What happened
On September 10, 1978, a Rockwell Commander 114, registration HB-NCM, was conducting a visual flight rules (VFR) flight from Exeter to Leicester. The flight was operated by a Swiss crew and passengers. Before departure, the pilot was informed by a meteorologist at Exeter that low clouds were present in the Bristol/Gloucester area and that VFR conditions would be difficult. The crew decided to attempt a low-level route, intending to follow the River Severn to avoid higher terrain.
As the aircraft approached the Bristol area, it encountered deteriorating weather. While attempting to navigate through a valley to bypass hills, the aircraft entered low clouds with poor visibility. While flying in the clouds and executing a left turn, the aircraft entered a steep descent. The aircraft struck the edge of a clay pit at a high rate of descent, overturned, and collided with a pile of wood before catching fire in a nearby stream bed. All four occupants were killed instantly.
The investigation
The investigation established that the aircraft was airworthy, correctly loaded, and free of mechanical defects at the time of the accident. Investigators determined that the pilot, who was not qualified or trained for instrument flight rules (IFR), attempted to maintain visual contact with the ground by flying at low altitudes through hilly terrain despite the presence of low clouds and fog.
Analysis of the flight path suggests the aircraft was likely flying at an altitude of no more than 800 feet when it entered the clouds. The investigation calculated a significant sink rate of approximately 1,500 to 1,600 feet per minute during the final moments. The presence of moderate to strong turbulence in the area likely further complicated the pilot's ability to maintain control during the turn.
Findings
- The pilot continued low-level navigation over hilly terrain after encountering deteriorating weather conditions.
- The crew did not request a detailed route weather forecast prior to departure.
- The pilot was not rated or trained for instrument flight, making the necessary maneuvering in clouds impossible to perform safely.
- Low clouds, poor visibility, and heavy turbulence made safe visual navigation through the terrain impossible.
- The aircraft entered a steep descent while attempting a left-hand turn within the cloud layer.