What happened
On April 11, 2002, a BK-117 C-1 helicopter, registration PT-YSP, was conducting a flight instruction session near the Guarapiranga Reservoir in São Paulo, Brazil. The flight was part of a training program for a newly hired pilot, accompanied by an instructor and a passenger.
The crew was performing a specific maneuver: a single-engine failure simulation from a hover out of ground effect (OGE). During the exercise, the aircraft experienced a significant drop in main rotor RPM (NR). The student pilot failed to promptly implement the necessary control inputs—specifically reducing collective pitch and establishing a nose-down attitude to gain airspeed—to maintain rotor inertia and flight parameters.
As the rotor RPM dropped below 90%, the instructor took control to attempt a recovery by pitching the aircraft down. However, the aircraft was already in an unrecoverable state with a high rate of descent. The helicopter struck the ground in a nose-high attitude, approximately 200 meters from the start of the maneuver. The impact caused the tail boom to separate, the main rotor to disintegrate, and the aircraft to slide and capsize. The instructor escaped uninjured, while the student pilot and the passenger sustained minor injuries.
The investigation
CENIPA investigators examined the wreckage and the operational procedures of the operator, Aeromil Táxi Aéreo Ltda. The investigation focused on the mechanical state of the engines and the effectiveness of the training program.
Analysis of the engine power shafts revealed that the engine not intentionally reduced was operating at high power, evidenced by a broken power shaft due to torsion upon impact. Conversely, the engine that had been intentionally reduced to idle showed no such damage, indicating it was producing low power. The investigation also noted that the training program was conducted intermittently during operational downtime, with the instructor also managing significant administrative and supervisory responslegilities.
Findings
- The primary cause of the accident was the failure to promptly apply the necessary control inputs (nose-down attitude and collective reduction) to maintain rotor RPM during the single-engine failure simulation.
- The student pilot's delay in commanding the necessary pitch and the high collective pitch applied resulted in an excessive load on the rotor, preventing the maintenance of sufficient RPM.
- The training program lacked a progressive approach to managing the high workload and physiological stress associated with such complex maneuvers.
- Operational deficiencies included inadequate supervision of flight activities and a training structure that did not provide dedicated time or aircraft for instruction, often interrupting training for emergency medical missions.
- The instructor's heavy administrative workload and the lack of a formal, continuous training syllabus contributed to the lack of prepared responses for the student's psychomotor errors.