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

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.

If they retract flaps their speed does not necessarily increase.

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.

I've only heard RATs in the wind tunnel, and the sound does not jump out at me as being a RAT.

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.

With all due respect, based on the videos released so far, it appears the aircraft had no thrust\x97even without considering the sound of a deployed RAT. I could be mistaken, of course, but a flap/gear configuration error doesn\x92t strike me as a likely cause.

In summary,

Flaps were extended, possibly flaps 5 or 15. Looks like it in the video and clearly shown post crash.

Aircraft reached a height of just over 100\x92 AGL (possibly 200\x92 if you compare wingspan to height in videos)

RAT was deployed. Seen on videos and heard conclusively.

Aircraft rotated at \x91usual\x92 spot. Comparing FR24 data from previous flights over the past week.

Aircraft took off at \x91usual\x92 speed. Comparing other flights.

FR24 data stopped being sent shortly after take off. Possibly indicating electrical fault.

Green and white flashing light reported by survivor. Possibly indicating electrical fault.

Gear bogies were at unusual angle indicating Gear selected up and then interrupted.

No smoke or flames to indicate bird strike. (Edit - still debate about this in the video above where the aircraft is behind a building)

No rudder input to indicate single engine failure.


All speculation but hopefully a pretty balanced summary from the thread so far. It would be great if there was more focus now on what might have caused above rather than talking flaps, birds, 625\x92, etc.

Misselection of flap, erroneous TO Performance data, dust = overrun, bird strikes\x85.all unlikely as none fit the evidence; the engines were very quiet.

The clearest bit of evidence is the RAT deployment. As someone else pointed out gear bogey position indicates Gear UP cycle had commenced.
So the most evidenced sequence of events was rotation, positive rate = gear Up; \x85.catastrophic Power Loss. Flickering cabin emergency lights and Loud bang reported by survivor (was this heard RAT deployment or another system?).

The 787 has some unique electrical/mechanical and air systems. Previous flight had issues (reported by passengers).

So the root cause of the Power failure must be down to when either the 787 gets airborne (weight on wheels switch) or when Gear selected Up. I wonder if any 787 drivers could elaborate on what electric/hydraulic/air systems are affected at the very point of wheels up or gear up ?
I\x92m wondering if the electrically powered cabin pressurisation system is affected at wheels up?

In the take off video I think there is a subtle yaw to the right at lift off (the moment it begins being obscured by the building in the foreground). There is then a massive blast of dust on the airfield on the left side of the aircraft as it lifts off. Later video audio suggests the engines were not at full power ( or even operating - just wind noise) and that the RAT was whirring. It also shows the fuselage wheel bogies were tilted forward - so wheels up has commenced - but the gear doors are not open.

Possible sequence: right engine failure at rotation, firewalling of left engine, lift off and positive rate, gear up lever activated, wheels tilt forward, left engine failure, RAT deployed, insufficient hydraulics to Open gear doors to complete gear up sequence, ongoing dual engine failure?

The speed at which there was a complete loss of thrust and electrical power degrading to the point of flickering lights and RAT deployment suggests to me an actual engine shutdown rather than anything linked to auto thrust or fuel contamination. There are not many things which can cause an engine to shut down: LP valves, FADEC incl TCMA, crew action\x85

We're all shouting each other down with two main different theories on why the aircraft lost lift so shortly after takeoff.

1) Incorrect flap retraction causing the aircraft to lose lift and unable to recover the energy in time. (Not unheard of and plenty of reports where this has happened - albeit usually not to a crash).

2) Loss of engine thrust backed up two potential pieces of evidence that back up the RAT was deployed (apparent RAT sound, potential RAT seen on low res video).

It is impossible to know which of these is the case. Considering this summary of memory items is there the potential for a combination of both theories to have taken place?

Inadvertant flap retraction by PNF leading the PF to sense a sink and loss of lift. Pushes the thrust levers forward to the firewall and still the aircraft sinks. PF looking through the HUD and so very much 'outside focused' and doesn't realise that PNF has instead moved the flaps. PF defaults to memory items for loss of thrust on both engines before PNF can realise or communicate to PF what they've done, start switches are cut off which drops the RAT and from that point they're only heading one way. This would satisfy the strongly held belief that the RAT was extended, whilst also following the more likely initial cause of an action slip by PNF starting the sequence, rather than a dual engine failure.

Gear is actuated from Centre system hydraulics which is pressurised by two AC electric pumps not the engines.

Neurotypically an error in an automatic action will occur when the routine that encompasses that action is changed. Hence babies being left in back seats of cars, and probably a factor for the sterile flight deck rule. Any reason to think that might have been in play here?

I agree it is helpful to seek a consensus on some of these matters.

The most productive responses would be along the lines of:-
(1) I too have read all previous posts and agree that your summary reflects the current consensus,
(2) I too have read all previous posts and agree your summary reflects the consensus HOWEVER I challenge that consensus because... [ [i]EITHER (a) reference to previous post that merits greater credence, OR (b) new evidence supplied],
(3) I too have read all previous posts but I do NOT agree your summary reflects the consensus [explanation required].

It is not necessary for everyone who thinks (1) to say it (although some initial feedback would be useful!). However, if any of the more experienced and informed PPRuNers are thinking either (2) or (3) then it would be instructive to hear that.

FWIW, yours strikes me as a reasonable summary of the best consensus I have been able to discern (as of ~30 minutes ago). There are multiple caveats to each line item, but I presume you've deliberately left those out for the sake of readability, so I'll do the same!

The only comments I would add are:-

- It's a stretch to say the RAT is seen or heard "conclusively". Doubts have been expressed about the video quality and there are dissenting views regarding the audio. If a few more people were able to wade in on the audio point in particular, this could be very beneficial in moving the discussion forward because the presence or otherwise of the RAT is significant to several competing theories.

- On the subject of audio, I am surprised there has not been more discussion regarding engine noise. In the primary eye witness video the (alleged) RAT can be heard distinctly, as can the sounds of distant impact. If the engines were working as expected when overflying the camera and then flying directly away from it, do we really not think the engine noise would be more conclusive, i.e. louder (notwithstanding quiet engines and derated takeoffs)?

Whichever way readers are leaning in the flaps versus power loss debate, surely these two points are pivotal, and we have actual evidence available to discuss?

- Gear bogies: I'm not sure a consensus has yet been reached regarding the angle of the bogies. (I am not personally qualified to comment on this - I am purely saying I don't see a clear consensus just yet among those who are)

- Mayday call: I don't recall seeing a confirmed source for the widely reported mayday. Others have brought this up in the thread but nobody appears to be able to confirm one way or the other. If accurate, its contents are informative. Am I right to presume that you have left it out of your summary due to a lack of confirmation?

The only other way the RAT can be deployed is manually, using the p/b on the overhead panel. Almost certainly this is a highly unlikely action given time & distractions. But it is one possibility that needs examination and elimination in the data.

Actually not true. Remember the 737 with iced up itt probes that hit the Washington bridge?
a simple \x93yugga\x94 on the power levers would have prevented disaster.

probably irrelevant to this topic however