Investigators believe a software anomaly in an EasyJet Airbus A319’s electronic flightbag might have resulted in its crew’s using take-off performance data for the wrong runway at Belfast.
The crew had opted to depart from intersection B to runway 25 for a service to London Luton on 25 June last year.
As a precaution the captain had used the electronic flightbag to calculate take-off data for a wet runway.
When the pilots reviewed the data, they changed the runway condition to ‘dry’, to see whether this would enable a lower-thrust take-off.
Although the new calculation did provide for a reduced thrust setting, the crew had not cross-checked the data on which the calculation was based. The new take-off data assumed that the much longer runway 07 was being used.
Analysis by the UK Air Accidents Investigation Branch found that the runway selection could unintentionally be changed while amending one variable – in this case, the runway condition – using the flightbag touchscreen.
The inquiry could not determine the specific circumstances of the change. But it states: “The risk associated with using touchscreen input devices, which are on all the time, is that any inadvertent touch of the screen by a conductive source may change a field on the screen.”
Although the aircraft’s take-off acceleration was only marginally slower, its calculated rotation speed was 135kt – some 10kt higher than it ought to have been.
At 115kt the captain noticed the end of the runway approaching and realised that the aircraft would not have sufficient room to stop if the take-off was aborted at the V1 decision speed.
The side-stick was pulled back for rotation around 7s later than it had been for previous similar runway 25 intersection departures, and the A319 became airborne some 200m before the end of the runway.
Airbus estimated that using runway 07 data for the departure could have resulted in an overrun at 75kt if the take-off had been aborted at a V1 of 136kt.
The flight proceeded without further incident. None of those on board the aircraft (G-EZAA) was injured.
Neither the carrier nor the manufacturer had been aware of the anomaly in the Airbus FlySmart software. The inquiry says the electronic flightbag was “not optimised” for touchscreen, but an updated version of the software will correct the flaw.
EasyJet stresses that it co-operated fully with the investigators during the inquiry.
"As soon as we were informed by the operating pilot, EasyJet immediately launched a safety investigation to understand what happened and ensure that the airline could learn any lessons from the incident," the airline says.
“EasyJet’s specialist team conducted a thorough safety investigation, in consultation with the AAIB, and as a result it made a recommendation to its internal procedures. The safety of its passengers and crew is always EasyJet’s highest priority."