Transport Canada

Nose Landing Gear - Loss Of Pivot Pin Retention Bolt
 N AD CF-2009-29R2

Annotation

Background:

Two in-service incidents have been reported on DHC-8 Series 400 aeroplanes in which the nose landing gear (NLG) trailing arm pivot pin retention bolt (part number NAS6204-13D) was damaged. One incident involved the left hand NLG tire which ruptured on take-off. Investigation determined that the retention bolt failure was due to repeated contact of the castellated nut with the towing device including both the towbar and the towbarless rigs. The loss of the retention bolt allowed the pivot pin to migrate from its normal position and resulted in contact with and rupture of the tire. The loss of the pivot pin could compromise retention of the trailing arm and could result in a loss of directional control due to loss of nose wheel steering. The loss of an NLG tire or the loss of directional control could adversely affect the aeroplane during take off or landing.

To prevent the potential failure of the pivot pin retention bolt, Bombardier Aerospace developed a modification which included a new retention bolt, a reverse orientation of the retention bolt and a rework of the weight on wheel (WOW) proximity sensor cover to provide clearance for the re-oriented retention bolt.

Since the original issue of this AD, there have been several reports of pivot pin retention bolts found missing or damaged. Additional investigation determined that the failures were caused by high contact stresses on the retention bolt due to excessive frictional torque on the pivot pin and an adverse tolerance condition at the retention bolt.

Revision 1 of this AD mandated the installation of a new pivot pin retention mechanism.

Since the issue of Revision 1 of this AD, there have been reports of chrome peeling on special bolt part number 47205-1 at the pivot pin link resulting in corrosion of the bolt substrate layer.