AD/DHC-8/114 Pitch Trim Control (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-8/114 Pitch Trim Control 4/2006

Applicability:	DHC-8 Models 400, 401 and 402 aeroplanes, serial numbers (S/N) 4001 through 4065.
Requirement:	1.    For aeroplanes S/N 4001 through 4058 - If not previously accomplished, incorporate Modsum 4-113405 by replacing/reworking FGM1 and FGM 2 P/N C12429AA06 with/to FGM P/N C12429AA07 and perform a Return to Service Procedure.  Bombardier Service Bulletin (SB) 84-22-04 Auto Pilot - Flight Guidance Module (FGM) - Introduction of Software V666 - Modsum 4-113405 dated 29 November 2001, or later revisions, approved by the Chief, Continuing Airworthiness, Transport Canada provides approved instructions for incorporating Modsum 4-113405.
Note 1:  As an interim procedure, until such time as Modsum 4-113405 is implemented, the procedure detailed in Bombardier Service Letter (SL) DH8-400-SL-22-001D dated 8 November 2001 can be used as an approved maintenance procedure to confirm that the AP pitch trim function is serviceable and to restore use of the auto pilot following an autopilot pitch trim failure.  This autopilot pitch trim failure is characterized by an “AP PITCH TRIM FAIL” message on the PFD, followed by an “AUTO TRIM FAIL” message after the AP has been manually disengaged.
2.    For aeroplanes S/N 4001 through 4065 - If not previously accomplished, incorporate Modsum 4-113392 by removing Flight Control Electronic Control Units (FCECU) that have either Part Number (P/N) 398500-1001 or P/N 398500-1003 and replacing with FCECU P/N 398500-1005.  Bombardier (SB) 84-27-14 Flight Controls - Flight Control Electronic Control Unit Upgrade - Modsum 4-113392 dated 16 January 2002, or later revisions approved by the Chief, Continuing Airworthiness, Transport Canada, provides approved instructions for replacing the affected FCECUs.
Note 2:  As an interim procedure, until such time as Modsum 4-113392 is incorporated, the procedure detailed in Bombardier SL DH8-400-SL-27-003 dated 22 May 2001 can be used as an approved maintenance procedure to confirm that the pitch trim system is serviceable following loss of manual pitch trim.  This pitch trim failure is characterized by illumination of the “PITCH TRIM” Caution Light and concurrent loss of pitch trim function, during a manual pitch trim input by the flight crew.

Note 3:  Transport Canada AD CF-2002-25 refers.
Compliance:	For Requirements 1 and 2 - Within 30 days after the effective date of this Directive.
This Airworthiness Directive becomes effective on 13 April 2006.
Background:	Transport Canada has advised that two unrelated but recurring malfunctions have been identified with the pitch trim system.  The first malfunction involves loss of the autopilot pitch trim, which then requires that the autopilot be disengaged and the aircraft flown manually.  With the second malfunction, loss of manual pitch trim can occur due to the pitch trim system being disabled by the monitoring/modelling circuitry in the FCECU.  These pitch trim system malfunctions can, under adverse conditions, significantly increase flight crew workload.

James Coyne
Delegate of the Civil Aviation Safety Authority

2 March 2006