Posts about: "RAT (Deployment)" [Posts: 361 Pages: 19]

If the fuel was cut off, how long would it take until the engines spooled down? How long would it take, given wind-milling etc, for that to result in a loss of power? I'd love to see a timeline of the flight with the fuel being cut off that is remotely compatible with the events we saw, because I don't think it's possible.

I had wondered about TCMA being involved. Software is extremely complex and there have
been examples in the past where it does something it wasn't supposed to do, causing an incident.

It looks like you recall correctly. This skybrary PDF document "Fade Free Memory" describes the EAFR

https://skybrary.aero/sites/default/...shelf/2955.pdf

I quote from it:
That seems to indicate that as long as the forward EAFR is powered, the datastream from the cockpit area microphone will be available to both EAFRs (assuming the network to the aft EAFR is available and working).

The whole document is worth reading to glean more details.

Related question: I asked earlier at what speed the 787's RAT becomes effective in providing hydraulic power. Is it possible that by the time the RAT deployed, the aircraft had lost airspeed to the point that it would have struggled to produce an adequate amount of pressure? Taking the Gimli Glider incident as an example, my understanding (could be wrong, this was from a magazine article) is that as they bled off speed to land, they ended up short enough of hydraulic power that they started to experience control difficulties, with the plane responding fairly sluggishly. If that's the case and this poor crew was going through something similar, it might explain why they seem to do very little about their situation.

Presumably a dual engine shutdown under TMCA (i.e. similar to the ANA incident) would cause the RAT to deploy.

Obviously difficult to envisage what could cause an TMCA activation on both engines simultaneously given the safeguards in place (weight on wheels etc). However maybe the time delay from an erroneous TMCA activation on the runway/at rotation would lead to a loss of power 10 seconds later.

Firstly, I don\x92t think an inadvertent selection of flaps up caused this accident. I think it\x92s a red herring that seemed plausible initially but it is not consistent with the RAT being deployed, and the evidence for the RAT is strong.

To answer your broader question though, how could such an error happen? It happens because us simple humans learn how to do actions to the point where we don\x92t have to think about them anymore. This allows us to effectively automate routine tasks and save our brains for more novel tasks. The problem arises when we trigger the wrong automatic action in response to a cue. You ask for gear up, I know I need to select the gear up, I know where the gear handle is and what it looks and feels like, yet something goes wrong in the wiring of my body and instead, the flap-up automatic action is run. It\x92s run before I have consciously thought about it.

Sound far fetched? Well it has happened numerous times. I\x92ve seen someone do exactly that, select the flap instead of the gear, and there are incident reports publicly available. All modern passenger jets have a similar layout of the flap lever and the gear lever with the gear looking like a wheel and the flap looking like a wing, yet this error can still happen.

Have you ever gone to put something in the fridge that should\x92ve been put in the cupboard? I\x92d bet that most people have made that weird error at some point in their lives, and yet the fridge doesn\x92t look like the cupboard and they\x92re nowhere near each other.

The problem with the flap handle/gear handle mix-up theory is that it would appear in the original video that the gear up sequence has started based on the main gear leading axle pointing downwards, which is the first thing that happens (hydraulically) when the gear handle is moved.

Retired engineer here.
I have looked at the electrical systems on the B787 and this is my source. Book 1 Introduction to B787 Avionic/Electrical. Tried to post the URL but was unable to do so as I haven't made many posts.
I wonder if there may have been some kind of complex fault in the electrical system that day. The incoming flight passengers reported faults with the air conditioning and IFE. The electrical power system block diagram is on p. 84 mentioning engine generated power and the RAT which, if deployed, feeds a backup power bus. There is a power limit on the RAT system of 10kVA which probably isn't enough to retract the undercarriage (correct me if I am wrong). The main electrical system is 235V ac from the engines which is converted to DC using ATRU units (Auto Transformer Rectifier Unit) - see p. 95. These systems get very hot so there is a liquid cooling system called PECS. If there were malfunctions in ATRU units that may explain the air conditioning issues on the incoming leg. So, what exactly triggered the deployment of the RAT?. I'd be looking at the whole electrical network and not just the engine generation systems. The emergency lighting system (p. 146) is called WELS (Wireless Emergency Lighting System). The survivor mentioned that was flickering. Power/control systems cutting in and out. Those lights would be battery backed and would stay illuminated if the primary power/control permanently ceased. Just a few thoughts for consideration.

This was handled in this PPrune thread:
ANA 787 Engines shutdown during landing
and in AvHerald:
https://avherald.com/h?article=4c2fe53a&opt=0

Just to clarify one point: the ANA B787 was powered with RR Trent 1000 engines while the Air India had GEnx-1B67 engines.
So, the Air India thrust failure may still have its source in the TCMA system, however, if it's the case, the logical path must be somewhat different than for the thrust reversers of the ANA airplane.

Just remembered this video of a787 with its RAT deployed. You can certainly hear it. A lot of people said you could hear it in the AI video but I couldn\x92t.

A long while ago I posted on the Rumour thread about a ban on drinks on the flight deck sent to a BA, A350 mid Atlantic. It was prompted by 2 separate instances of uncommanded unrecoverable engine shut downs due to drink spills across the fuel cut off switches. It was widely mocked by the professional pilots on here until proven to be absolutely factually correct. If we are into speculation why not a drink left on the flight deck tips on aircraft pitch up and spills across both fuel cut-switches. Just sayin

Hutch

Jump to 1:48 in this video (if the link doesn't automatically put you there): You can't hear that RAT sound at the very beginning of the flypast?

I'll tell you what you can absolutely hear in that video as well: the engines. Now go to the crash video and compare.

