What happened
On July 31, 2013, a Schweizer 269C-1 helicopter, registration PR-MIL, was conducting a pilot transition training flight over the Guarapiranga Reservoir in São Paulo, Brazil. The flight, operated by the São Paulo Military Police (GRPAE), involved two crew members performing simulated autorotation exercises under VFR conditions.
During the fourth simulated autorotation of the session, the crew initiated the recovery maneuver. As the pilot attempted to apply power using the twistgrip collective, the engine failed to respond with the expected increase in power. In an attempt to manage the descent, the instructor executed a flare with a significant nose-up attitude. Consequently, the tail boom struck the surface of the water, resulting in substantial damage to the tail cone and the blades of both the main and tail rotors. Both crew members escaped the aircraft uninjured.
The investigation
The investigation conducted by CENIPA examined the mechanical state of the aircraft and the flight procedures used during the training. Technical inspections of the engine and debris analysis by the Aeronautical Institute and Space (IAE) ruled out any mechanical malfunction or engine failure. The investigation confirmed that the aircraft was airworthy, within weight and balance limits, and that the crew held valid medical and technical certifications.
Investigators noted a discrepancy between the flight school's training procedures and the manufacturer's manual. While the Schweizer 269C-1 Pilot's Flight Manual recommends maintaining engine RPM at 2,500 RPM to prevent irregular operation during recovery, the training school's guidelines instructed instructors to maintain engine RPM between 2,000 and 2,400 RPM. The crew reported that the engine RPM had been reduced to below 2,000 RPM prior to the start of the recovery.
Findings
- Improper application of controls: The investigation suggested that the rapid rotation of the twistgrip may have occurred without the corresponding expected power increase.
- Pilot experience: The limited experience of the pilot contributed to the outcome.
- Pilot judgment: Errors in flight judgment during the maneuver contributed to the impact.