David Learmount/BARCELONA

Investigators are considering pilot spatial disorientation as a possible cause of the 10 January Crossair Saab 340 accident at Zürich, Switzerland, after running a simulation.

According to the flight data recorder - downloaded by the Transportation Safety Board of Canada - the pilot rolled the aircraft nearly inverted, but then appeared to recover attitude awareness and reduced the extreme bank by 70° just before the aircraft hit the ground.

Preliminary statements issued by the Swiss investigators indicate that the captain had begun a left turn as he was cleared to do his climbing departure from Zürich, but when the flight management system locked on to the Zürich East VOR beacon and "recognised" a right turn as the more direct route, the flight director led the pilot to turn right (Flight International, 4-10 April).

The fear is that the pilot may have followed the flight director right while still thinking of a left turn, which would have caused conflicting sensory inputs. The simulation shows that the extreme right bank was applied manually in short bursts, recognised as a sign of confusion, but there was never any significant pitch input and the aircraft spiralled into the ground with about 1g positive acceleration throughout the fatal descent.

Crossair flight safety and security officer Matthias Schmid says no definite conclusions can be drawn, but adds that the conditions were classic for disorientation. Apart from conflicting turn inputs, it was night, and the landing lights were probably on while the aircraft was in cloud with slight rain.

Source: Flight International