I'm pretty convinced that everyone is watching different videos, which wouldn't surprise me in the least given how much images and footage can get mangled from being downloaded/re-uploaded to different services. Personally I've seen at least two different videos (and slightly different variants of each): one that's a direct recording of the aircraft and one that's a recording of a phone playing a recording of the aircraft. The buzz of a propeller was quite audible in the former but not in the latter, and the engines are notably quiet compared to any 787 takeoff I've ever been close to.

I do think that at this point people are working backwards from the cause being retracting the flaps, rather than working forwards from the evidence towards an explanation. If everything else was as it should be apart from flaps being retracted instead of gear, you'd at the very least expect the aircraft to reach a higher speed than is suggested by how little distance there is between the end of the runway and the crash site. Coupled with the apparently parabolic trajectory seen in the airport CCTV video, the crew (allegedly) reporting engine problems on the radio, the surviving passenger testifying about flickering cabin lights, the plausible deployment of the RAT, the fact that the ADS-B data cuts out well before impact...surely at some point one must consider a lack of thrust, no matter how improbable. Recognising the what doesn't need a full thesis on the how .

I wonder if (given all the facts and rumours about the situation so far) the flaps would be so high on everyone's minds if they weren't already a hot topic from the initial, largely baseless speculation that they somehow took off with flaps retracted.

I agree with your thinking, suggest that others read and further discuss on that track.

If this is not the RAT spinning then I will eat my shoes....
Something else, there have been discussion about not much engine noise heard. Causes could have been poor mic, a lot of background noises etc. What stands out to me listening to this video is how clearly we can hear the crash itself, even from behind the buildings, but there is absolutely none/zero/zilch/nada engine noise to be heard whatsoever, not much other background noise either for that matter.
This non-aviation related engineer is now convinced that the RAT was out spinning and the engines was either shut down/flamed out/whatever or alternatively at not much more than idle power setting. Considering the deployed RAT I would go for shut down engines.
Now, what the cause for all this might be I have not much idea about, except possibly some very significant electrical system malfunction.

SLF here, retired physicist, but with much engineering (esp. systems engineering) background and considerable interest/experience in fault-finding in complex (not aircraft) systems.

I think it is helpful here to work through some possible failure scenarios in some detail. You could usefully partition these into two separate groups: “RAT was deployed” and “RAT was not deployed.” I’ll mostly follow the former here.

\xb7 By following this path, I think we can exclude incorrect flaps setting or premature flap retraction as the primary cause of the crash. It’s difficult to see how improper use of the flaps would be correlated with RAT deployment. Everything in this case points to a loss of engine thrust.

\xb7 The first question is, why did the RAT deploy? As I understand it, manual deployment by a pilot is possible, or automatic deployment caused by detection of major electrical or engine failures. I haven’t found an authoritative, detailed discussion of this, or about the time to deployment, which is relevant here as there is so little time involved.

\xb7 According to tdracer , if the primary issue was a major electrical failure, that should not have caused any engine rollback. Thus, absent pull back of the throttles (which surely would have been corrected by the pilots), there should not have been a loss of thrust.

\xb7 Thus we are left with engine rollback as the likely underlying problem. Absent other issues, a single engine rollback should not have been a major problem, so dual rollback, unlikely as it might be, seems a reasonable conclusion.

\xb7 This is consistent with the reported mayday call, although that report needs confirmation.

\xb7 It is difficult to understand a dual engine rollback. Various causes have been suggested but ruled “unlikely” here. However, it is not possible to rule out a unicorn event, like the dual engine rollback experienced by BA 38. Leaving aside the cause, it is useful to look at the consequences.

\xb7 There would have been a major loss of electrical power (apart from battery backup), assuming the APU was not running. I don’t know if is possible the APU might be used at takeoff (e,g., to unload the main engines), or if any evidence from the tail photo at the crash site provides a meaningful indication (e.g., intake door status).

\xb7 Are there other indications of loss of electrical power? The reported statements of the surviving passenger may have some relevance, but I would want to see the results of an interview by crash investigators.

\xb7 What about the loss of Flight Aware ADS-B data shortly after takeoff? There have been a few mentions of this, but not much discussion. Could this indicate loss of electrical power?



I hope this is of some use. I’m happy to defer to professionals or others here for better information/analysis.

The nose gear angle suggest that the "gear-up" was selected and a dual engine failure happened at the same time, with the hydraulics failing and possible RAT deployment.. The APU was not running and everything, except the flight recorders, might be powered down and restarted at a very low altitude.

Very scary.

An early number 787 (in the first twenty four), had to make an emergency landing at New Orleans on a Houston to Newark flight. At this point, re Air India, with the RAT screaming in the original video, an electrical issue of some magnitude is at the fore. Each engine has two generated power unit (GPU). Total of four (NOT ground power unit). If one of these goes offline, the system adjusts. If an engine quits, two are gone, and the remaining two supply e power.
Powering up all four at once can cause a shutdown of all generated power. The question becomes which failed first, the engines or the electrics. The RAT deployment signals either both engines shutting down, or four GPUs. I think negative on Pilot Error.

Whatever the direct cause, this amount of grief is impossible to imagine. God have mercy

Yes, this is the odd part - from the videos it didn't look like there was any attempt to put the nose down for best glide, and even the pitch up (if presumably from fear) was not very pronounced. It basically came down in the same attitude as during the takeoff. That has me wondering if they even had any controls at all. Very low probability, true, but then both engines out is also a low probability event. 'RAT Push and hold 1 second' seems to be a dual-engine fail memory item on a 787, so both engines out would explain the loss of thrust and the RAT deployment.

The lack of obvious debris/smoke during takeoff might indicate it was something other than a birdstrike, and combined with the loss of adsb (per FR24) right over the runway threshold at 70ft agl, maybe it is indicative of something else causing the simultaneous loss of thrust.