Posts about: "Takeoff Roll" [Posts: 65 Pages: 4]

Looking at the video of the takeoff roll, it seemed normal, normal rotation, normal initial climb. Other incidents with incorrect performance data or incorrect flap setting (especially flapless) resulted in an extended rotation phase, often with a tailstrike which doesn't seem to be the case here. So the flaps were probably set correctly.

This aircraft then climbed okay but then 3 things happened

1. They didn't raise the gear (maybe due distraction)
2. They apparently called a mayday for an engine problem
3. The aircraft started to sink and continued to do so until ground impact

The videos and the flight path don't seem to show lateral deviation or rudder application but if they called mayday for an engine problem we've got to go with that.

Perhaps the flaps were retracted early but I don't see any pitch change, just sink.

As the aircraft is certified to fly on a single engine, it should have done so. That it didn't seems to indicate that the other engine also stopped developing the required thrust.

Whether it was shut down unintentionally or damaged due to some environmental factor remains to be seen but my moneys on inadvertent shutdown.

I think it may be a simple case of inaccurate takeoff performance data, or inadvertent retraction of flaps instead of gear (this can happen and does happen).

I'm no expert and open to discussion, but it looks to me like the slats are somewhat extended but the flaps weren't, or at least not from the angles we have seen so far. The autogap system on the B787 will automatically extend the slats if they are already in the middle position (i.e Flaps 1) with KIAS <225. Perhaps, either the inaccurate input for takeoff performance produced figures that allowed a Flaps 1 departure, leading to a longer takeoff roll and then once out of ground effect, insufficient climb gradient and a pilot induced stall. Alternatively, at the point where you would likely ask for gear up, the PM has inadvertently selected Flaps 1 from Flaps 5 leading to the same effect. Pilots experienced startle and shock, declared a Mayday as they knew they were descending when they shouldn't be and didn't have time to appropriately react.

Dual engine failure is obviously a possibilty however rare it might be. but it doesn't look like any catastrophic failure from the video. Clearly a sad day for all in aviation and looking forward to the official investigation and results, hopefully something we can all learn from.

nothing was normal the plane rotated right at the end of the runway far too late and barely climbed at all for 10 seconds before falling 20 seconds and finally crashing 30 seconds after take off.

The most obvious answer is low power/flaps setting if the engines were weird they would have probably aborted take off. Bird strike/engine issue during take off roll after v1? Super unlikely but never say never

Anyone that has flown the 787 knows that at max ATM and TO2 the takeoff roll is extremely long. With it flying that far and it being rather hot also a chance it wasn't that derated. I have no experience operating in India so I know nothing about that airport, the conditions, if it's a climb limited field, runway limit, clearways etc. But a 787 having a long take off roll is certainly not unusual.
The climb performance one inop on the -8 is also eye openingly average. (Not making any suggestion that was the case here as it clearly looks as if were not.)

My theory on this is a wrong weight/temperature entry, too much derating, attempted take-off in too low an energy state and subsequent departure stall.

From the airport cam video, the aircraft seems to stick off just at the end of the runway.
Both engines are working at full blast until at least obstacle clearance height, they kick up unusual amounts of dust for a take-off.

Theoretical sequence of events:
1. Pilots entered the wrong take off perf data
2. During the take-off roll they realize that the aircraft isn't picking up enough speed but too late to reject and firewall the throttles
3. They use up the whole runway and get the aircraft off the ground in ground effect
4. Ground effect ends and they fail to maintain a positive rate of climb, hence gears stay down
5. Aircraft stalls and sinks into the ground

Textbook departure stall and failure to pitch down to recover from it.

Takeoff roll and rotation looked normal. No tail clearance or any other issues to indicate anything abnormal until after the main gear left the runway and they were not retracted.

I'm sorry but pilots are taught to recognise lack of acceleration during takeoff. They're also taught about cross checking FMC entries during setup. How are they taught? By me and many others.

Even if the pilots had the wrong FMC performance, it would be noticed in the before takeoff cxl.

So why did the RAT deploy?

Something did happen for sure when the aircraft was obscured behind that shed or building during the takeoff roll. It definitely does yaw to the right and has a slight bank and counter correction thereafter. A previous poster also mentioned it. I tried to quote him my browser hung up. The winds weren\x92t that strong at that time for the aircraft to yaw into the wind after rotation.

Is it possible that a reduced power takeoff error is a factor, similar to the EK407 near-accident in Melbourne? It might be the camera angle in the video that shows the takeoff roll, but it did not look like the aircraft was accelerating normally?

The comments that you are criticising are based on a subsequent release of ADS-B data from FR24 containing 113 unique messages.

While those still have the 4\xbd minute gap while the aircraft was presumably backtracking, they resume during the latter part of the takeoff roll where reception is clearly better.

There is little doubt that when they abruptly cease after the aircraft is airborne it's because the plane has stopped transmitting.

No, you can't generalise from that.

For everyday flights, FR24 displays enough plot points to produce a reasonably smooth track, with plots typically at 6-8 second intervals, while suppressing intermediate points to save bandwidth. That's why the initial download for the accident flight only had 4 plot points.

