BELL 430 near Venice, LA — 2010-08-04

Probable cause

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

NTSB narrative

On August 4, 2010, at 0645 central daylight time, a Bell Helicopter Textron 430 was on the ground at ground idle power conducting the engine start checklist when the collective went to the full up position. 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 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. In response to this incident, Bell Helicopter Textron issued a number of alert service bulletins to perform a one time inspection of the servo actuator piston rod prior to further flight. This service bulletin only applied to servo actuators manufactured by Woodward HRT. Since this same type of servo actuator was also used on other Bell Helicopter Textron helicopters, additional alert service bulletins were issued. The Federal Aviation Administration (FAA) incorporated these service bulletins’ recommended actions (with some minor revisions) in an Emergency Airworthiness Directive. The FAA’s emergency AD followed the issuance of an AD by Transport Canada.

Analysis

Primary failure mode

Mechanical failure

First missed decision gate

Inspection of the servo actuator piston rod prior to flight could have prevented failure.

NTSB coding

• Flight control sys malf/fail · Prior to flight

Evidence available

• 1 docket document

Docket documents1

• Airworthiness Factual Report of Group Chairmanreport