What happened
On December 4, 2014, at approximately 10:50 UTC, a Schweizer 269C-1 helicopter, registration CS-HFD, was conducting a flight training mission near the Ponte de Sôr airfield in Portugal. The aircraft, operated by Escola de Aviação Aerocondor, was carrying an instructor and a student pilot.
After approximately one hour of flight operations in a designated training area, the helicopter crashed into an open field characterized by low vegetation and no significant obstacles. The aircraft struck the ground with a high rate of descent and very low forward speed. There were no survivors, and the impact resulted in the total destruction of the aircraft.
The investigation
The GPIAAF investigation was limited by the lack of survivors and witnesses at the scene. Investigators examined the wreckage, analyzed the aircraft's maintenance records, and reviewed flight manuals. The investigation revealed that the aircraft's flight manual had not been updated to include a 2012 revision from the manufacturer, a discrepancy that was also found in other helicopters within the operator's fleet.
Technical analysis focused on the engine and rotor performance during the final moments of flight. The investigation established that the helicopter hit the ground with near-zero horizontal speed and critically low engine and rotor RPM. Additionally, it was noted that the crew had limited experience flying in atmospheric conditions conducive to carburetor icing, and that standard procedures for checking idle mixture and idle speed were not being performed according to manufacturer specifications.
Findings
- The flight was properly authorized and the instructor was appropriately qualified.
- The aircraft was airworthy, with valid documentation and a compliant maintenance program.
- The aircraft's mass and balance were within normal operating limits.
- The crew lacked sufficient experience operating in conditions prone to carburetor ice formation.
- The helicopter entered a dangerous state involving overpitch, which led to a loss of rotor RPM.
- The aircraft was operating within the dangerous boundaries of the Height/Velocity (H/V) diagram.
- The crew was unable to execute a safe autorotation to the ground.