What happened
On 10 March 2006, a Robinson R44 Raven II helicopter, registration ZS-RAT, was conducting a private flight from Rand Aerodrome. The mission involved a stop at the Kloof Hospital helipad in Pretoria to collect a second passenger for a journey to Marken, Limpopo Province. After the additional passenger boarded, the pilot successfully established an in-ground effect hover on the hospital's rooftop helipad and began the transition to forward flight.
As the aircraft moved away from the roof structure, it transitioned from in-ground effect to out-of-ground effect flight. During this transition, the helicopter lost altitude, and the pilot received low main rotor RPM warnings. In an attempt to maintain flight, the pilot lowered the collective and overrode the governor to increase power; however, this action failed to stabilize the aircraft. The helicopter descended and struck trees approximately 100m from the helipad in a nose-down attitude. The impact resulted in serious injuries to one passenger and minor injuries to the pilot and the second passenger. The aircraft sustained substantial damage, including the destruction of the cabin and instrumentation.
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 the density altitude was approximately 7,500 feet due to a temperature of 26°C. While the helicopter's takeoff weight of 2,437 lbs was within its maximum certified limit, it exceeded the calculated maximum allowable weight for out-of-ground-effect flight, which was 2,380 lbs.
Findings
- The pilot failed to perform a new weight and balance calculation after picking up the second passenger.
- The pilot did not consult the Pilot's Operating Handbook (POH) hover charts to verify performance limits for the high density altitude.
- The pilot over-pitched the helicopter during takeoff, leading to a decay in main rotor RPM that could not be recovered.
- The transition from the rooftop's ground effect to out-of-ground effect flight placed the aircraft in a state where the power required exceeded the power available.
- The pilot did not follow the required regulatory procedures for conducting a non-scheduled landing at the hospital helipad.