Posts about: "Flap Retraction" [Posts: 66 Pages: 4]

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.

that\x92s why the switches and levers are designed like this. The gear lever is round like a wheel and the flap lever is, well flap shaped. Mixing up switches was/is common. Happened to me in my training pulled the mixture full out instead of carb heat on my approach. Immediately realised the change in the engine and pushed it back in before it cut out completely and engine started up again. Change of underwear required.

And another: https://www.gov.uk/aaib-reports/aaib...319-111-g-ezew

In an Airbus the flap lever is even further away from the gear lever than in any Boeing, yet still it happened! Action slips are just that and to blindy say that moving the flaps before gear is impossible, just because they are in a different location is incredibly naive. Next time you pour orange juice in your tea because you were thinking about something else and grabbed the wrong carton will you decry it impossible?

To be as crystal clear: I am not saying this is how it happened, but it could be. Just as other things could be.

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 still don\x92t understand the flap retraction theory

It happens- in every airline in the world, ask any of their training/FDM departments. There are reported incidents of it from almost
Every major airline I can think of. Humans are incredibly fallible, I\x92ve spoken to a captain who did this on the 737 back in the day (now flies Airbus) and on that day he caught himself. He said in the debrief after the flight he could not explain why he did it, absolutely no clue.

The issue I have is why one of the most modern aircraft in the world, a thoroughly 21st century clean sheet design with every protection under the sun would not have the adequate protections or performance to deal with this scenario. Surely the 787 has high AOA and low speed protections- those engines should\x92ve been screaming at TOGA LK (or the Boeing equivalent) and the pitch should have been limited regardless of the weight, density altitude etc

Airlines and manufacturers will always try and blame the pilots but I would be truly shocked to learn a FBW aircraft (Boeing or not) designed this century could get itself into such a catastrophic state so innocently. We KNOW many crashes have been prevented by Airbus FBW protections (a few Wizz examples come to mind

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.

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?

It's tempting to think that, however one may also have made the case 'why doesn't Boeing install a system that prevents the nose getting too high on the 737 MAX? Then they won't have to retrain crews on handling differences'. We know how that worked out.

When designing anything you need to account for unintended consequences and the possibilities for that system adversely affecting safety if it were to malfunction. If you introduced a system designed to prevent flap retraction 20 to 30s after liftoff, what if failure in a channel of that system then prevents flap retraction required to achieve a MACG with critical terrain on departure. We could 'why don't they do this / why don't they do that' until eventually we end up with not flying at all.

On your point of integrated scales, there is a far easier way to cross check actual aicraft weight with calculated weight: a computer that cross references acceleration data on the takeoff run with known values from lookup tables based on specific environmental conditions and engine thrust settings. If you're not accelerating at a normal rate expected for the calculated thrust and weight a warning can be triggered. This was a recommendation echoed by the AAIB following the incident with a Jet2 aircraft getting airborne at only 70% thrust. I believe Airbus and Boeing are looking into the potential implementation of such a safety system.

Exactly like the action of lifting the flap lever out of detent before moving it. What is significantly different is that you would have to do it twice. It is that which makes it improbable unless intentional.

This I believe is an option to retrofit. Can\x92t recall the supplier, Honeywell perhaps, not sure on the 737-MAX and whether it has anything fitted as standard.. Anyway the more cost effective option (for NG operators) is to amend SOPs where appropriate. However the U.K. CAA do apparently intend on creating a working group regarding such events. See also the TUI event at BRS.

https://asn.flightsafety.org/wikibase/388602

https://simpleflying.com/aaib-report...f-runway-10ft/

It\x92s worth noting that the acceleration rate was exceptionally low in the TUI event based on the average for that airport. I refer you to my initial post on this thread, it\x92s a risk that there is no config warning horn (to my knowledge) on the B737-800 that will alert the crew, upon selection of TOGA, that the performance solution entered into the FMC does not agree with the actual config. In the case of flap setting, it will only alert if a non standard take-off flap setting is selected. If in the unlikely event TOGA is not pressed at all then\x85..

Airbus have added something of an FWC to their 321NEO aircraft that will alert crew to this - something I\x92d heard from bus mates but wasn\x92t 100% certain on so thanks to those on here that confirmed.

Sorry for further thread derailment, however felt it might be of interest. 787 rated crew on this thread suggest this would form part of the electronic checklist on the aircraft so in the case of the event at hand a red herring.

Why the need to make the two theories fit in such a convoluted manner? Inadvertent flap retraction was theorised because people assumed that was most likely to have caused the loss of lift - hardly anyone believed dual engine failure was possible. Now we know that the loss of lift was indeed almost certainly caused by a loss of engine power, why all these awkward attempts to reverse engineer it to still fit the flap retraction theory? People need to realise they are only trying to make the flap retraction theory fit because of cognitive biases. If we had all been told immediately, there was dual power loss and the RAT deployed, no-one would even be considering flaps. Its confirmation bias of past assumptions, that's all.

As has been said many times as well, the landing gear retraction process appears to start as the bogies tilt, and then suddenly stops. Which rather suggests they did pull the gear lever. Based on the videos and the amount of speed the plane lost in the very brief sequence ovents, I'd say that the plane lost power a lot earlier than it would have in your theory.

How do we \x91know\x92 that, exactly?

