What happened
On 23 March 2003, a Hughes 369HS, registration G-NIPY, was conducting training maneuvers at Blackpool Airport. The flight involved an instructor pilot and a student pilot performing 'engine-off' landing exercises on a designated hard grass area known as Area 'B'. The weather conditions were favorable, with clear skies and good visibility.
During the session, the instructor performed several demonstrations of autorotation. After observing a tendency for the aircraft to tip forward during run-on landings, the instructor transitioned to zero-speed landings. During one such maneuver, the instructor reduced the throttle to idle to enter autorotation. While the aircraft was flared at the appropriate height, a high rate of descent developed that could not be corrected by the collective lever. As the helicopter made contact with the ground, it began to pitch forward. In an attempt to stabilize the aircraft and prevent further forward movement, the instructor applied significant aft cyclic control. This maneuver caused the main rotor blades to strike the tail boom, resulting in the boom being severed.
The investigation
The investigation examined the aircraft's movements during the final moments of the landing and the condition of the landing site. The crew reported no injuries following the incident. Investigators inspected the area where the touchdown occurred and identified a depression in the ground. The forward 2.5 feet of the helicopter's skids had overhung a hollow in the grass, which was approximately 8 inches deep. This feature was not visible from the air and contributed to the unstable pitch of the aircraft during touchdown.
Findings
- The aircraft's forward skids entered a small, unseen depression in the grass surface.
- This uneven ground caused the Hughes 369HS to tip forward upon touchdown.
- The application of rapid aft cyclic control to counteract the forward pitch caused the main rotor blades to impact and sever the tail boom.