What happened
On May 5, 2013, a Hughes 269C helicopter, registration CS-HAZ, departed from Cascais Airfield (LPCS) for a dual-command training flight. The flight, operated by Aerocondor, S.A., was intended to practice autorotation procedures by simulating an in-flight engine failure.
At approximately 09:15 UTC, while flying over the Sado estuary, the crew reduced engine power to simulate an engine-off configuration. During this maneuver, the engine unexpectedly stopped producing power. The instructor pilot attempted to restart the engine without success and initiated an emergency landing at a pre-selected area of sparse pine forest.
During the short final approach, the instructor pilot encountered trees in the flight path. To clear the obstacle, the pilot increased the collective pitch, which caused a reduction in airspeed and a loss of main rotor kinetic energy. The subsequent landing was violent due to the low-energy state of the rotor. During the impact, a main rotor blade struck and fractured the tail, causing the helicopter to rotate out of control and come to rest nearly in an inverted position. There were no injuries to the two occupants.
The investigation
The GPIAAF conducted a safety investigation to identify the causes of the event. The investigation included a wreckage assessment, where the Lycoming HIO-360-D1A engine was sent to an authorized service center for analysis. Both visual inspections and bench testing of the engine revealed no anomalies or mechanical failures that could justify the engine stoppage.
Findings
- The engine failure was likely triggered by rapid reductions in the power lever, a known risk for this aircraft model. The FAA had previously issued a Special Airworthiness Information Bulletin (SW-12-12) advising operators that sudden movements of the power lever in these engines could result in unintentional engine shutdowns.
- The instructor pilot's attempt to clear trees during the landing phase led to an increase in pitch, depleting the kinetic energy required for a smooth touchdown.
- The aircraft sustained substantial damage to the tail and main rotor blades, along with significant deformations to the primary structure.
- The flight crew, consisting of a 34-year-old instructor and a 20-year-old student, were both properly licensed and medically certified at the time of the accident.