What happened
On 19 September 2012, a Robinson R44 Raven II helicopter, registration ZS-HGG, departed Rand Airport for a brief scenic flight. The flight was an unplanned courtesy trip intended to show two visiting South African Police Service officers the airport's perimeter from the air.
While performing a series of climbing turns at approximately 300 ft AGL, the pilot experienced a sudden engine over-speed, noting that the engine RPM indicator had moved off-scale. In an attempt to correct the condition, the pilot closed the throttle, which subsequently caused both the engine and main rotor RPM to decay rapidly. Despite attempting to enter autorotation and flare for a landing, the pilot was unable to maintain control. The aircraft struck an old construction site with significant force, causing the skids to break and the helicopter to roll over. The accident resulted in one serious injury and two minor injuries.
The investigation
SACAA AIID investigators examined the wreckage and the mechanical systems of the Robinson R44 Raven II. The investigation focused on why the engine RPM increased so abruptly and why the rotor RPM decayed so quickly following the pilot's corrective actions.
Technical inspections of the Lycoming engine and the airframe revealed that the engine components, belt tensioners, and fuel systems were all in serviceable condition. No mechanical failures were found in the engine itself. Investigators also noted that the governor switch was found in the "OFF" position following the impact, though the pilot reported the over-speed occurred while the engine was already behaving errily. The investigation also looked into the flight profile, noting that the pilot was operating outside of his scheduled flight plan to accommodate the unplanned passengers.
Findings
- The primary cause of the accident was an unsuccessful forced landing following a rapid decay in main rotor RPM.
- The engine over-speed condition was a significant contributing factor, which occurred during aggressive maneuvering.
- The pilot's decision to execute consecutive left turns at a low altitude of 300 ft AGL was identified as a result of overconfidence and poor handling technique.
- The passengers had not been briefed on emergency safety procedures prior to the flight.
- The aircraft was within weight and balance limits, and the weather conditions were clear and suitable for flight.