What happened
On December 4, 2009, a Robinson R44 helicopter, registration PT-YAS, was performing a flight from Santa Cruz de Monte Castelo to Londrina, Paraná. The flight followed an unplanned overnight stop in the previous day due to deteriorating weather conditions.
While cruising at approximately 2,600 feet, the pilot encountered severe weather, including heavy rain and wind gusts ranging between 23 and 35 knots. During the flight, the engine experienced a sudden RPM surge followed by a significant drop in rotor RPM to below 97%, triggering the low-RPM warning horn. After two subsequent attempts to maintain rotor speed by adjusting the collective, the engine power became insufficient to maintain flight. The pilot initiated an emergency autorotation into unprepared terrain near Fazenda Guedes.
Upon touchdown, the aircraft's skid struck a contour line (curva de nível), causing the helicopter to slide forward and eventually roll onto its left side. The impact caused severe damage to the main rotor, tail boom, tail rotor, windshield, and fuselage.
The investigation
CENIPA's investigation focused on the sequence of events leading to the loss of engine power and the execution of the emergency landing. Investigators examined the aircraft's maintenance records, noting that while the 100-hour inspection was current, the aircraft's logbooks were not up to date.
During the wreckage examination, investigators discovered that the fuel used in the aircraft had been adulterated, which presented a potential cause for the engine power loss. The investigation also analyzed the pilot's flight planning and the execution of the autorotation maneuver. Physical evidence, including the upward bending of the tail boom and the breakage of the tail skid, indicated that the pilot failed to execute a vertical (point) landing, instead allowing the aircraft to move forward across the terrain.
Findings
- The pilot failed to perform an adequate flight plan analysis, proceeding with the flight despite known unfavorable meteorological conditions along the route.
- The pilot's execution of the autorotation maneuver involved an incorrect application of the collective, leading to a forward sliding landing rather than a controlled vertical touchdown.
- The use of adulterated fuel was identified as a factor that may have contributed to the engine failure.
- The pilot's judgment regarding the suitability of a running landing on unprepared terrain was a contributing factor to the severity of the impact.