The Air France aircraft, en route to Los Angeles on 30 September 2017, suffered the failure of its outboard right-hand Engine Alliance GP7200 powerplant as the jet was climbing from 37,000ft to 38,000ft.

Air France procedures for engine failure in cruise require the crew to set power at maximum continuous thrust and to determine the maximum engine-out altitude, which is calculated by the flight-management system.

This maximum engine-out altitude enables the aircraft, at maximum continuous thrust, to maintain level flight at the long-range cruise speed – the Mach number at which the specific flight range is 99% of the maximum flight range. //

Airbus calculated that the long-range cruise speed of the aircraft, at the time of the failure, was just under 289kt – which would have given a maximum altitude of 34,000ft.

But French investigation authority BEA states that the calculation of engine-out altitude assumes the failed engine is windmilling and does not take into account possible deterioration of aerodynamic performance, notably the additional drag resulting from seized rotors or other uncontained failure damage.

The A380’s entire fan hub disintegrated during the incident, shearing off the engine inlet.