Waynesboro, GA, USA
N5211R
Hughes HU-369-D
The flight was contracted by Georgia Power Company to complete inspections and maintenance on a number of their transmission power lines. After completing a shield wire splice procedure, both the pilot and passenger heard a "pop" in the rear of the helicopter. The helicopter began to spin "hard to the right". However, to avoid hitting the shield wire, the pilot increased the collective pitch, which accelerated the turn. After clearing the shield wire and making the second turn, the pilot reduced the throttle to slow the spin, leveled the helicopter and collided with trees in a level flight attitude. The pilot did not report any mechanical malfunctions with the helicopter prior to the accident. Examination of the helicopter revealed the main rotor blades separated, the left skid separated, the windshield broken, upward crush damage along the bottom of the fuselage aft of the skid, the tail rotor assembly separated at driveshaft, crush damage along the sides of the tail section and the horizontal stabilizer detached from the tail. The tail rotor assembly and part of the tail rotor drive shaft were sent to the NTSB Materials Laboratory in Washington D.C. for further examination. The Materials Lab determined that the tail rotor assembly failed due to a fatigue fracture of the input gearshaft in the tail rotor gearbox assembly. This fracture led to jamming of the gearbox and the resulting overstress fracture of the tail rotor drive shaft, which was consistent with the engine driving the shaft at the forward end with the aft end stopped.
On September 10, 2004 at 1250 eastern daylight time a Hughes HU-369-D, N5211R registered to Helibase LLC and operated by Haverfield Corporation collided with trees while conducting power line maintenance in Waynesboro, Georgia. The aerial observation flight was operated under the provisions of Title 14 CFR Part 133. Visual meteorological conditions prevailed and a company visual flight rules flight plan was filed. The helicopter was substantially damaged. The pilot and passenger received minor injuries. The flight originated from Daniel Field in Augusta, Georgia, on September 10, 2004 at 0730. The flight was contracted by Georgia Power Company to complete inspections and maintenance on a number of their transmission power lines. After completing a shield wire splice procedure, both the pilot and passenger heard a "pop" in the rear of the helicopter. The pilot stated that the helicopter began to spin "hard to the right". However, to avoid hitting the shield wire, the pilot increased the collective pitch, which accelerated the turn. After clearing the shield wire and making the second turn, the pilot reduced the throttle to slow the spin, leveled the helicopter and collided with trees in a level flight attitude. Examination of the helicopter revealed the main rotor blades separated, the left skid separated, the windshield broken, upward crush damage along the bottom of the fuselage aft of the skid, the tail rotor assembly separated at driveshaft, crush damage along the sides of the tail section and the horizontal stabilizer detached from the tail. The pilot did not report any mechanical malfunctions with the helicopter prior to the accident flight. The tail rotor assembly and part of the tail rotor drive shaft were sent to the NTSB Materials Laboratory in Washington D.C. for further examination. The Materials Lab examination revealed the tail rotor drive shaft was fractured at two locations and one of the tail rotor blades were bent inboard near the blade root. Both fracture locations on the tail rotor drive shaft showed bending or twisting consistent with overstress fractures. The tail rotor blades had different part numbers indicated on their identification plates. The bent blade had 33 spacers on the pitch change link attachment stud which weighed a total of 34 grams. Both the weight and number of these spacers substantially exceeded limits stated in the Tail Rotor Balance Maintenance Procedures in the Maintenance Manual published by MD Helicopters. The two blades were removed from the hub and weighed with the pitch change link weights removed but the tip weights in place. The straight blade weighed 994 grams and the bent blade weighed 1017 grams. The gearbox housing was disassembled. The input gearshaft was fractured and the interior of the gearbox housing had gouges and scrapes and the housing was cracked at the input opening. Also, the gear teeth for the output gearshaft was damaged around the circumference. Continuing the disassembly, the oil seal and housing pieces were removed. The shims, which rested on the forward side of the oil seal as it was removed, were heavily beated and deformed with substantial thinning in the contact areas between the flex coupling and the spacer. The input gearshaft bearing outer race had a milky track with small pits on the raceway surface. The washer located aft of the input gearshaft bearing had pitting consistent with fretting on both its forward and aft faces. After removal of the washer, bearing and spacer from the input gearshaft, pitting consistent with fretting contact was observed on portions of the forward face of the gearshaft disk where it had contacted the washer. The fracture features on most of the visible fracture surface of the input gearshaft, were relatively smooth with curving arrest lines consistent with fatigue. The origin area of the fatigue cracking was not on the exposed fracture, but the fatigue features emanated from a crack located in the fillet between the disk and shaft portions of the input gearshaft. A review of maintenance records for the input gearshaft revealed that the assembly had a total of 3,135.2 flight hours at the time of the fatigue failure. The tail rotor transmission was last overhauled on April 14, 2003 at 1,478.8 flight hours.
The tail rotor assembly failed due to a fatigue fracture of the input gearshaft in the tail rotor gearbox assembly, which resulted in a loss of tail rotor control and subsequent collision with trees.
Source: NTSB Aviation Accident Database
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