Investigators have disclosed that the altitude selector on the ill-fated Germanwings Airbus A320 was adjusted to extreme values several times, in the captain’s absence, during the previous outbound flight to Barcelona.

French investigation authority BEA revealed the information in a preliminary analysis of the fatal A320 crash in the Alps as the aircraft returned to Dusseldorf on 24 March.

Both flights had been crewed by the same pilots.

On the outbound sector to Barcelona, says BEA, the captain had left the cockpit for about 4min as the aircraft cruised at 37,000ft.

After Bordeaux air traffic control instructed the flight to descend to 35,000ft the altitude selector was adjusted initially to the assigned level, but then briefly changed to a setting of 100ft – the lowest selection permitted on the A320 – and then to 49,000ft, the maximum possible, before being reset to 35,000ft.

Bordeaux controllers told the flight to continue descending to 21,000ft. This level was initially selected but was then changed, again to 100ft, before being adjusted several times.

It was reset to 25,000ft moments before the captain re-entered the cockpit. The aircraft landed in Barcelona about 30min later.

BEA has not given an explanation for the changes in the altitude selection.

But it states that the subsequent crash of the aircraft on the return sector to Dusseldorf occurred while the first officer was again alone in the cockpit and that he “intentionally modified” the autopilot commands to “order the aircraft to descend” until it struck terrain.

“He did not open the cockpit door during the descent despite requests for access made via the [entry] keypad, the cabin interphone and knocks on the door,” says BEA.

The inquiry says that the fatal descent began just over 30min into the return flight.

Marseille air traffic control had given clearance for the aircraft to fly directly to the IRMAR waypoint, and the A320 changed course accordingly. The captain then left the cockpit.

Less than 30s later the selected altitude changed rapidly from the assigned 38,000ft to the minimum setting of 100ft. The autothrust responded with idle power while the autopilot operated in ‘open descent’ mode, in which it prioritises a target speed.

This target speed, normally determined by the flight-management system, was instead manually selected as the A320 descended.

It was initially adjusted to 308kt – higher than the 273kt at which the jet was flying – before being reduced to 288kt. The speed was then changed several times until it reached 323kt.

Inquiries from air traffic control over the aircraft’s cleared altitude were not answered, nor were subsequent attempts at radio contact from civil and military controllers on several frequencies, including the distress channel.

BEA says the buzzer to access the cockpit was activated just over 4min after the captain’s exit, as the aircraft was descending towards 25,000ft. The speed selection increased to 350kt – the maximum setting – and the A320 maintained around 345kt for the remainder of the flight.

Four calls from the cabin interphone were heard as the aircraft descended, says BEA, and “muffled” voices were heard, including a request for the door to be opened.

“Noises similar to violent blows on the cockpit door were recorded on five occasions,” adds the inquiry. The crew of another aircraft also attempted to contact the A320.

None of the calls to the cockpit received a response and the aircraft continued to descend. Ground-proximity warnings started activating some 25s before the impact with terrain. None of the 144 passengers and six crew survived.

Source: Cirium Dashboard