TROY, MT, USA
N4069R
Kaman HH-43 B/F
The pilot reported that while in cruise flight, the internal autorotation cockpit gauge needles split, and the helicopter lost altitude. The rotor rpm was decreasing, and the pilot initiated an autorotation. During the descent, the pilot noted that the N1 gauge indicated that the engine was running, but there was no power to the rotor. The helicopter landed hard, which drove the landing gear through the belly and separated the tail boom. A postaccident investigation revealed that bearings in the one-way freewheeling sprag clutch had failed. The one-way clutch was not a time-retireable item, and determining total time of the assembly from the maintenance records was not possible.
On September 23, 1996, at 1700 mountain daylight time, a Kaman HH-43 B/F helicopter, N4069R, registered to and operated by Skyline Helicopters as a 14 CFR Part 91 positioning flight, experienced a low rotor rpm. The pilot initiated an autorotation and landed hard near Troy, Montana. Visual meteorological conditions prevailed at the time and no flight plan was filed. The helicopter was substantially damaged, and the commercial pilot and three passengers were not injured. The two other passengers received minor injuries. The flight had just taken off from a remote location and was en route to an airport in Troy. The pilot reported that he had been operating an external load throughout the day. At the end of the day, the pilot landed to pick up the ground crew. The pilot stated that after takeoff, he ascended to 6,000 feet to look at the next day's logging activity before flying back to Troy. The flight then turned west, still at 6,000 feet, toward Troy. While in cruise flight, the pilot stated that the internal autorotation cockpit gage needles split and the helicopter lost 2,000 feet. The pilot increased throttle and thought that he had a dual tachometer failure. The pilot stated that he pulled in collective and realized that the needles/rotor and N2 tachometers were not married. The rotor rpm was low and the pilot initiated a forced landing. During the descent, the pilot tried to increase rotor with full collective down. Prior to touchdown, the pilot jettisoned the 150-foot-long line into the trees. The pilot stated that the throttle was at full increase, and the N1 indicated that the engine was running, but there was no power to the rotor. The helicopter landed hard, which drove the landing gear through the belly and separated the tail boom. After the landing, the pilot shut down the engine and checked on his passengers. The pilot then climbed on the helicopter and found that the main drive shaft would not freewheel in either direction when rotated manually. After the helicopter was recovered, and during the inspection of the transmission, it was found that the some of the bearings in the one-way freewheeling sprag clutch had failed. Maintenance records for the transmission assembly indicate that the assembly was shipped new, presumably on January 20, 1969, with a total time of zero. The date indicated on the record is written as "20-01-9." The next entry is dated January 16, 1970, and is listed as an inspection of the clutch assembly. The total time of the assembly since 1970 was not listed. The record indicates that the assembly had been removed and installed in several different aircraft throughout its life. The one-way clutch is not listed as a time-retireable item, and determining total time of the assembly from the maintenance records was not possible. The maintenance records indicate that on September 15, 1996, the transmission assembly was overhauled and installed in N4069R. The inspection section of the overhaul manual states that the inspection of the transmission assembly should be performed by a "qualified person with years of experience to correctly interpret visual defects, such as, wear, scuffing, pitting, etc." The manual also states that the bearings shall be thoroughly cleaned and visually inspected for signs of pitting, galling, scoring, flaking, fretting, and excessive wear.
failure of the freewheeling sprag unit bearings for undetermined reasons.
Source: NTSB Aviation Accident Database
Aviation Accidents App
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