What happened
On 19 April 2008, a Robinson R44 Raven II helicopter, registration ZS-RYR, was conducting a commercial scenic flight in the Drakensberg region of KwaZulu-Natal. After an initial flight from Dragon Peaks Park, the aircraft landed at Crystal Beds to pick up a third passenger from another helicopter.
During the subsequent takeoff attempt, the aircraft encountered a low rotor RPM warning. In an effort to recover the rotor speed, the pilot lowered the collective, which caused the helicopter to descend. As the aircraft moved forward over sloping terrain, it transitioned out of ground effect. The pilot attempted to arrest the descent by applying power, but this further depleted the rotor RPM. The helicopter ultimately struck the ground with significant force, causing the tail boom to separate from the fuselage. There were no injuries among the four people on board.
The investigation
SACAA AIID investigators examined the aircraft's performance capabilities relative to the environmental conditions at the time of the accident. The investigation established that while the helicopter was within its maximum takeoff weight for in-ground-effect (IGE) operations, the conditions at the takeoff site were challenging.
The density altitude at the time was calculated to be approximately 8,900 feet due to the temperature of 17°C. Investigators analyzed the weight and balance, noting that the aircraft's takeoff weight of 2,426 lbs exceeded the calculated out-of-ground-effect (OGE) limit of 2,300 lbs by 126 lbs.
Findings
- The pilot over-pitched the rotor system during the takeoff phase.
- The aircraft's gross weight exceeded the maximum allowable limit for out-of-ground-effect performance by 126 lbs.
- The pilot's attempt to regain rotor RPM by lowering the collective, followed by an attempt to arrest the descent with power, led to a further decay in rotor RPM.
- The transition from in-ground-effect to out-of-ground-effect over sloping terrain contributed to the loss of lift and subsequent impact.