Document ID: chunk:federal_register_of_legislation:F2008L04173:body:0:p2
Version: federal_register_of_legislation:F2008L04173
Segment Type: other
Provision Reference: 
Character Range: 2855–4348

reports that two Model MD900 helicopters experienced broken Vertical Stabilizer Control System (VSCS) adapter tubes.  In one case, the helicopter experienced uncommanded yaw, resulting in loss of a window and a door.  The same part-numbered adapter tube is used on the Model 500N and 600N helicopters Yaw Stability Augmentation System (YSAS).  Some of the VSCS and YSAS adapter tubes were not manufactured to the required specifications and can fail.  This condition, if not corrected, could result in loss of yaw control and subsequent loss of control of the helicopter.

             Amendment 1 was raised in response to the FAA being advised that the action of pulling the CB can result in impaired directional control which could result in loss of control of the helicopter.  Therefore amendment 1 required that the YSAS is turned off instead of pulling the CB.

             Amendment 2 removes reference to any serial numbers in the applicability section because the unsafe condition can occur on any helicopter with the affected tubes installed.  This amendment also requires that replacement adaptor tubes have a production date code stamped on them to determine that the parts are airworthy. (e.g., 08-08 indicates a production date of August 2008).

             The original issue of this AD became effective on 26 August 2008.

             Amendment 1 of this AD became effective 28 August 2008.

James Coyne
Delegate of the Civil Aviation Safety Authority

24 October 2008