Edgerton, IN, USA
N9561F
HUGHES 269B
The pilot reported a vibration in the helicopter antitorque pedals and a subsequent loss of directional control. The pilot initiated an autorotation to a field, and the helicopter sustained damage to the left landing skid and fuselage. A postaccident examination revealed that the tail rotor drive shaft failed due to an overstress fracture that resulted from contact with the tailboom bulkhead. Examination of the tailboom support structure was unable to determine the underlying cause of the contact between the tailboom and drive shaft. The operator reported that he was not aware of any events prior to the accident that would have compromised the tailboom support structure.
On April 29, 2011, about 1930 eastern daylight time, a Hughes 269B, N9561F, experienced an in-flight loss of directional control and the pilot executed an autorotation to a field near Edgerton, Indiana. The pilot reported no injuries. The helicopter sustained substantial damage to the fuselage. The aircraft was registered to and operated by Heartland Helicopters, LLC, under the provisions of 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed for the flight, which operated without a flight plan. The local flight originated from a field near Edgerton, Indiana, about 1900. The pilot had reportedly finished spraying a field and was about 30 feet above ground level (agl) when he felt a vibration in the antitorque pedals. The helicopter subsequently started to yaw and rotated 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. A postaccident examination revealed that the tail rotor drive shaft failed at the forward end of the tail boom, where the drive shaft passed through the tail boom bulkhead. Metallurgical examination determined that the drive shaft was deformed inward at the fracture, and the paint was cracked and flaked off 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. A postaccident visual examination of the fuselage aft cluster fittings did not reveal any anomalies. The fittings appeared to be intact and the mating struts securely attached. One tail boom support strut was fractured midspan; however, 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. At the time of the accident, the helicopter had accumulated about 4,454 hours total time. Maintenance records indicated that the most recent annual inspection was completed on March 16, 2011, at 4,428.3 hours. The tail rotor drive shaft was installed on the helicopter in December 1997. At the time of the accident, it had accumulated about 2,648 hours. The operator stated that 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. The operator noted that prior to the annual inspection, a pilot noted paint chipping from the drive shaft at the location the shaft passed through the tail boom bulkhead. Further examination by a mechanic did not reveal any damage to the drive shaft itself 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.
A loss of clearance between the tail rotor drive shaft and the tailboom bulkhead for undetermined reasons, which resulted in the overstress failure of the drive shaft.
Source: NTSB Aviation Accident Database
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