What happened
On September 10, 2010, a Hughes 269C helicopter, registration CS-HAZ, operated by GESTAIR Flying Academy, was conducting a flight training mission. The aircraft departed from Cascais Municipal Aerodrome (LPCS) carrying an instructor and a student pilot, heading toward the Barrosinha runway in Alcáender do Sal.
During the flight, the instructor initiated a demonstration of an engine failure at takeoff. While at an altitude of approximately 80 feet AGL and a forward speed of 60 mph, the instructor reduced engine power to simulate the failure. The crew attempted to perform an autorotation maneuver to land ahead of the aircraft. However, during the flare phase, the rotor RPM had dropped significantly to approximately 250 RPM, well below the normal operating range of 390–504 RPM. Due to the low altitude and insufficient rotor speed, the aircraft could not generate enough lift to arrest the rate of descent, resulting in a violent impact with the center of the runway.
The left skid struck the ground first, absorbing much of the impact energy but ultimately fracturing the landing gear supports. The aircraft came to a rest on the side of the runway. There were no injuries to the two occupants, though the aircraft sustained grave damage.
The investigation
The GPIAAF investigation examined the flight parameters and the technical feasibility of the maneuver. Investigators analyzed the aircraft's altitude and airspeed at the moment the engine power was reduced. By comparing these values against standard manufacturer recovery diagrams, the investigation determined that the aircraft was operating within an unsafe envelope where a successful recovery without engine power was compromised from the start.
Findings
- The instructor's decision to simulate an engine failure at 80 feet AGL and 60 mph was unsafe, as the aircraft had not yet reached the minimum required velocity for a successful recovery.
- The reduction of engine power prevented the necessary re-coupling of the rotor and engine.
- The rotor RPM dropped to approximately 2'250 RPM, which was insufficient to create the lift required to sustain the descent during the flare.
Safety action
- The GPIAAF recommended that GESTAIR Flying Academy select training areas for practicing autorotations that preferably feature soft terrain, such as areas near water or marshlands. Such surfaces can better absorb impact energy and allow the skids to slide, minimizing the risk of structural damage during hard landings.