Posts about: "RAT (All)" [Posts: 683 Pages: 35]

Originally Posted by guided

Can we focus on theories explaining the facts? Specifically:

• Aircraft used almost the whole runway (3500m)
• Flaps found on the ground in setting 5
• RAT deployed
• Mayday that they lost power

this rules out flap up instead of gear up , selecting wrong autopilot setting, gear up causing electrical faults (as problems started earlier - using up all runway). Something must have happened on the runway (after v1?) that led to loss of electrics (and dual engine failure, maybe later?)

Originally Posted by amsm01

(Sorry, Airbus here and not familiar with Boeing) Flap 5 to 1 reduction on the Boeing triggers autothrust reduction, is that correct? If so, are there any other conditions that need to be met for this to happen like being in some kind of takeoff mode? Just thinking whether this would have potential otherwise in other regimes to cause issues, discontinued approach perhaps.

Am slightly puzzled as to why if flap reduction triggering climb thrust is part of the standard logic (and presumably clean-up technique) then partial dual thrust loss wouldn’t be immediately recognised as the classic symptom of gear / flap retraction handling error? I presume Boeing pilots / air India are just as aware of this it as everyone else, strikes me as odd that one would immediately go into full dual EF mode. My instinctive reaction without knowing the Boeing would be to firewall both TLs, would this have worked in the early flap retraction logic scenario? Many thanks all

Originally Posted by The Brigadier

I see Times of India is reporting the last call to ATC was "Thrust not achieved\x85 falling\x85 Mayday! Mayday! Mayday!" Ahmedabad Air India crash: Long runway roll hints at thrust failure, black box key to probe; officials reveal final moments in cockpit | Ahmedabad News - Times of India

Given the evidence now in the public domain of RAT auto-deployment and simultaneous roll back, with no bird strikes, the most plausible primary trigger is a simultaneous, fuel-related thrust failure on both GEnx-1B engines. Simultaneous FADEC failure seems less likely, at least without tampering.

Originally Posted by The Brigadier

I see Times of India is reporting the last call to ATC was "Thrust not achieved\x85 falling\x85 Mayday! Mayday! Mayday!" Ahmedabad Air India crash: Long runway roll hints at thrust failure, black box key to probe; officials reveal final moments in cockpit | Ahmedabad News - Times of India

Given the evidence now in the public domain of RAT auto-deployment and simultaneous roll back, with no bird strikes, the most plausible primary trigger is a simultaneous, fuel-related thrust failure on both GEnx-1B engines. Simultaneous FADEC failure seems less likely, at least without tampering.

Originally Posted by old dawg

Retired engineer here. Following my post a while ago on the avionics electrical system I have read all the posts and also noticed mention of the hydraulics system.
Returning to my original source, which is Book 1 Introduction to B787 Avionic/Electrical, I read on p. 96 that the RAT will deploy if any of three condions are met.
Maybe the URL will work this time
https://fliphtml5.com/quwam/qhdw/Boo...ics_Electrical
These conditions for deployment of the RAT specifically are:
Loss of both engines
Loss of power to the instrument buses
Loss of all three hydraulic systems

The latter one may be worth a close look because it would appear that problems took place when the wheels left the runway and I assume there was a change of states in various sensors. I surmise these sensors are different from the engine systems where both commands and power are needed to force a change of state in, say, fuel pumps. Is it the same for thrust control?
It says there are three hydraulic systems but is there a common reservoir? I'm not an expert in that field but google tells me that B787 has a bootstrap reservoir system which I understand to mean that a pressure of 5000 psi is maintained using a piston arrangement.

At this point think timeline, and changes of states.
There is an operational change when the wheels leave the ground. The associated sensors would send that data to the CCS. What was sent? Maybe the CCS read Hydraulic L + Hydraulic R + Hydraulic C = incorrect or fail, which would trigger deployment of the RAT. What would the electrical and control system do then? More importantly what exactly did all the systems do on this aircraft following such an event.
Was there a problem with the fluid in the hydraulics? Does hydraulic fluid ever 'go off' in very hot conditions. Or maybe there wasn't as much fluid in there than there should have been? How would hydraulics systems be compromised if indeed that was the case.
All speculation - but forensic system analysis is a bit like that

Originally Posted by lighttwin2

There are a few comments along the lines of "it is incredibly unlikely that..." this is selection bias in reverse. Something incredibly unlikely has happened, and it's contained in this sample set.

