Primary finding
Probable cause
The pilot's improper liftoff technique, which resulted in ground resonance, and the pilot's delayed recognition of the ground resonance.
Investigator assessment
Analysis narrative
The helicopter began to vibrate as the pilot raised the collective for liftoff. The pilot lowered the collective and closed the throttle when the vibration began; however, he was too late in recognizing the onset of ground resonance, which resulted in a violent, uncontrollable oscillation and separation of the tail boom from the fuselage. Examination of the helicopter revealed no anomalies that would have precluded normal operation.
Source record
Factual narrative
On April 17, 2012, about 1116 central daylight time, a Hughes 269A, N69HJ, experienced ground resonance during takeoff at Grinnell Regional Airport (GGI), Grinnell, Iowa. The pilot subsequently aborted the takeoff. The commercial pilot and a passenger were uninjured. The helicopter sustained substantial damage to the fuselage. The helicopter was registered to Lowry Flying Service Inc and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed and a flight plan had not been filed for the local flight that was originating at the time of the accident. The pilot stated that when he raised the collective for liftoff, the helicopter started to vibrate. He "rolled the collective down" and "throttle off," but it was too late, and the helicopter shook apart "immediately." The transmission broke severing the tail. The rotor blades hit the ground. According to the Federal Aviation Administration inspector, the helicopter never lifted off the ground during the accident flight. The pilot experienced ground resonance on three previous flights, the first of which was during takeoff and the other two occurred during landing. During the previous three occurrences of ground resonance, the pilot was able to identify and initiate a successful recovery. During the accident flight, the pilot was too late in recognizing the onset of ground resonance. There were no mechanical anomalies that would have precluded normal operation.