Rescue Mission and Departure
The helicopter crew had just completed the rescue of a lost hiker and were preparing to return to their base. The pilot informed the flight nurse that dispatch required them to proceed home because the helicopter was due for its 25-hour inspection. However, the pilot indicated that he first needed to return to the location where the hiker had been picked up to obtain an altitude reading. Before takeoff, search and rescue personnel warned the pilot about paragliders in the area. The flight nurse reported that the pilot acknowledged the warning, then took off and proceeded southbound.
Inflight Event
During the climb, the flight nurse heard a loud noise that seemed to come from beneath the helicopter. She heard the pilot exclaim "Oh no," and then the helicopter began spinning clockwise out of control. The flight nurse described being tossed around but attempted to position herself for the crash. The helicopter then impacted the ground.
Post-Impact Observations
After the crash, the flight nurse exited through the front of the helicopter. She checked on the paramedic and the pilot, then retrieved the radio to call for help. She noted that the engines were still running and smelled fuel, and also observed that the tail rotor was missing.
Witness Accounts
Several witnesses on the ground observed the helicopter. They recalled that after takeoff, it made a right turn to proceed south. Some witnesses reported hearing a loud bang. Most described the helicopter performing a 360-degree counterclockwise turn, after which the nose pitched up, the tail rotor separated, and the helicopter continued to spin and descend until it impacted the hillside.
Examination Findings
An examination of the broken tail rotor trunnion revealed four separate fatigue areas originating from the inner splines. The fatigue was attributed to stresses that exceeded the design spectrum. Excessive heating due to friction between the trunnion and blade grip bushings was also noted. The trunnion had a published service life of 2,700 hours; at the time of the accident, it had accumulated 698.0 total hours.