (if levers were moved).
  
• Speed decayed, aircraft climbed too steeply, energy bled off.
  
• Pilot assumed engine failure due to poor climb response.
  

Boeing SOPs typically include a callout at 400 ft like:

"LNAV" - "VNAV" or "FLCH SPD"

To ensure:

• Proper navigation mode is active
  
• Autothrottle resumes thrust management
  
• Aircraft transitions smoothly into the climb phase
  

Originally Posted by Icarus2001

Should we talk about the RAT being an electrical generator? No? Okay then, carry on.

Originally Posted by Aerospace101

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.

Originally Posted by Magplug

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

Originally Posted by Magplug

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.

Originally Posted by Magplug

I'm still going with
a) Incorrect derate + low Vspeeds or
b) Low altitude capture

Originally Posted by Irishshamrock

If power was lost at the moment gear was selected \x91up\x92 it would have started the process only for it to stop, hence why the forward tilt was present - perhaps

Originally Posted by brokenenglish

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.

Originally Posted by Sailvi767

I agree with what you posted however the solution is so simple that I can’t believe a professional flight crew would not handle it without much of a blip. Push the trust levers forward.

Originally Posted by brokenenglish

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.

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 EDLB

@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.

Originally Posted by 777ret

The simplest answer: Lo Lvl Alt Cap; Thrust to Idle; Startle Factor; Inappropriate Memory Items : ( RAT deployed; insufficient time for Eng relight.

Originally Posted by Aerospace101

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.

Originally Posted by Pinkman

Presumably the RAT was deployed (with an "humungous" bang) when the residual pressure in the "C" hydraulic system decayed to zero: there was initially enough to tilt the trucks but thats it.