Accident Overview
On October 20, 2014, at approximately 07:00 local time, a Eurocopter SE 313B Alouette II helicopter, registration TU-TRM, was conducting an agricultural spraying mission over banana plantations owned by Société CANAVESE in Aboisso, Côte d’Ivoire. The flight was a single-pilot operation under visual meteorological conditions with a temperature of 27°C.
Flight Sequence
The pilot, a 53-year-old male with 3,700 total flight hours (1,400 on type), performed a normal pre-flight inspection and engine start. After takeoff, the ground mechanic observed the helicopter begin to pivot to the left and then spin on its vertical axis several times. According to the mechanic, the aircraft executed approximately five uncontrolled autorotations before crashing on muddy terrain about 30 meters from the takeoff point. The helicopter immediately tipped onto its right side; the main rotor blades struck the ground and stopped quickly. The pilot, uninjured, evacuated the helicopter without assistance through the left door. No fire occurred. The helicopter sustained substantial damage.
Investigation Findings
Examination of the wreckage, reassembled at the operator’s base in Abidjan, revealed a bent tail boom that had caused the disconnection of the two drive shafts, resulting in a loss of tail rotor drive. After straightening the tail boom, the shafts reconnected without force. The tail rotor control system was reassembled, and no anomalies were found in the pedal control runs. However, measurement with a local template on an undamaged tail rotor blade showed that the pedal travel range between left and right stops was 20° of pitch change, whereas the manufacturer required a minimum of 23°. This meant a deficit of approximately 3° of pitch on the right pedal. Consequently, the pilot did not have full anti-torque authority to counter the main rotor torque, especially with a takeoff mass close to the maximum takeoff weight (1,565 kg vs. MTOW of 1,600 kg). The helicopter’s center of gravity was at the aft limit. The engine showed no evidence of failure; borescope inspection only found some mud in the air intake.
Pilot Testimony
The pilot stated that after a normal lift-off, the helicopter began to yaw to the left despite full right pedal input. The rotation continued, and after several revolutions, he decided to land quickly. As the skids touched the muddy ground, the helicopter tipped onto its right side.
Probable Cause
According to the investigation report, the accident resulted from a loss of control of the helicopter shortly after takeoff, probably due to a loss of anti-torque function caused by insufficient pitch on the right pedal (approximately 3° less than required) to counter the maximum torque of the main rotor. The takeoff mass near the maximum takeoff weight may have been a contributing factor.