Incident Details
On 20 January 2020 at 2039 local time, a De Havilland Aircraft of Canada Ltd. DHC-8-311, registration LN-WFO, operated by Widerøes Flyveselskap AS as flight WF577, experienced a serious incident in the airspace approximately 20 nautical miles north of Bergen Airport Flesland. The aircraft was en route from Kristiansund Airport Kvernberget (ENKB) with 2 pilots, 1 cabin crew, and 14 passengers on board. No injuries were reported.
Sequence of Events
During climbout from Kristiansund, the aircraft inadvertently flew into an area of severe icing conditions. The crew took corrective action by changing course and altitude but could not sufficiently limit the duration of exposure to severe icing. Ice formed on the aircraft and inside the engine air inlets.
On approach to Bergen, the left engine lost power, followed by the right engine, and then the left engine again. The aircraft's automatic ignition system restarted both engines, but the start-up sequence took time, leaving the aircraft without engine power for a brief period. The engines flamed out due to ice detaching from the engine air inlets. The ice either entered the combustion chamber as slush and water, causing a flameout, or disrupted the airflow into the engine sufficiently to stall it. The crew acted professionally and landed the aircraft safely at Flesland.
Investigation and Findings
The Norwegian Safety Investigation Authority (NSIA) conducted a full investigation. They identified shortcomings in Widerøe's documentation concerning operations in icing conditions. The NSIA also called for the aircraft manufacturer De Havilland to issue a warning that the aircraft's engines could stop if exposed to severe icing conditions. Additionally, the use of weather radar by air traffic services was noted as a topic requiring reassessment.
The investigation highlighted that neither moderate nor severe icing is explicitly defined in joint European regulations. The NSIA requested clear definitions for use by pilots and meteorological personnel.
Safety Recommendations
The NSIA submitted three safety recommendations following this investigation. One was addressed to Transport Canada, one to the Norwegian Civil Aviation Authority, and one to EASA. These recommendations aim to improve safety and prevent similar incidents in the future.