To summarise some known facts about the TCMA system:

1) TCMA will shut down an engine if:

• It believes via multiple redundant sensors indicate the aircraft is on the ground
• It detects engine power in excess of that set by the thrust levers - subject to a margin to account for engine performance variation - that is determined to be a runaway condition

2) In 2019 an ANA pilot was able to confuse the TCMA by rapidly moving the thrust levers into reverse, to forward and back into reverse again. This caused both engines to shutdown.

3) Since then the TCMA should have been updated/fixed (and indeed the software will have been updated by SB since the a/c was delivered, to detect a wider range of runaway conditions)

And speculation:

4) It may be possible - given the close timings - that a TCMA activation occurred as the a/c was leaving the ground, with kinetic energy and spool down time getting the a/c from the ground to its peak height

In the recent BA LGW incident the PF reduced thrust to idle at V1, then added thrust back, then committed to a RTO. I wonder if something similar could have occurred:

• In error, PF reduces power to idle at a speed approaching V1
• Engines begin reducing power, but n1 reduces more slowly than the TCMA system is expecting (perhaps because the TCMA margin is calculated when the a/c is stationary, but at 170kt a turbofan will spool down more slowly due to the ram air / windmill effect)
• TCMA detects a runaway condition - while a/c is on the ground - and cuts off fuel via the relay circuit
• PF decides to commit to takeoff and rotates, not knowing that TCMA has already activated
• 10-15s after rotation, n1 has now dropped below minimums for electrical generation. Electrics fail, final transponder signal is sent, and RAT is deployed

Obviously this should not be possible, and there are other possibilities.

Originally Posted by Stivo

Am I understanding that you are saying that the noise on the video identified as a RAT has a Doppler shift that matches plausible values for height and speed? That seems pretty conclusive to me that it is a RAT.

Originally Posted by Pelican

Trying to keep an open mind, but\x85.

Is no one surprised the lone survivor remembers a bang just before impact, and other things like apparently emergency lights, but has not mentioned the power going from takeoff power to nothing. Even the power change at thrust reduction altitude is often very noticeable in the cabin, so it surprises me nothing about the noise (and startle/panic) of full-power to no-power has been mentioned. I think we are getting into absurd scenarios trying to make the scenario of a simultaneous double engine failure just after liftoff fit, based on perhaps not the best evidence.

Originally Posted by JG1

A little bit tangential here, thinking about this Mayday call (the exact contents of which haven't been verified, but have been variously reported as "no power", or "lost power" ) , if in front of you on the PFD, in large red letters, you have the words ENG FAIL, why would you say, "no power"? Seems a bit strange. Why not say "engine failure" or "no thrust"?

Could it be that "No power" may have meant the whole cockpit went dark? ie. A total electrical failure or huge short (survivor's bang) initiating RAT deployment and apu autostart. Doesn't explain loss of thrust explicitly but if there was a massive electrical issue, and critical data was lost (thinking air/ground switch position and other fundamentals), would dual engine shutdown be a possibility? Simultaneous FADEC failure? Exceptionally remote possibility perhaps, but by definition these accidents are exceptionally remote. If the RAT deployed we know there was definitely an electrical issue - how bad was it, though? Thinking about the possibility of an electrical failure causing an engine (and instrumentation) failure rather than the other way around. Over to the experts on this.

Originally Posted by LTC8K6

The 787 is reliant on good electrical power and plenty of it and we have signs of electrical system failures on this 787. We have a RAT deployed. We have data loss. We have previous flight reports of electrical problems in the cabin. We have a survivor report of lights flickering and a bang - which could well be the RAT deploying.