Posts by user "Tu.114" [Posts: 11 Total up-votes: 0 Pages: 1]

The video seems to show the aircraft descending from a few 100ft altitude to an impact. The landing gear appears down, flaps are harder to make out.

How does a 787 react to low speed? What are the protections on this type?

So what is known at the moment?

- The flight crew consisted of an experienced Captain and a First Officer with a little more than 1000 hours. Whether or not this flight was a training event appears not yet determined.

- The aircraft departed from Ahmedabad, using full length of the runway, lifting off at an appropriate distance from the departure end and reaching an altitude of less than 1000ft before descending again to an impact. It therefore got out of ground effect. Also, the power selected for takeoff was sufficient to get the aircraft airborne within the constraints of the field.

- The landing gear was left down much longer than usual and remained so for the whole duration of the flight.

- Flaps appear to have been extended normally to a setting not triggering any pre-takeoff configuration warning. On the 787, extended TE flaps are not as obviously visible as on other types, especially with low quality pictures, but a gap between the flaps and the wing proper was visible, showing a glimpse of the engine nacelle through it.

- Whether or not the RAT was out appears not entirely clear, although there are strong indicators of it being deployed. If this is confirmed, this seems to point to a major engine or electric issue.

- Engine noise is surprisingly low on the available videos, either drowned out by environnmental noise (the 787 is not a noisy bird) or due to lack of power produced.

- Descent was at a very high AOA and appears not intentional. The crew did not decide to push the nose down.

- The aircraft appears to have been structurally intact with nothing issuing from it. No debris, smoke, fumes or liquids were in trail, no parts were observed to have been lost or dropped.

- There seems to have been a mayday call from the aircraft, possibly indicating power issues.


The crew seems to have found no reason to abort the takeoff before V1. Whatever befell them must have struck past that speed and given them cause not to retract the landing gear. Whether the lever was not moved or the systems did not react to it is not determined yet.

The aircraft had enough energy to climb to about 600, in any case less than 1000ft altitude. Ahmedabad seems not to call for a specific NADP, but whether it was NADP1, 2, A or B that was flown, it is fairly safe to assume that its normal regime would have been takeoff power and takeoff flap settings at that time.

Multiple other aircraft departed from or arrived at Ahmedabad before the accident, of which at least one must in all probability have taken onboard the fuel from the local bowsers in substantial amounts and used it without troubles, or else there would have been other flights in trouble due to this.

I am awaiting the preliminary report from the authorities and the readout of the data recorders with much interest.

This is likely some animal, either a dead horse or a red herring, your choice.


The power they selected for takeoff was sufficient to get them airborne. Whatever noise abatement protocol was chosen, the power will not be reduced before 1000ft AAL, so whatever N1/EPR (I do not know what indication the engines on the accident plane used) got them out of the runway was still selected.

If lack of power was an issue, this problem started after V1 and likely after liftoff. One working engine would have sufficed to get them out of the runway after V1 and to a relanding, this is a regulatory requirement. That the weight, temperature, air density, obstacle situation and so on allows for this will have been confirmed during the takeoff data calculation.

Here is another video.


At 0:21 to 0:22, there appears to be an odd yellow flash around the #1 engine. This may of course also be due to the rather bad, filmed-off-a-screen video, but it occurs after liftoff and around a time when gear retraction would be appropriate.



Edit: here is another video showing the same scene in slightly better quality. The same flash is visible around 0:46.

This does not necessarily mean anything, of course, and it may as well be some reflection of the sun, but it appears to be about at the time a total power loss would have brought the known results.

Something rather relevant has not yet been shown on this thread: a performance calculation.

Could somebody with access to a 787 performance calculator please show realistic figures for this type out of Ahmedabads runway 23?

Weather at the time of the accident:

VAAH 120830Z 24003KT 6000 NSC 37/17 Q1000 NOSIG=
VAAH 120800Z 25007KT 6000 NSC 37/16 Q1001 NOSIG=

With 240 souls on board, a payload of 20-22 tons might be a ballpark figure, and a fuel load of about 50 tons was claimed as realistic in earlier posts.

An appropriate flap setting, a flex temperature, V1, Vr, V2, flap retraction and green dot speed (or its Boeing equivalent), a climb gradient after departure, and some distances might be of interest, I\xb4d think.

If there was a loss of power, it happened after V1. Normally, at V1, all hands should be removed from the thrust levers until, type dependent, selection of climb thrust, which normally takes place not below 1000\xb4 above aerodrome level. An altitude the flight never managed to achieve. If some flight crew members seat was to slide back unintentionally, there are handles in the flight deck that one will instinctively reach for, no need to grab the thrust levers of all things.

