AAIB investigation to Saab-Scania SF340B, G-LGNM
Stall warning in icing and mountain wave conditions, en-route from Aberdeen to Sumburgh, 3 October 2014.
The aircraft’s rate of climb deteriorated in icing conditions, while the aircraft was experiencing mountain wave effect during the latter part of a climb to FL130. Once level, the aircraft did not accelerate as expected and a descent was initiated, with the autopilot engaged using vertical speed mode. An unusual vibration was then experienced, followed by a stall warning system activation and the autopilot disengagement. The aircraft was recovered in a non-standard manner, a safe airspeed was achieved and the autopilot was re-engaged. Subsequently, a normal landing was made at the planned destination.
Unusual ice formation, seen on the wings, corroborated calculations by the manufacturer that the aircraft had encountered severe icing.
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Published: 10 September 2015
Date of occurrence: 3 October 2014