What happened
On April 4, 2009, a Hughes 369HS helicopter departed from the Hartenholm airfield for a scheduled 30-minute commercial sightseeing flight over Hamburg. The flight was accompanied by four passengers. Shortly after takeoff, while the pilot was climbing toward the Hamburg control zone at an altitude of approximately 500–600 ft AMSL, the engine failed. The pilot observed cockpit warning lights and heard the rotor speed warning horn.
In response to the emergency, the pilot immediately initiated an autorotation and attempted to locate a suitable landing site. The pilot identified a fenced pasture directly in the flight path as a potential landing area. While attempting to clear the fence, the aircraft's airspeed and main rotor RPM decreased significantly. At an altitude of approximately 3 meters, the helicopter lost lift and struck the ground in a nose-up attitude, subsequently flipping forward. The impact caused the tail boom to break off, and the fuselage came to rest on its right side. The pilot managed to exit the wreckage independently and assisted the passengers in evacuating. The accident resulted in two serious injuries and three minor injuries.
The investigation
The BFU examined the wreckage and the engine components. The investigation included a detailed inspection of the Allison 2D-C18A turboshaft engine, the transmission, and the fuel system. Investigators analyzed fuel samples and performed a test bench run of the engine. The investigation also reviewed the pilot's training records, which showed recent proficiency training in autorotative maneuvers, and checked the aircraft's maintenance history and weight and balance status.
Findings
- The engine failure occurred during a critical phase of flight (climb-out) at a low altitude, leaving very little time to execute the emergency procedure.
- While fuel samples showed levels of "existent gum" exceeding specifications, investigators determined this could not have caused the engine failure, as the fuel filters and nozzles were clean and the engine produced sufficient power during testing.
- The aircraft was within its weight and center of gravity limits, and the maintenance status was current.
- The autorotation was terminated at too high an altitude, leading to a loss of rotor RPM and airspeed that made the subsequent loss of lift and uncontrolled descent unavoidable.
- The presence of the fence on the chosen landing site hindered the landing maneuver, contributing to the loss of rotor energy.