An incident involving a Swiftair aircraft carrying 22 passengers which stalled in icy conditions was caused by pilot error, investigators in Spain have concluded.
The investigation determined that the pilots reacted incorrectly to events and weather conditions and also exhibited “inappropriate” use of automation.
The turboprop (EC-KKQ) lost airspeed and height and rolled to excessive bank angles during the Alicante-Madrid service on 9 September 2017, and the captain’s response suggests he initially did not recognise that the aircraft was stalling.
Eight minutes before the stall the aircraft had entered icing conditions which then worsened into severe icing.
Investigation authority CIAIAC says the pilots received a degraded-performance warning but did not carry out the associated checklist.
They “did not consider” the ATR’s behaviour as they fixated on its climb, says the inquiry, forcing the aircraft to its limits and then attempting to climb “beyond” these limits.
Their focus on climbing resulted in their selecting autopilot modes which were prohibited in icing conditions, including vertical-speed mode, leading to a severe degradation in performance and the stall just above 17,000ft.
The ATR lost more than 1,660ft in altitude in 33s and experienced a series of uncommanded pitch attitudes – from 6° nose-up to 11° nose-down – and bank angles, rolling from 58° left to 11° right and then back to 41° left. It also reached a maximum angle of attack of 19.6°.
CIAIAC says weather information had been provided to the crew anticipating that much of the flight would take place in icing conditions, with moderate icing at 14,000-15,000ft over the waypoint NARGO.
“The reality of what happened in the flight showed that, in effect, icing occurred near that point, only it was worse than forecast,” the inquiry states.