What happened
On 28 July 2008, a Hughes 269A helicopter, registration G-SHPP, was conducting a private reconnaissance flight near Peacehaven, East Sussex. The pilot intended to survey a potential landing site before returning to Redhill Airfield. After performing two orbits of the area, the pilot decided to approach the field from the northwest, entering into a hover at approximately 1-00 feet above ground level.
To avoid flying near a group of horses, the pilot performed a pedal turn to depart on the same ground track used during arrival. Because this departure was downwind, the pilot attempted a gradual transition from a hover to forward flight. During this maneuver, the aircraft began to sink. In an attempt to correct the descent, the pilot raised the collective lever, which triggered an overpitching of the main rotor.
As the aircraft continued its descent, the pilot observed a drop in rotor RPM. In an effort to restore the RPM, the pilot lowered the collective, but the aircraft was at too low an altitude to recover. The reduction in rotor speed resulted in a loss of tail rotor authority, causing the helicopter to yaw to the right. The pilot's attempts to correct the yaw with left pedal were unsuccessful. The aircraft eventually struck a fence at the top of a small slope, causing it to roll over to the left. There were no injuries to the two occupants, though the aircraft was damaged beyond economic repair.
The investigation
The investigation focused on the mechanics of the rotor overpitching and the environmental factors present during the flight. Investigators examined the engine performance and the aerodynamic consequences of the pilot's control inputs during the downwind transition.
Findings
- The primary cause of the loss of control was rotor overpitching, which led to a decrease in rotor RPM and a subsequent loss of tail rotor effectiveness.
- High ambient temperatures at the time of the accident likely reduced the available engine power.
- The aircraft was operating near its maximum gross weight.
- The power requirements for a downwind transition were higher than those needed for an into-wind departure.
- On the Hughes 269A, using left pedal input increases the power demand on the engine due to the anti-clockwise rotation of the main rotor.