Somatogravic illusion affected Air Arabia Maroc captain before A320 nearly hit sea

Crew under time pressure took off from Catania without V-speeds in flight-management system.
Investigators believe the captain of an Air Arabia Maroc Airbus A320 experienced somatogravic illusion during a night take-off from Catania, after which the aircraft descended and came close to striking the surface of the sea.

Italian investigation authority ANSV states that the crew had been under time pressure for the ferry flight to Amman on 20 September last year.

There was a need to revise the flightplan to avoid Israeli airspace and change the alternate airport – which took 35-40min – and depart before Catania airport closed for the night.

The A320 took off from runway 08 without the V-speeds having been entered into the flight-management computer.

ANSV states that the crew testified to having calculated the V-speeds correctly on the electronic flightbag, with the first officer entering them and the captain checking.

But as the aircraft rolled along the runway the crew realised, at about 60kt, that the speed reference system and autothrust indications were not available.

“This situation would be not compatible with correct insertion of the take-off speeds,” says the inquiry.

Although the aircraft was well below the V1 decision speed of 131kt, the captain opted not to abort the take-off, given the airport’s closure and a perception that managing the take-off would not be difficult.

The combination of a lightly-loaded aircraft and use of take-off/go-around mode, rather than ‘flex’ mode, resulted in high acceleration.

ANSV believes this acceleration, combined with the darkness and the absence of visual references over the Mediterranean Sea, enabled somatogravic illusion to take hold.

This illusion results in perception that the aircraft’s nose-up pitch is too steep, leading pilots to react with nose-down input.

The aircraft had already lifted off with a shallow pitch – initially just 7°, rather than the typical 15° – and over 12s it climbed to just 309ft before the captain commanded nose-down input with the sidestick.

“Although during the interview the captain did not report he felt spatially disoriented, the situation was highly prone to induce spatial disorientation,” says the inquiry.

“The captain remembered [starting to give] pitch-up inputs, while the recorded data show the opposite.”

Flight-data recorder information shows the jet reached a maximum height of 383ft.

At the point when the autopilot was engaged, the aircraft was already descending. The crew training manual states that the aircraft should be flown on the intended path before activating the autopilot.

“These recommendations were not followed,” says the inquiry and, as a result, the autopilot synchronised with a vertical descent rate of 1,900ft/min rather than a climb.

Terrain warnings and ‘pull up’ alerts were issued before the captain began arresting the descent. The aircraft descended to 41ft above water before recovering and climbing.

It continued to Amman without further incident and none of the six crew members, the only occupants, was injured.

ANSV says flight-data recorder information and the aircraft’s behaviour were “coherent” with the V-speeds not having been inserted into the flight-management system before take-off.

While the possibility of a system malfunction was considered, there was no evidence of such. The inquiry also queried whether the crew, given the time constraint, simply omitted this step.

ANSV points out that the original flightplan, and the revised version, were both based on a departure from Catania’s runway 26, rather than runway 08.

Simulation work indicated that, if the runway changed after the insertion of the V-speeds, then the speeds would be deleted and the flight-management system would require reconfirmation.

The A320 involved (CN-NML) was fitted with a Thales flight-management system that had an older software version installed, which was not capable of providing a warning about the missing V-speeds – unlike a more recent update.

ANSV points out that – aside from the captain’s failure to establish the proper attitude and climb profile – the first officer’s actions suggest a “lack of assertiveness”, given the decision not to intervene and abort the take-off.

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