New Zealand investigators believe the pilot of a Boeing 777-300ER which experienced a runway excursion during touchdown at Auckland did not compensate for the aircraft’s response after belatedly disengaging the autopilot.
The Air New Zealand twinjet – arriving from Melbourne on 27 January 2023 – had been conducting the ILS/DME approach to runway 05R in heavy rain with changes in crosswind direction and strength.
Although the approach was stable, the autopilot was operating in runway-alignment mode, and started applying left aileron and right rudder at 500ft to counter the left crosswind and keep the 777 on track.
The autopilot continued to keep the aircraft on the centreline and maintain its target speed as the wind conditions varied.
While the operator’s procedures recommended disengaging the autopilot at around 300-600ft, to give the pilot sufficient time to establish manual control before commencing the flare, the captain, who was flying, did not disengage until the jet was 67ft above ground.
By this point the aircraft was crossing the threshold of the runway. Just 1s after the autopilot was de-activated the crew started retarding the thrust levers to idle and the flare began 3s after that.
But New Zealand’s Transport Accident Investigation Commission says the autopilot’s runway-alignment mode would have automatically moved the flight controls back to a neutral position after the autopilot was disengaged.
“To continue the correct flightpath established by the autopilot a pilot has to hold the flying controls in the same position that the autopilot had maintained,” it states.
When the controls returned to neutral, it adds, flight-data recorder information shows the pilot “did not hold the control inputs that had been applied by the autopilot” – including left aileron.
As a result, the 777 rolled 3.69° to the right and started drifting right of the centreline.
Although the wind was not strong or gusting, it was reducing in speed and backing more to the left. The pilot was “unable” to counter the combination of the roll and change in crosswind, says the inquiry.
When it touched down – just 9s after the autopilot was disengaged – it veered off the runway onto a sealed shoulder, striking six runway edge lights before returning to the centre.
The inquiry says this excursion was “virtually certain”, given the combination of actions, regardless of the runway condition. While the runway was wet, there was no standing water.
None of the 271 passengers and 16 crew members was injured. But the 777 sustained damage to five of its six right main-gear tyres – one of which, the rear inboard, had deflated – as well as damage to its right brake assembly and wiring harness.
