AD/DHC-8/125 Main Landing Gear Shock Strut Piston (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-8/125 Main Landing Gear Shock Strut Piston 8/2006

Applicability:

Bombardier Inc. DHC-8 Models 101, 102, 103, 106, 201, 202, 301, 311, 314 and 315, serial numbers 003 through 618.

Requirement:

1.    Applicable to Bombardier DHC-8 Models 311, 314 and 315, serial numbers 202 through 516, with main landing gear (MLG) shock struts in the serial number range DCL3501/90 to DCL3768/97 installed.  Also all spare main landing gear shock struts in the same serial number range.

Remove the anti-rotation needle roller from the upper bearing of the main landing gear shock strut by incorporating Modsum 8/3331 in accordance with Bombardier Service Bulletin 8-32-144 Revision A, dated 29 April 2002, or later Transport Canada approved revisions.

Note 1:  Previous incorporation of Modsum 8/3331, in accordance with the Accomplishment Instructions in the original issue of Bombardier Service Bulletin
8-32-144, dated 10 August 1998, meets the requirements of this part.

2.    Applicable to DHC-8 Models 101,102,103,106,201,202, 301, 311, 314 and 315 serial numbers 003 to 614.

Amend the Transport Canada approved maintenance schedule by incorporating MLG Shock Strut Servicing task 3210/15 into Part 1 of the DHC-8 Maintenance Program Manual as specified below:

A/C Series	PSM No.	Rev No.	Task No.
100	1-8-7	20	3210/15
200	1-82-7	11	3210/15
300	1-83-7	20	3210/15

3.    Applicable to DHC-8 Models 101,102,103,106,201,202, 301, 311, 314 and 315 serial numbers 003 to 618.

The following parts shall not be used as replacements during the repair or overhaul of any shock strut assembly:

Part	Number
Upper Bearing	P/N 10130-3, 10130-551
Damper Ring	P/N 10129-3, 10129-551

Instead, the following parts are to be used:

Part	Number
Upper Bearing	P/N 10130-5
Damper Ring	P/N 10129-5, 10129-553

In addition, for any MLG with a reworked oversize cylinder bore (part number identified as per the Component Maintenance Manual (CMM), the following parts are to be used in accordance with the applicable CMM:

Part	Number
Upper Bearing	P/N CRS85-167-11
Damper Ring	P/N CRS85-167-31, CRS85-167-33
Seal Carrier	P/N CRS85-167-21

Note 2:  Transport Canada AD CF-2006-14 dated14 June 2006 refers.

Compliance:

1.    Within 3000 flight hours after the effective date of this directive, unless already accomplished.

2.    Within 30 days after the effective date of this directive, unless already accomplished.

3.    As of the effective date of this AD.

This Airworthiness Directive becomes effective on 3 August 2006.

Background:

Over the past 10 years there have been six cases reported in which the MLG shock strut piston has over-extended, allowing the torque links to go over-centre and rest on the piston.  This resulted in a loss of shock absorption on touchdown and, in one case, also resulted in failure of the shock strut cylinder housing.  Although it has not occurred in any of the reported cases, failure of the shock strut cylinder housing could also possibly result in a subsequent loss of directional control.

Investigation has determined that over-extension of the shock strut resulted from damage to the upper bearing and seal carrier, caused by a loss of internal damping.

James Coyne
Delegate of the Civil Aviation Safety Authority

21 June 2006