German investigators detail brake input before Vietnam Airlines 787 overrun

A Vietnam Airlines Boeing 787-9 sustained a tail strike departing Munich on 15 August. Its take-off roll was disrupted by brake input that investigators have not yet explained.

The German investigation authority BFU said the aircraft was cleared to depart from runway 26L. Flight-recorder data shows take-off mode was selected about 25 seconds after clearance. Almost at once, with the jet still near the start of its run, the recorder captured pedal movement on the left-hand pilot's side, affecting both rudder and brakes.

Braking began as the aircraft passed 80kt, roughly 600 metres into the roll, and stayed active as speed increased. Some 48 seconds after the first pedal movements, airspeed reached 168kt and held there for about 18 seconds, with brief dips and recoveries recorded during that period.

The crew had calculated a V1 of 169kt and a rotation speed of 175kt for the flight to Hanoi. Four pilots were in the cockpit. The assigned commanding pilot sat on one of two jumpseats behind the pilots flying and monitoring.

Braking-system units logged peak application of 27% on the left main gear and 17% on the right. Tyre tracks from the main landing gear were found alongside the B4 taxiway, about 3,000 metres from the threshold of 26L and around 1,000 metres from the runway end.

Rotation started at 163kt, about 12 knots below the required speed, as the aircraft reached the threshold of the opposite runway, 08R. Just before that, the preliminary findings indicate, the right-hand pilot had manually increased power. The 787-9 overran and struck its tail.

BFU has reached no conclusion on why the brake input occurred.