What happened
On 27 February 2009, a Robinson R44 Raven II helicopter, registration ZS-KTM, departed Rand Aerodrome for a private flight to Ermelo. While flying at an altitude between 300 and 500 feet above ground level over a residential area, the pilot experienced an engine over-speed condition, noting that the RPM gauge had reached the red line.
The pilot contacted OR Tambo International control tower to report the engine over-revving and declared his intention to return to Rand Aerodrome. During the attempt to execute a precautionary landing in a grass field adjacent to the N17 highway, the aircraft entered an excessive nose-up attitude. This caused the tail rotor blades, tail stinger, and lower vertical fin to strike the ground, resulting in the tail rotor assembly breaking off. The helicopter subsequently struck a water culvert and came to rest on its side. Both occupants sustained serious injuries.
The investigation
SACAA AIID investigators examined the wreckage and the flight history of the pilot. The investigation confirmed that the helicopter was flying within its weight limits at the time of the accident. Witnesses on the highway observed the aircraft flying low and noted the unusual rotation of the main rotors before the impact.
Investigators also reviewed the pilot's training records. While the pilot had received training regarding "governor off" emergencies during his initial student pilot phase, there was no evidence that he had been subjected to such emergency evaluations during his subsequent license renewal tests. The investigation also noted that the pilot was not wearing a helmet, which may have contributed to the severity of his head injury.
Findings
- The primary cause of the accident was an unsuccessful precautionary landing following an in-flight engine over-speed condition.
- The tail rotor assembly separated from the airframe due to ground impact during the landing flare.
- The pilot's lack of recent, specific training/evaluation regarding governor failure procedures contributed to the difficulty in managing the emergency.
- The absence of protective headgear likely increased the level of injury sustained by the pilot.