What happened
On 12 July 2001, a Sikorsky S76A (registration G-BMAL) was performing ground manoeuvres at North Denes Aerodrome, Norfolk. The aircraft was parked into the wind, but positioned with its tail facing the passenger boarding area. To better present the left door for passengers, the commander decided the handling pilot, seated in the left seat, should turn the helicopter 90 degrees to the left.
After completing this taxiing manoeuvre, the handling pilot brought the aircraft to a halt. While attempting to reach across the centre console to engage the 'T' shaped parking brake, the pilot accidentally pulled the commander's collective lever. This caused the helicopter to lift abruptly. The co-pilot reacted by immediately lowering his own collective lever, which resulted in the aircraft landing heavily on its tail.
There were no injuries to the two crew members on board, though the impact caused buckled skin and stringers in the lower portion of the tail cone.
The investigation
Investigators analysed data from the aircraft's Combined Voice and Flight Data Recorder (CVFDR). The flight data confirmed that approximately three seconds before the recording ended, the collective pitch increased, causing the aircraft to pitch nose-up by about 6.5 degrees and reach a maximum altitude of roughly 2.5 feet. The normal acceleration increased significantly, reaching approximately 2g before the recorder's acceleration cut-off switch interrupted power.
The investigation also reviewed company practices. It was noted that the parking brake handle is located on the right side of the centre console, making it difficult to see from the left seat without leaning over. The investigation found that the handling pilot's reach across the console was the primary cause of the unintended collective movement. Furthermore, the company's existing procedures allowed for single-pilot ground manoeuvres from the left seat, and the aircraft checklist lacked specific instructions for ground repositioning.
Findings
- The unintended application of the collective lever while reaching for the parking brake caused the sudden lift.
- The parking brake handle's position required the left-seat pilot to lean across the console, placing the collective lever in the path of his movement.
- The aircraft's checklist did not include a formal procedure for ground repositioning.
- The activation of the CVFDR's acceleration cut-off switch prevented the recording of the peak normal acceleration experienced during the impact.