Good summary, I'd just say the thrust levers definitely weren't firewalled. The plane lost a huge amount of speed by impact. This single fact should be enough to end the flap retraction theory. It lost a huge amount of speed while descending - now what might cause that? The gear also begin the retraction process (bogies tilting). The obsession with flaps when there isn't a single piece of evidence for it is very odd. (not suggesting you are guilty of it btw).

The requirement to lift the cutoff switch out of the detent before moving it is an important point. However, those switches are close together and unless the the detent requires significant force I suggest that they could be operated together with one hand if that was an intentional action.

Out of interest, are you using ground speed or airspeed?

Even if airspeed increased in the event that flap was inadvertently retracted, the critical angle of attack would decrease. To counteract this, unless airspeed increased (I.e with sufficient thrust perhaps, like in a windshear escape manoeuvre) relevant to the pitch attitude, the only way to generate sufficient lift would be to create enough airflow over the wings, or more simply in this scenario to lower the nose, but this doesn\x92t appear to have occurred in this event*

Or am I missing something?

*accepting the poor evidence available to us, there is no evidence of flap retraction leading to this event. Having since seen Magplug assessment I\x92m tending towards that theory in the absence of official findings.

Even if they selected the flaps to the next higher flap position on a flight to London the 787 would have been able to power out of it. The deceleration rate and aircraft attitude don\x92t suggest to me an inadvertent flap retraction. I have done this exercise in the 767-300ER and it\x92s almost a non event unless extremely heavy.

On item 1, the TCMA issue should have been fixed, it does fit the sort of issue that occurred here. TDRACER can talk to that, and has done in 2019 and again in post 792. As to flap auto retraction, the B787 like all Boeings has a gated flap lever, and the flaps are only able to move independent of the lever by flap load relief. That would not have caused a loss of thrust, and in this case it is evident that the event is a thrust loss not a CL loss.

On item 2, the video shows no asymmetry at any time, so there is only a symmetric failure of the engines possible. Back on a B747 classic, you could chop all 4 engines at the same time with one hand, on a B737, also, not so much on a B777 or B787. I would doubt that anyone used two hands to cut the fuel at screen height. Note, there was a B744 that lost one engine in cruise when a clip board fell off the coaming. Didn't happen twice, and it only happened to one engine.


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Neila83 is correct, the gear tilt pre retraction is rear wheels low, and at the commencement of the selection of the retraction cycle (generally), the first thing that happens is the inboard MLG doors start to open below the wheel well and then the bogie is driven to front wheels low. (There is also an option that the inboard gear doors start to open early as a result of WOW sensing to improve the SSL climb limit). [my bad, for the B788 Capt Bloggs informs us the gear door sequence is after the tilt, not before, the B789 has the before tilt, the option for the door open at rotate is separate]

The inboard doors do not appear to have opened in this case, yet, the gear is forward wheels down. This appears to be out of sequence. TD may have better knowledge on the options that exist with the B788, but this is not looking good at this time.

There is enough in the way of anomalies here to end up with regulatory action, and airlines themselves should/will be starting to pore over their systems and decide if they are comfortable with the airworthiness of the aircraft at this moment. A latent single point of failure is not a comfortable place to be. Inhibiting TCMA might be a good interim option, that system could have been negated by having the ATR ARM switches....(Both)... ARM deferred to the before takeoff checks. The EAFR recovery should result in action within the next 24-48 hours. Boeing needs to be getting their tiger teams warmed up, they can ill afford to have a latent system fault discovered that is not immediately responded to, and the general corporate response of "blame the pilots" is not likely to win any future orders.

I think we are about to have some really busy days for the OEM.


Not sure that Neila83 is that far off the mark at all.

Gear possibly not selected up due to startle effect after a major event.

Bird strike unlikely to knock out both engines unless there is a flock of them, you might get a single bird into one engine but the odds of two birds each hitting separate engines are pretty long.

Aircraft often yaw slightly after takeoff, particularly with a crosswind which may be stronger in the air than on the ground.

Air India have had issues with pilot training and standards, reports not too long ago of Indian flight schools selling logbook hours which didn't involve any time in an aircraft.

Numerous reports of cabin maintenance issues with Air India, if they can't fix the seats and IFE possibly they can't fix other things.

These days, high resolution cameras aren't prohibitively expensive and installing a few at airports would be better than mobile phone footage.

Wouldn't an incorrect altitude setting pitch the nose downwards and keep power on for the aircraft to accelerate ?

Boeing philosophy is for the pilot to have ultimate control of the aircraft, Airbus try to protect the aircraft from pilot error. Inadvertent flap retraction on an Airbus will result in the slats remaining out and TOGA, which whilst not a guarantee, has saved a few necks.

Possible issue with the particular type of engines fitted to that aircraft, even worse would be an aircraft issue which would have had the same result regardless of the engine manufacturer.

The B787 has enough OEBs on it to fill up a small binder if printed out, some of which state that the issue is known about and the company is working on it.

Hopefully, given the time that the aircraft has been in service, it won't be a systemic problem suddenly coming to light in the way MCAS did on the B737 MAX relatively soon after EIS.

RAT out? I think not. Sounds like aorflow changes as flaps retracted.
Flap lever quadrant has a gate preventing quick lever movement past F1 position.
So if flap lever selected on first movement, the lever goes to F1 position, where only the trailing edge flaps retracted whereas the slats remained at takeoff setting.
Hoping against hope it wasn’t a brain fart!😖

The flight part is nothing like you would see with the flaps retracted from 5 to 1 and the aircraft would have been able to recover and fly out of that at their likely weight.