AAIU report into in flight emergency on Dc8 N865F

The Air Accident Investigation Unit of the Department of Transport today issued it's final report into an in flight emergency which occurred to Murray Air Dc8 N865F at Shannon on March 28 2008. The aircraft had departed Shannon's R24 at 22.18 for a sector to Qatar with a cargo of baggage and personal belongings. Shortly after departure and while still in the initial climb out phase the aircraft suffered a compressor stall to the nr. 1 engine. This engine was shut down following which a stall occurred on the number two engine. The crew declared an emergency and requested a return to Shannon, just over 4 minutes into the flight. The crew commenced the engine anti ice routine after which the situation stabilised allowing firstly the nr. 1 engine to be relit followed by the nr. 2 engine. 

When the incident occurred the aircraft was 4nm south of the airport over Askeaton Co. Limerick and under the guidance of Approach Control having been handed off by Shannon Tower. The loss of two engines resulted in an increase in the aircraft's VMCA (minimum airspeed to maintain directional control) to 208kts which was higher than the aircraft's actual airspeed. In order to regain control it was necessary for the aircraft to descend to increase air speed. The minimum altitude achieved during the incident was 1,100 ft. The Approach Controller is commended in the report for his quick thinking in vectoring the aircraft for R06 once it became apparent that a left hand downwind for R24 would have been incompatible with the aircraft's flight profile due to high terrain. 

In the event, the aircraft continued on for a right hand downwind to make an overweight landing on R24. No damage was recorded. The subsequent investigation showed that the probable cause of the incident was rapid icing of the engine nacelles on departure which caused a disturbance of the engine inlet airflow thus causing the compressor stalls. The JT3D engines fitted to the Dc8 have an engine de-icing feature which requires engine bleeed air to be pumped around the nacelles. This procedure causes a significant loss of engine power which reduces the aircraft's MTOW due to less climb thrust being available. As a result there may be a reluctance by air crew to utilise the feature unless absolutely necessary. The report does make mention that the Dc8's crew would have been unfamiliar with the local met conditions at Shannon and not predicted the high possibility of engine icing occuring in the ambient temperature of 6C at the time of their departure from the airport.

Posted 090409