Incident Description
During a landing attempt, the pilot of a Robinson R-44 helicopter found that he could not apply left cyclic control. He executed a run-on landing using right turns, completing the landing without further incident.
Findings
Examination after the flight revealed that the lateral trim actuator shaft had worn and become lodged in the guide bearing, interfering with the surrounding structure. The inspection criteria for the lateral cyclic trim system in place at the time did not include a measurement of shaft wear. A service bulletin, SB-19, addressed excessive shaft wear on Robinson R-44 helicopters but was not applicable to the incident helicopter.
Corrective Actions
Following this incident, a new service bulletin, SB-26, was released for R-44 helicopters. It specified that the lateral cyclic trim assembly shaft, part number C585-1, should be measured in several places. If the shaft diameter varied more than 0.004 inches in any 0.50-inch length, the assembly was to be replaced before further flight. Subsequently, a priority Airworthiness Directive, AD 98-04-12, was issued mandating compliance with the terms of SB-26.