Ad/DHC-8/150 - Nose Landing Gear Pivot Retention Bolt (Cth)

AIRWORTHINESS DIRECTIVE

For the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.001(1) of CASR 1998.  The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.

Bombardier (Boeing Canada/De Havilland) DHC-8 Series Aeroplanes

AD/DHC-8/150 Nose Landing Gear Pivot Retention Bolt 10/2009

Applicability:

Bombardier Inc. DHC-8 Aircraft, Models 400, 401 and 402, Serial Numbers 4001, 4003, 4004, 4006 and 4008 through 4238.

Requirement:

Incorporate Bombardier Modsum 4-113599.

Bombardier Service Bulletin 84-32-65, initial Issue, dated 17 December 2008, or Revision A, dated 2 March 2009 or later revisions approved by the Chief, Continuing Airworthiness, Transport Canada provides approved instructions for incorporating Modsum 4-113599.

Note:  Transport Canada AD CF-2009-29 dated 20 July 2009 refers.

Compliance:

Within 2,000 flight hours after the effective date of this AD, unless previously accomplished.

This Airworthiness Directive becomes effective on 24 September 2009.

Background:

Two in-service incidents have been reported on DHC-8 Series 400 aircraft 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 tyre 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 tyre.  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 tyre or the loss of directional control could adversely affect the aircraft during take off or landing.

To prevent the potential failure of the pivot pin retention bolt, Bombardier Aerospace has developed a modification which includes 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.

James Coyne
Delegate of the Civil Aviation Safety Authority

14 August 2009