Accident Overview
On April 29, 2011, about 1930 eastern daylight time, a Hughes 269B, registration N9561F, experienced an in-flight loss of directional control during an aerial application flight under 14 CFR Part 137. The pilot executed an autorotation to a field near Edgerton, Indiana. The helicopter sustained substantial damage to the fuselage; the pilot reported no injuries. Visual meteorological conditions prevailed, and the flight operated without a flight plan.
Sequence of Events
The local flight originated from a field near Edgerton about 1900. The pilot had finished spraying a field and was approximately 30 feet above ground level when he felt a vibration in the antitorque pedals. The helicopter subsequently began to yaw and completed one full revolution before the pilot initiated an autorotation to a field. The helicopter came to rest upright with damage to the left landing skid and fuselage.
Postaccident Examination
A postaccident examination revealed that the tail rotor drive shaft failed at the forward end of the tail boom, where it passed through the tail boom bulkhead. Metallurgical examination showed the drive shaft was deformed inward at the fracture with cracked and flaked paint on the outer surface. Circumferential paint transfer was observed on the drive shaft in a color and shade matching the tail boom bulkhead. The fracture surface exhibited features consistent with overstress fracture that progressed under rotating bending stresses.
Visual examination of the fuselage aft cluster fittings revealed no anomalies; the fittings appeared intact with securely attached mating struts. One tail boom support strut was fractured midspan, but the fracture appeared consistent with overstress failure due to the hard landing after the autorotation. Continuity of the tail rotor transmission was confirmed through simultaneous rotation of the aft drive shaft section and the tail rotor blades. The drive shaft-to-transmission input splines appeared intact.
Maintenance History
At the time of the accident, the helicopter had accumulated about 4,454 hours total time. The most recent annual inspection was completed on March 16, 2011, at 4,428.3 hours. The tail rotor drive shaft was installed in December 1997 and had accumulated about 2,648 hours. The operator stated he was not aware of any hard landings or other events that might have compromised the tail boom support structure prior to the accident, and brought the tail boom into contact with the drive shaft. Prior to the annual inspection, a pilot noted paint chipping from the drive shaft at the location where it passed through the tail boom bulkhead. Further examination by a mechanic did not reveal damage to the drive shaft, and the helicopter was returned to service. According to the operator, pilots who flew the helicopter after the annual inspection did not report any anomalies related to the tail boom or drive shaft.