Even if the levers may have been inadvertently pulled to idle, it would have taken one single energic adjustment to slam them to maximum thrust position (whatever it is called on the 787), for which there was some time during the brief flight. And two idling engines should not result in anything triggering the RAT release or APU auto start.

Of course, stranger things have happened, but I\xb4d consider this scenario not plausible.

The electrical failure is rather a chicken-egg question.

Not knowing the 787, I\xb4d find it extremely hard to believe that a massive electrical failure would kill the engines. I gather from this thread that the landing gear retraction is driven by the electrically-powered Center hydraulic system. Retracting the gear is hard work for the system and it will put a strain on the two pumps and their supplying electric circuits, and the time of the alleged total power loss would seem to be in the vicinity of the suitable time to retract the gear.

But if there was some freak epidemic failure this inflicted upon the aircraft electrics, it is hard to imagine that this would affect both engines. There are still the autonomous FADEC governing them that run on their own internal generators (with a small external power source from the main systems, should the permanent magnet alternators fail) and do everything they can to keep the engine alive. As long as there is fuel flowing into the feed pipes, the engine should be kept running by the FADECs, and that this does not require the large tank pumps at low altitudes has been established in this thread.

Consequently, I\xb4d deem it plausible that the alleged power failure must have been a consequence of whatever happened to the engines. After all, the engines drive the available generators at this stage of flight, the APU with its additional generators is apparently not run for takeoff on the 787. I find it logically much easier to wrap my head around a situation in which an engine failure takes along the generators than one in which a massive, epidemic electric breakdown kills the engines.

A question has crossed my mind today that may or may not have any relevance to the accident and for which I have not found an answer on here.

TCMA has been discussed here for a while, it will in a nutshell shut down an uncontrollable engine on the ground. Is there any additional lockout triggered if one of the installed engines is already not running, be it due to a TCMA emergency shutdown or due to some other reason? Or does TCMA have the authority to shut down any engine, whatever the operating state of the other engines may be, as long as the condition "not flying" is satisfied?

Lonewolf_50,
thank You for the response. I admit to a little (possibly over-)simplification.

Having read the brief explanation by the man himself here , I note that that system appears strongly protected against inflight activation, but there is no word on a lockout in case it has been triggered on one engine already.

My thought comes from remembering the DH8, in which the autofeather system (that by another mechanism and due to different reasons than TCMA removes an engines capability to provide thrust and therefore appears to me slightly comparable in this aspect) had a system that ensured that once one propeller had been autofeathered, the system was disabled and did not attack the other engine. The risk caused by an inadvertent forced feathering of the other propeller was obviously deemed high enough to warrant such a safety latch.

Of course, TCMA is intended for ground operation only and has been quoted to be strongly safeguarded against triggering in flight. But still, from my laymans point of view, I was asking myself whether ensuring that TCMA will never kill both engines would be worthwhile, if only as a final barrier in case the system was mistakenly activated inflight.

@Nachtmusak, it is in no way said that Autothrust or any autoflight system is suspected here.

Pulling the power levers to idle or commanding idle thrust in any other way will result in:

1. idling, but still running and responsive engines
2. decaying speed, which will then
3. be noticed by any of the flight crew members and
4. be reacted to by:

a. forcing the thrust levers forward
b. lowering the nose manually, disregarding the flight directors that may still demand a different flight regime.

It will not:
- kill the engines
- kill the hydraulics
- kill the main electric sytems
and trigger an auto-release of the RAT.

Were it different, then the RAT would drop on the 787 in each and every flare whenever the thrust is idled before touchdown.

A question to those familiar with Boeing and the 787: are the thrust levers physically moved by Autothrust or does Boeing use them only to stake an upper thrust limit as Airbus does with active A/T?

There were simultaneous engine failures, but those were due to massive birdstrikes ( US1549 ) or due to epidemic engine failures on Il-62s of various versions (like LOT 007 or LOT 5055 ).

Fuel related total engine failures like Aeroflot 366 or Air Transat 236 at least had the decency to have the engines starve one after another as the fuel in the individual tanks depleted.

But all those are probably highly irrelevant when considering the Air India accident. An engine disintegration or a heavy birdstrike would have been visible on the videos, a sizeable bird would have left some remains. And gradual fuel starvation would have shown some yaw.

As much as I despise the thought, the issue that got AI171 must have come from within the aircraft, although this most decidedly does not infer any wrongdoing by any crewmember.