Incident Description
On August 4, 2010, at 0645 central daylight time, a Bell Helicopter Textron 430 (registration N430CM) was on the ground at ground idle power while conducting the engine start checklist. During the procedure, the collective control moved to the full up position. The pilot was unable to lower the collective, and subsequently the helicopter's engines were shut down. The pilot and seven passengers disembarked normally. The flight was operated under Title 14 CFR Part 91 and was intended to fly to an oil rig platform off the coast of Louisiana. No injuries were reported among the passengers and crew.
Investigation Findings
Further inspection of the aircraft revealed that the main rotor collective servoactuator piston rod had fractured. No other airframe damage was noted. The collective servo actuator (part number 222-382-001-107, serial number HHR552A) was examined in Bell Helicopter Textron's Field Investigations Laboratory. According to Bell, the servo actuator piston rod was found to be fractured as a result of stress corrosion cracking at approximately the second thread from the output piston, which was also the location of the first thread of the nut. The examination also determined that debris was present on the piston rod nut and output piston interface and that nearly all of the vacuum deposited cadmium coating had been consumed.
Service Actions
In response to this incident, Bell Helicopter Textron issued a number of alert service bulletins. Alert Service Bulletin 430-10-44 was issued on August 18, 2010, advising operators to perform a one-time inspection of the servo actuator piston rod prior to further flight. A ferry flight of up to 5 hours was permitted to return the aircraft to appropriate maintenance facilities. This service bulletin applied only to servo actuators manufactured by Woodward HRT (P/N 222-382-001-107). Since the same type of servo actuator was also used on other Bell Helicopter Textron helicopters, additional alert service bulletins were issued: ASB 230-10-41 for specific Bell Model 230 helicopters, ASB 222U-10-80 for specific Bell Model 222U helicopters, and ASB 222-10-109 for specific Bell 222 and 222B helicopters.
Regulatory Response
The Federal Aviation Administration (FAA) incorporated the recommended actions from these service bulletins, with some minor revisions, into Emergency Airworthiness Directive AD-2010-19-51, effective September 1, 2010. This FAA emergency AD followed the issuance of an Airworthiness Directive by Transport Canada, CF-2010-29, dated August 26, 2010.