What happened
On October 10, 2009, a Robinson R22 Beta helicopter, registration PT-YDW, was conducting a local flight instruction mission at the Belém Novo Aerodrome in Porto Alegre, Brazil. The flight, operated by Aeroclube do Rio Grande do Sul, involved an instructor and a student pilot practicing approach and landing procedures for autorotation.
During a go-around maneuver, the low rotor RPM warning horn sounded, indicating that the main rotor speed had dropped below 97%. The student pilot had inadvertently reduced engine power while attempting to reposition the rubber protection on the collective lever. In response to the alarm, the student attempted to recover the RPM by lowering the collective, but the warning persisted. Believing the aircraft was experiencing an engine failure, the instructor took control of the aircraft and initiated an emergency landing procedure. The helicopter performed a left turn to return to the runway and landed on the grass adjacent to runway 26. The landing was abrupt, resulting in light damage to the tail cone, but both occupants remained uninjured.
The investigation
CENIPA's investigation focused on the sequence of events leading to the low RPM warning and the subsequent decision-making process. Investigators examined the aircraft's maintenance records, noting that while the airworthiness certificate was valid, the engine and airframe logbooks were not up to date. The investigation also reviewed the flight crew's credentials, confirming that both pilots held valid licenses and medical certificates.
Technical analysis of the flight dynamics revealed that the engine and aircraft systems showed no signs of mechanical failure. Instead, the investigation centered on the crew's interaction and the physical actions taken during the critical phase of the go-around. The investigation established that the reduction in power was a direct result of the student's manual interference with the collective lever's protective cover.
Findings
- The low rotor RPM was caused by the student pilot inadvertently reducing power while adjusting the rubber protection on the collective lever.
- A breakdown in cockpit coordination and communication prevented the instructor from realizing the power reduction was due to pilot input rather than a mechanical engine failure.
- The instructor's situational awareness was diminished, which prevented the timely identification of the student's error and hindered the implementation of appropriate corrective measures.
- Ineffective crew resource management and impaired decision-making contributed to the mismanagement of the emergency situation.