What happened
On August 1, 2017, at approximately 18:15 UTC, an MD900 (902 Config) Explorer helicopter was engaged in a HEMS (Helicopter Emergency Medical Service) mission near the Grossglockner in Carinthia, Austria. The flight was dispatched from Matrei to the Erzherzog-Johann-Hütte to attend to a medical emergency.
Upon arrival at the site, which was at an altitude of approximately 3,420 meters (11,220 ft), the pilot performed a hover check to verify performance. Due to the lack of a suitable landing area, the pilot opted to position the helicopter in a hover, supported by the right skid, to facilitate the loading of the patient. The patient was transferred into the aircraft with the assistance of the crew and a local mountain rescuer.
During the departure phase, the aircraft began to rotate clockwise around its high axis. The pilot was unable to regain control and subsequently reduced the collective pitch. The helicopter completed several rotations before impacting the ground near the landing site, eventually tipping onto its right side. The impact caused heavy damage to the aircraft, though the crew members sustained only minor injuries.
The investigation
The Austrian SUB investigation reconstructed the flight sequence using statements from the pilot, medical crew, and witnesses, alongside police reports and private video recordings. The investigation examined the aircraft's technical condition, including the NOTAR (No Tail Rotor) system, the aerodynamic effects of the ground effect at high altitude, and the environmental conditions at the time of the accident.
Findings
- The primary cause of the accident was a loss of control during the takeoff phase.
- The aircraft was operating near the limits of its aerodynamic controllability.
- The unique aerodynamic characteristics of the NOTAR system, specifically regarding how it interacts with ground effect compared to conventional tail rotors, contributed to the loss of directional stability.
- The high altitude and specific environmental conditions at the Grossglockner summit played a role in the flight dynamics during the maneuver.