What happened
On 13 March 2014, an Agusta Westland AW1SB helicopter, registration G-LBAL, departed from a private landing site at Gillingham Hall, Norfolk, for a flight to Coventry Airport. The departure took place at night under conditions of dense fog, with visibility reported as being only tens of metres.
The flight crew, consisting of two pilots, was accompanied by two passengers. The commander had planned a vertical departure from the site. After lifting into a hover and moving to the centre of the paddock, the aircraft began a climb. However, at an altitude of approximately 32 feet, the aircraft's pitch attitude transitioned from a slight nose-up position to a progressive nose-down pitch.
As the helicopter gained forward speed and climbed through 120 feet, the crew applied further forward cyclic input. The aircraft's descent rate increased significantly, reaching 2,400 feet per minute, before impacting a line of large hay bales. The impact destroyed the aircraft, and all four fatalities occurred during the accident sequence.
The investigation
The AAIB examined data from the combined cockpit voice and flight data recorder (CVFDR), as well as information from the engine Data Collection Units and the Engine/ cockpit warning systems. The investigation reviewed the flight profile, comparing the accident climb to previous recorded flights.
Investigators analyzed the cockpit audio, which revealed discussions between the pilots regarding the poor visibility and their concerns about lifting out in such conditions. The investigation also looked into the lack of standardized procedures for multi-crew operations and the absence of formal training for the specific departure profile used. Furthermore, the investigation assessed the impact of the lack of external visual cues on the crew's perception of the aircraft's attitude.
Findings
- The helicopter departed a private site at night in dense fog with extremely limited visibility.
- The crew may have been subject to a somatogravic illusion, where the lack of visual cues caused a misperception of the aircraft's pitch due to linear acceleration.
- The flight crew lacked formal training in standardized multi-crew procedures and did not utilize the automatic flight control system effectively.
- The departure procedure used was not a recognized or documented method for achieving the required minimum airspeed (Vmini) during the transition to instrument flight.
- There was an absence of established procedures for two-pilot operations in these specific conditions.
Safety action
Following the investigation, the AAIB issued two Safety Recommendations to the FAA and EASA, requesting amendments to the definition of Vmini to better reflect the practicalities of flight under instrument flight rules when using external visual cues at low speeds.