The Australian Bureau of Air Safety Investigation (BASI) is treating as "very serious" an incident in which a Kendell Airlines Saab 340 carrying 30 passengers stalled and rolled almost inverted in light icing conditions on 11 November, injuring a flight attendant.
The Kendell flight was in a holding pattern, maintaining 15,000ft (4,500m) and 154kt (285km/h) indicated airspeed at night and in turbulence. The speed slowly bled back to 133kt during a 28° banked turn. The autopilot became disconnected, and the aircraft rolled through 126°, pitching 36° nosedown, losing in the process about 2,500 ft in altitude before the stall was recovered.
Although aware of icing conditions, the crew had apparently assessed that the degree of wing icing did not warrant de-icing boot activation, and they had received no warning of approaching stall, apart from momentary buffet a second before the autopilot disconnected, at which point the stick shaker may also have activated momentarily. Clean stall speed in the configuration is about 109kt.
The BASI investigation will include a review of the type's icing certification, and of the performance of the stall warning and protection systems.
Saab says that the 340's ice protection systems and operation in icing conditions were fully reviewed by the FAA following an ATR 72 crash in October 1994 at Roselawn. Saab says: "We did not think that was necessary, but the aircraft came through those trials with flying colours."
Meanwhile, the US National Transportation Safety Board has made extensive recommendations to the US Federal Aviation Administration about operating turboprop aircraft in icing, following its investigation of the January 1997 Comair Embraer Brasilia crash near Detroit, in which 29 people died.
Source: Flight International
