What happened
On September 16, 2016, at approximately 20:20 UTC, a Guimbal Cabri G2, registration PR-EFC, was performing a night instructional flight from the EFAI helipad in Contagem, Minas Gerais. The flight was part of a student's training for a Commercial Pilot License.
During the takeoff roll, the aircraft departed with a tailwind on a heading of approximately 320 degrees. Shortly after liftoff, the crew identified a high-voltage power line crossing the departure path, roughly 375 meters away. Realizing the aircraft lacked sufficient altitude to clear the obstacle, the instructor took control and applied increased collective pitch to gain height. While the maneuver successfully cleared the wires, the sudden increase in torque caused the main rotor RPM to drop significantly. This led to a loss of directional control, characterized by a leftward yaw and a spinning motion, causing the aircraft to lose altitude and collide with vegetation and the ground. The two occupants sustained light injuries, while the aircraft suffered substantial damage.
The investigation
CENIPA's investigation focused on the aerodynamic and operational factors leading to the loss of control. Investigators examined the flight profiles of both the instructor and the student, noting that while the instructor was experienced in rotary-wing flight, they had only completed four adaptation flights in this specific model. The student also had limited experience in the Guimological Cabri G2.
Technical analysis revealed that the application of maximum collective pitch reached the engine's power limits (145HP in PWR mode). The resulting torque increase caused the main rotor RPM to decay. Furthermore, the investigation established that the leftward yaw was exacerbated by the tail rotor's reduced effectiveness due to the aircraft's low airspeed and the interference of its own wake. The investigation also noted that the takeoff was performed with a tailwind, placing the aircraft directly toward the obstacle.
Findings
- The takeoff was conducted with a tailwind toward a high-voltage transmission line.
- The crew applied excessive collective pitch to clear an obstacle, exceeding the mechanical power limits of the engine.
- The increase in torque led to a loss of main rotor RPM.
- The aircraft experienced a loss of directional control and entered a spin.
- The instructor's limited experience in the specific aircraft type and the student's low flight hours contributed to the difficulty in managing the emergency.
Safety action
CENIPA issued recommendations to the National Civil Aviation Agency (ANAC) to work with the operator to re-evaluate safety conditions for night operations at the SNHN helipad, specifically regarding the presence of obstacles and the single takeoff/approach axis. Additionally, the operator was advised to review its Safety Management System (SMS) regarding risk management for operations near nearby obstacles.