What happened
On December 31, 2016, a Robinson R44 II helicopter, registration PR-JMP, was conducting a scenic flight near Corinto, Minas Gerais. The aircraft departed from an unregistered area known as Redpoint with a pilot and four passengers. While traversing a mountain range at approximately 2,600 feet, the helicopter encountered turbulence and a 15-knot tailwind.
During the encounter, the aircraft failed to maintain its rate of climb, and the low RPM warning horn activated, indicating the rotor speed had dropped below 97%. The pilot attempted to recover by lowering the collective, but the aircraft continued a descent. The helicopter struck two low-voltage power lines before impacting the ground. The impact caused substantial damage to the aircraft's main rotor, transmission, tail boom, and cabin. The pilot and three passengers were uninjured, while one passenger sustained minor injuries.
The investigation
CENIPA investigators examined the pilot's credentials, the aircraft's maintenance history, and the environmental conditions at the time of the accident. The pilot was highly experienced, with over 932 total flight hours, including 676 hours in the R44 model. The investigation confirmed that the aircraft's airworthiness certificate was valid and that all maintenance logs were up to date.
Weight and balance calculations performed by investigators estimated the takeoff weight at 1,072 kg (2,363 lb), which was within the manufacturer's maximum limits. However, performance charts for the R44 II indicated that, given the altitude of 2,600 feet and a temperature of 34°C, the maximum allowable weight for an out-of-ground-effect (OGE) hover would have been approximately 1,111 kg. The investigation also reviewed Robinson Helicopter Company safety notices regarding high winds, turbulence, and the dangers of low rotor RPM.
Findings
- Adverse meteorological conditions contributed to the loss of performance during the flight.
- The pilot's judgment regarding the decision to fly through turbulent conditions near terrain contributed to the accident.
- The aircraft encountered a loss of lift while flying over mountainous terrain under the influence of turbulence and a tailwind.
- The low RPM warning horn activated, signaling that the rotor speed had fallen below the manufacturer's minimum requirements for powered flight.