Investigations have traced an EasyJet A319 take-off performance incident at Malaga to a software anomaly in a particular electronic flightbag function.
The flaw enabled the flightbag to display information for two different runways simultaneously, which led the crew to use take-off calculations for runway 13 during a departure from runway 31.
EasyJet subsequently disabled the function – known as ‘multiple runway computation’ – from the flightbags on its fleet a couple of weeks after the 14 April 2016 incident.
This function of the Airbus FlySmart software is designed to calculate take-off performance for several selected runways to provide a comparison to the crew.
But UK Air Accidents Investigation Branch analysis found that the software could display detailed information for one runway while simultaneously showing take-off performance data for another.
“The flight crew did not notice this during cross-checking,” says the inquiry, adding that neither Airbus nor the carrier was aware of the software anomaly at the time.
Investigators state that the flightbag had used an earlier version of FlySmart, and that the later versions are unaffected.
When the pilots undertook critical data entry checks, they did not notice that, while the intended runway 31 had been selected from a menu box at the top-right of the flightbag display, a results section on the same page was still showing data from runway 13.
“As most of the take-off performance calculations were usually performed using the ‘single runway’ option, the crew were familiar with verifying the selected runway in only one place – at the top-right of the screen,” says the inquiry.
“With a particular runway selected at this upper position on the screen, it is possible to make the assumption that the corresponding take-off performance figures on the ‘results’ page are related to that runway.”
The two runways are physically the same length, but runway 31 departures head inland towards rising terrain, while departures from runway 13 head out to sea.
Although the take-off was normal, the captain had noted that calculated speeds and the thrust-reduction altitude were lower. He assumed the carrier had changed some of the aircraft’s performance algorithms but, nevertheless, checked the calculations during the cruise, at which point he noticed the discrepancy in the displayed runway data.