Investigators have determined that both pilots of an EasyJet Airbus A319 mistakenly selected the wrong intersection during take-off performance calculations at Nice, resulting in less runway distance being available than the crew had expected.

The crew believed they had calculated take-off performance for runway 04R based on a departure from intersection B3 – the most limiting case.

But the UK Air Accidents Investigation Branch found that the crew had inadvertently selected intersection Q3, virtually the whole runway length, for the calculation.

The aircraft was ultimately cleared to depart from intersection A3, which should have offered an additional 316m margin of runway compared with a B3 departure.

But the Q3 miscalculation actually meant the A3 departure reduced the take-off distance margin by 385m – and would have reduced it by over 700m if the B3 intersection had been used.

“At lift-off the [captain] noted that the departure end of the runway was closer than he would have expected but did not perceive any other performance issues,” says the inquiry into the incident, on 29 August last year.

It states that reduced thrust had been used for the take-off roll and that, as the situation emerged, the captain did not feel there was a need to increase power.

Take-off data

Source: Air Accidents Investigation Branch

Indicative performance for Nice 04R departures from B3 (left) and Q3 (right)

Crucially, the investigation found, both pilots made the same mis-selection of the Q3 rather than the B3 intersection. As a result, it says, the take-off performance cross-check was “invalidated” and the error was undetected.

“The flight crew considered that the software user-interface and data presentation was a factor in the intersection selection error being made and subsequently missed,” it adds.

Data entry on the electronic flightbag application was “clumsy and often requires re-entering”, according to pilot testimony to the inquiry. For Nice, it says, the B3 and Q3 intersections are easy to mis-select as they are adjacent.

The captain involved has since reinforced departure error management briefings to include a review of intersection and performance implications.

EasyJet has been working on updating performance software, the inquiry notes, to put greater emphasis on graphic rather than text representation of runway data.

Airbus had also been developing enhanced take-off monitoring for A320s and A330s, using a version of take-off surveillance introduced on the A350 the previous year.

This function, known as TOS2, checks to confirm the aircraft is travelling on the intended runway and that the performance calculations are compatible with available distance. The aircraft (G-EZBI) involved in the incident, however, was not TOS2-capable.