What happened
On 11 June 2006, a Robinson R22 helicopter, registration ZS-RMJ, was conducting a private VFR flight from Grand Central Aerodrome. While flying straight and level over the Sandton City area, the pilot observed the clutch light remaining illuminated for longer than the manufacturer's recommended eight-second limit.
Following established flight manual procedures, the pilot pulled the circuit breaker and initiated an autorotation. Although an open field was visible ahead, the presence of power lines forced the pilot to maneuver to the left, ultimately executing a forced landing on a tarred street in the Sandown suburb of Johannesburg. During the descent, the main rotor blades struck a tree, leading to a hard landing. The aircraft bounced several times and skidded approximately 50 metres before coming to a halt. There were no injuries to the pilot or the passenger, though the aircraft sustained damage to the skids, the cross tube, and the main rotor blades.
The investigation
SACAA AIID investigators examined the mechanical state of the aircraft and its maintenance history. The investigation focused on the clutch actuator assembly and the recent maintenance performed on the airframe. The aircraft had completed its last major inspection (MPI) approximately 16 days prior to the incident.
Technical analysis of the wreckage revealed that the lower bearing on the clutch actuator was in the early stages of failure. Specifically, the axial play was measured at 0.012", exceeding the maximum allowable limit of 0.010". Furthermore, investigators found evidence of a damaged seal and high temperature readings on the Telatemp indicators. Maintenance records indicated that while the upper bearing had been regularly lubricated, the lower bearing had not been greased since April 2006.
Findings
- The primary cause of the incident was the failure of the clutch actuator due to insufficient lubrication.
- The pilot correctly followed emergency procedures by pulling the circuit breaker and entering autorotation after the clutch light exceeded the safety threshold.
- The hard landing was necessitated by the need to avoid overhead power lines during the emergency descent.
- The investigation noted that the lower actuator bearing is difficult to access, which may have contributed to the uneven lubrication between the upper and lower bearings.
- There was evidence of heat-related discolouration on the Telatemp indicators, suggesting that the bearing temperature had been rising prior to the incident.
Safety action
- It is recommended that pilots, operators, and maintenance staff increase their focus on examining bearing cooling scrolls for any signs of heat discolouration.
- Maintenance personnel and pilots should perform thorough inspections of all Telatemp indicators during pre-flight and scheduled maintenance, with particular attention paid to the lower actuator bearing.
- Operators should maintain detailed monitoring records to track temperature trends and ensure that any identified discrepancies are addressed by a maintenance engineer before further flight.