Gustine Airport, Gustine, CA

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Airport Area Accident History:
Accident occurred Wednesday, May 11, 2005 in Gustine, CA
Probable Cause Approval Date: 8/29/2006
Aircraft: Robinson R44, registration: N144SM
Injuries: 2 Uninjured.
The helicopter landed hard and rolled over after the nut/bolt assembly connecting the left cyclic push-pull tube to the swashplate came loose, causing a loss of roll control during takeoff. No mechanical anomalies were noted during the preflight. The certificated flight instructor (CFI) and student departed to do training at another airport. During takeoff to return to their home base, the CFI heard a clicking noise coming from the helicopter and decided to make a precautionary landing; however, the helicopter began a roll to the right. The CFI attempted to correct the roll to the right with the application of left cyclic, but there was no corresponding response. The right skid contacted the ground and the helicopter rolled over, coming to rest on its left side. Following the accident, the bolt, nut, and two spacers that connected the left cyclic push-pull tube to the swash plate were located on the runway. When the Federal Aviation Administration inspector arrived, he also walked the accident area and found the self-locking nut. A review of the aircraft logbook indicated that the left rib at the top of the mast fairing had been installed at the last 100-hour inspection, 2.5 hours before the accident. In order to remove the left rib (bulkhead), the bolt and nut assembly that attaches the left cyclic push-pull tube to the left lug of the non-rotating swash plate had to be disassembled, and then reassembled after the rib (bulkhead) replacement. According to the manufacturer's Illustrated Parts Catalog, left cyclic push-pull tube connection to the non-rotating swash plate assembly requires a bolt and self-locking nut, 3 spacers (2 of the 3 spacers were found at the accident site), a washer, and a locking pal-nut, were not found. A metallurgical examination of the swash plate assembly, left push-pull tube, left rib (bulkhead), nut and bolt and associated hardware was conducted. All of the fracture surfaces examined revealed no preexisting damage. The absence of the bolt between the left cyclic push-pull tube and the non-rotating swash plate after the accident and the thread imprints within the hole of the left lug of the non-rotating swashplate indicated that the bolt had been backing out of the hole over time. The bolt and nut that were recovered were in good condition, and the hole in the left lug of the non-rotating swash plate was not significantly ovalized, indicating that the bolted connection was not subjected to excessive loads of any kind. The loss of the nut (and subsequent backing out of the bolt) indicates that the connection was not properly assembled following the recent maintenance, which required the bolted connection to be disassembled. The National Transportation Safety Board determines the probable cause(s) of this accident as follows: the improper installation of the nut/bolt assembly connecting the left cyclic push-pull tube to the non-rotating swashplate by maintenance personnel, which led to a loss of roll control during takeoff.

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