What happened
On 26 September 2009, a private Robinson R44 Raven II, registration ZS-RWD, departed from a private helipad in the Muldersdrift area of Gauteng for a visual flight rules (VFR) mission. The flight, which included a pilot and one passenger, initially proceeded normally, with the pilot establishing a stable hover at approximately 6 to 8 feet above the ground.
As the aircraft transitioned into forward flight at an altitude of roughly 20 feet and a speed of 25 knots, the engine and rotor RPM began to decay. In an attempt to manage the situation, the pilot increased the throttle and lowered the collective pitch as much as the low altitude permitted. Despite these efforts, the RPM continued to drop, forcing the pilot to execute an emergency forced landing. The resulting hard landing caused the main rotor blades to strike the tail boom, severing it from the fuselage, and subsequently caused the helicopter to roll onto its left side. Both occupants escaped the zero injuries.
The investigation
SACAA AIID investigators examined the wreckage and the mechanical components of the aircraft. A bench test of the Textron Lycoming engine revealed no operational abnormalities or pre-existing failures. The investigation also reviewed the aircraft's weight and balance, finding that the helicopter was operating outside its prescribed center of gravity envelope, specifically slightly forward of the allowable limit. Furthermore, investigators analyzed the environmental conditions, noting that the combination of the airfield's elevation and the ambient temperature resulted in a high density altitude of approximately 6,100 feet.
Findings
- The primary cause of the accident was over-pitching during take-off, which led to the hard landing and subsequent rollover.
- The pilot utilized an incorrect take-off technique during the transition phase.
- High density altitude conditions significantly impaired the aircraft's performance.
- The aircraft was operating with a center of gravity outside of the manufacturer's recommended limits.
- The pilot's previous flight experience was primarily at sea level, which may have contributed to a lack of familiarity with high-altitude performance challenges.