AD/DHC-8/148 Elevator Power Control Unit (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-8/148 Elevator Power Control Unit 7/2009

Applicability:

Bombardier Inc. DHC-8 Models 400, 401 and 402, Serial Numbers (S/N) 4135 through 4149.

Requirement:

1.    Inspect the serial number of each of the six installed elevator Power Control Units (PCU)s, Part Number (P/N) 390600-1007.

a.     Compliance with this AD is complete, and no further action is required, if all six of the installed PCUs have suffix “A” after the serial number and/or have a serial number that is not in the following range:

PCU S/Ns 238, 698, 783 through 788, 790, 793, 795, 802, 806, 807, 810, 820 through 823, 826 through 828, 831, 835, 838, 840, 886 through 889 or 898 through 955.

b.    If one or more of the installed PCUs has a serial number in the above range without a suffix “A”, proceed to Requirement 2 of this AD.

Note 1:  Suffix “A” after the S/N indicates that the PCU has already passed a magnetic particle inspection and is cleared for continued use.

2.    Perform a daily check for the correct operation of all installed elevator PCUs.

Note 2:  Requirement 2 of this AD is only applicable if required by Requirement 1.b.) of this AD.

Note 3:  Requirement 2 of this AD is no longer required following accomplishment of Requirement 3 of this AD.

Note 4:  Requirement 2 of this AD can be achieved by accomplishment of the procedures detailed in Appendix A, B or C of Bombardier Q400 All Operator Message No. 217B, dated 26 April 2007.

3.    a.     Remove all elevator PCUs that have S/Ns listed in Requirement 1.a.) of this AD and do not have suffix “A” after the S/N.

b.    Replace each removed PCU with a PCU, P/N 390600-1007, which has a S/N outside the range listed in Requirement 1a) of this AD or has suffix “A” after the S/N.

Note 5:  Bombardier Service Bulletin (SB) 84-27-32, Revision A, dated 18 January 2008, or later revisions approved by the Chief, Continuing Airworthiness, Transport Canada, provides approved instructions for the removal and replacement of the PCUs and for subsequent rigging of the elevators.

Note 6:  Previous accomplishment of Bombardier SB 84-27-32, original issue, dated 1 May 2007, meets Requirement 3 of this AD.

Note 7:  Transport Canada AD CF-2009-16 dated 20 April 2009 refers.

Compliance:

For Requirement 1 - Within 30 days after the effective date of this AD.

For Requirement 2 - Commencing no later than 30 days after the effective date of this AD.

For Requirement 3 - Within 2000 flight hours or within 12 months after the effective date of this AD, whichever comes first, unless already accomplished.

This Airworthiness Directive becomes effective on 2 July 2009.

Background:

There has been one case reported of failure of a shaft (tailstock) on an elevator PCU, P/N 390600-1007.  Continued actuation of the affected PCU caused damage to the surrounding structure.  Subsequent investigation determined that the failure was the result of a material defect and that the shafts installed on a total of 88 suspect PCUs.

Each elevator surface has three PCUs, powered by separate independent hydraulic systems, and a single elevator PCU shaft failure may remain dormant.  Such a dormant loss of redundancy, coupled with the potential for a failed shaft to produce collateral damage, including damage to hydraulic lines, could possibly affect the controllability of the aircraft.

This AD mandates an identification check for elevator PCU serial numbers, a daily check for correct operation of all suspect PCUs and, finally, replacement of all suspect PCUs.

James Coyne
Delegate of the Civil Aviation Safety Authority

22 May 2009