NTSB Factual Report

On August 4, 2010, at 0645 central daylight time, a Bell Helicopter Textron 430 (registration N430CM), was on the ground at ground idle power conducting the engine start checklist when the collective went to the full up position. The pilot was unable to lower the collective, the helicopter's engines were shut down, and the pilot and seven passengers disembarked normally. The flight, operated under the provisions of Title 14 CFR Part 91, was intending to fly to an oil rig platform off the coast of Louisiana. There were no injuries among the passengers and crew. 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 the Bell Helicopter Textron's Field Investigations Laboratory. According to Bell Helicopter Textron, 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. Their 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.

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. This service bulletin advised 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 only applied to servo actuators manufactured by Woodward HRT (P/N 222-382-001-107). Since this same type of servo actuator was also used on other Bell Helicopter Textron helicopters, additional alert service bulletins were issued. Alert service bulletin (ASB) 230-10-41 applied to specific Bell Model 230 helicopters, ASB 222U-10-80 applied to specific Bell Model 222U helicopters, and ASB 222-10-109 applied to specific Bell 222 and 222B helicopters.

The Federal Aviation Administration (FAA) incorporated these service bulletins' recommended actions (with some minor revisions) in Emergency Airworthiness Directive AD-2010-19-51, effective September 1, 2010. The FAA's emergency AD followed the issuance of an AD by Transport Canada, CF-2010-29, dated August 26, 2010.

NTSB Probable Cause

The fracture of the collective servo actuator piston rod resulting from stress corrosion cracking.