DHL A300-600 rejects takeoff above V1 due to difficulties becoming airborne

[Poiu]

it must also have been aborted after V1 (as VR is at least equal to V1, can’t be earlier). Which doesn’t mean its impossible for the aircraft to stop before the end of the runway.

Unless there was a calculation error and the real V1should have been significantly higher than the one used as in this example:
http://avherald.com/h?article=49d159fc

[Bracebrace]

I would like to avoid any "cause" pinpointing, that's not what I'm here for but related to the comments...

Why should the V1 have to be higher?

From a regulatory point of view, whatever V1 you have chosen within certain acceptable limits (related to brake energy and controllability in the engine out case), the calculation assures that a stop can be made safely when the reject is initiated at V1. In a balanced takeoff, the V1 is chosen based on the assumption that the "go" distance equals the "stop" distance.

If the crew elects to reject beyond V1, there simply is no guarantee by the calculation it can be done. So you only stop if you are absolutely certain that trying to fly will kill you.

Things get even trickier when you use unbalanced takeoff performance. Take any twin jet and calculate a balanced takeoff on a long runway. It might very well be able to stop at V1+5 kts on long runways. Take that completely identical case and use improved climb (unbalanced) performance, chances it will be able to stop beyond V1 are probably minimal...

Concerning gross weight errors: at a speed of 150kts, the tail will move down, there is airflow and the tailplane creates a downforce to create a rotation around the cg. Loading sequence and cg errors however, would create problems like early or no rotation.

So GW errors usually end up in tailstrikes because pilots expect it to fly but it won't. CG errors end up in no rotation (as early rotations are discovered and stopped easily by pilots during the takeoff roll, but the aircraft will fly).

[Poiu]

I would like to avoid any "cause" pinpointing, that's not what I'm here for but related to the comments...

Why should the V1 have to be higher?

I was only hinting at the possibility of a calculation error, where the use of a too low weight led to a too low V1and Vr, as in the case of the CargoB tailstrike in 2008. (https://mobilit.belgium.be/sites/defaul ... INALv2.pdf)

[Bracebrace]

Well, as mentioned, that is less likely as the result of that would not "show" itself as an inability to raise the nose on takeoff, but as wheels staying on the ground beyond 10° of rotation... which ends up in tailstrikes.

An inability to raise the nose for cargo pilots immediatly triggers a loading sequence error in your head. The weight is sequenced more aft during loading (aft cg saves fuel), however if the loading sequence is reversed, the cg is way too much up front and you won't be able to raise the nose at Vr. As a cargo pilot you're usually ready to trim aft if you notice the nose won't raise. But such flights don't make "the headlines".

Pilots are not responsible for loading sequence. There are "tricks" to have a rough idea of what's happening in the back during loading, but they are not bullet proof and sometimes depend on personal experience.

But as said, there are many possibilities that caused this. Gross weight error could be, but I consider it extremely remote. CG or loading sequence is something completely different.

[Poiu]

Well, as mentioned, that is less likely as the result of that would not "show" itself as an inability to raise the nose on takeoff, but as wheels staying on the ground beyond 10° of rotation... which ends up in tailstrikes.

That is exactly how the airline reported the incident, but instead of continuing to raise the nose, which would have resulted in a tail strike, the crew aborted the takeoff:
“The airline reported the crew encountered difficulties to takeoff prompting them to reject takeoff during rotation when the nose gear had already become airborne”

[Bracebrace]

Check, thanks!

[sn26567]

The Aviation Herald today added a paragraph to its report of the incident:

On Jan 28th 2021 Germany's BFU reported in their November bulletin that the aircraft was accelerating for takeoff when the crew felt vibrations just prior to V1. The aircraft increased pitch upon rotation, but did not lift off prompting the captain to reject takeoff. The aircraft came to a standstill on the runway, as result of the heat developed by the brakes all main tyres deflated. The BFU assists the investigations in accordance with ICAO Annex 13 representing the state of registry.

[sdbelgium]

Turns out the trim was set to 1.1 units down by maintenance and it wasn't picked up by the crew (they are used to see 1.0 unit pitch up as the standard setting).

http://avherald.com/h?article=4dfbfe95&opt=0

On Jan 29th 2021 The Aviation Herald received information, that SOP at the operator require to turn the trim to +1.0 trim units (1 unit nose up) after landing. In the morning before the incident flight maintenance worked on the aircraft and rolled the trim to -1.1 units (1.1 units nose down). The load sheet computed a trim setting of +1.1 units for departure. While the load sheet used the +/- notation, the trim itself only shows UP and DN, both +1.1 and -1.1 units are within the green band of the trim settings for takeoff, the crew thus missed that the trim was at -1.1 units instead of the required +1.1 units and experienced a very high pitch force during takeoff rotation. The pitch trim is only checked once during working the pre-departure and takeoff checklists.


On the left the accident trim setting of -1.1 units, on the right the normal trim settings of +1.1 units.