The supplementary "granular" data (FR24's description) contains plots towards the end of the takeoff roll at roughly 0.5 second intervals. So we can reasonably conclude that the aircraft's transponder stopped squittering within a second (probably less) of the final plot point.

TCMA independently monitors each engine and automatically reduces engine power when it detects the failure of an aircraft engine to throttle down when idle or low thrust is selected. TCMA will only cut fuel to an engine if the aircraft is on the ground and it detects an anomaly between the high power condition of the aircraft's engine when the thrust levers are set for idle or low thrust. There is no evidence in the video of the takeoff roll for AI171 to indicate that its thrust levers were set at idle or low thrust.

It was assumed for decades that in the event of uncontrollable high thrust (UHT) that the pilot would cut the fuel. Until there was a UHT event (1999?) on the takeoff roll and the crew - in an RTO - rode it all the way down and off the runway without cutting fuel. TCMA is primarily about the RTO scenario (throttle back to idle), and after that fleet event it became a requirement for FAA Part 25 certification.

What Alty posted is correct. There have always been single faults in the engine control systems that could cause uncommanded high thrust (UHT) - and such failures were considered in the safety analysis (e.g. FMEA) with the note that it wasn't unsafe as the pilot would shutdown the affected engine. Then there was a 737-200 event (JT8D engines) (1999 sounds about right - I'm thinking it was either an Egyptian operator or it happened in Egypt, but don't hold me to that) - the JT8D had an issue with excessive wear of the splined shaft that provided the N2 input into the hydromechanical fuel control. In this event, that splined shaft started slipping - causing the fuel control to think the N2 was below idle, and it keep adding fuel to try to get the N2 back above idle. This caused the engine to accelerate uncontrollably - the pilots pulled back the throttle and performed an RTO, but the engine didn't respond, and they went off the runway at low speed. Everyone evacuated safely, but the aircraft was destroyed by fire.

The FAA pointed to this accident and said we couldn't depend on crew action to shutdown a runway engine, and therefore any single failure that could result in uncontrollable high thrust was not compliant with 25.901(c) (basically says no single fault can result in an unsafe condition). This basically made every commercial airliner flying non-compliant as every turbine engine control system at that time had single faults that could cause UHT . A consequence of this was everyone was effectively prevented from certifying any further engine control changes since we couldn't show compliance with 25.901(c) (even if the change actually improved safety). The FAA and EASA were forced to issue partial exemptions for all existing aircraft/engine combinations, with the stipulation that they wouldn't certify any new engines that didn't address UHT. A working group was put together at Boeing to come up with some way to comply - and they eventually came up with TCMA , only active on the ground since UHT was only considered unsafe when on the ground - first incorporated on the GE90-115B/777-300ER/200LR.

I've never been 100% comfortable with TCMA (for reasons that should be all to obvious right now), but the regulators gave us few options.
BTW, during the early development of the 747-8, we didn't have a robust way of providing air/ground to the FADECs - which the FAA immediately found objectionable since they never wanted the risk of TCMA being active in-flight. I eventually came up with a design change that would provide a robust air/ground indication (it solved several issues we were confronting at the time), so that concern went away - which made the FAA very happy.

Based on the video taken from the left of the flight path, can we determine at what point of the runway rotation occurred? Is there positive confirmation that the takeoff roll started at the beginning of the runway ? Are the two indicative of trouble before rotation, as the Times states ?
Source: https://www.thetimes.com/world/asia/...rash-vhqw6b7v3 (paywalled)

In the very early posts it was concluded from the evidence available that the takeoff roll started at the begining of the runway and the rotation was with around 4000 ft of runway remaining. The rotation point was assessed to be similar to other take offs. Aircraft attitude and flight path during rotation and lift off was assessed to seem normal.

Yes.
1250m from the end of the runway, between high speed C and D, adjacent to the closed high speed.
There is nothing unusual with the rate of acceleration that is observable ninth video. You can work that out using google earth and the Indian AIP and/or state airport charts. The weight of the plane can be estimated by the flight time and pax load and an allowance for cargo. The simplified TO performance is in the inflight performance section of the FCOM, which you may find a copy on line.
The aircrafts rotation has no obvious issues, until a few seconds after achieving an attitude that is consistent with the V2+15-25 range, at which point the ROC visibly starts to decay.

IMO, I don't know if that is trustworthy - the FR24 ADSB data seems to show that the aircraft was at 21ft AGL between the 1500ft and 2000ft markers from the end of the runway.

https://www.flightradar24.com/blog/f...rom-ahmedabad/

I don't know if I'm allowed to post pictures - my last post with a picture didn't show up, so I'll try adding it separately from this one. It's basically an overlay of the FR24 blogpost map on a google maps satellite view of VAAH.

Yes. Thank you tdracer. All those postulating TCMA / FADEC faults please read and understand this clear explanation.

Then, ask yourselves which extraordinarily low probability bundle of previously unrevealed faults could spontaneously manifest themselves on both engines simultaneously.

Also ask yourselves why these faults manifested at that critical phase of flight and not during taxiing or take-off roll when some of the TCMA sensors would have been primed.