AD/DHC-8/144 De-Ice Busbar Sealant (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-8/144 De-Ice Busbar Sealant 3/2009

Applicability:

DHC-8 Models 400, 401 and 402, Serial Numbers 4001, 4003, 4004, 4006 and 4008 through 4154.

Requirement:

1.    Amend the aircraft Flight Manual (AFM), PSM 1-84-1A, by inserting Temporary Amendment (TA) No 14, dated 10 May 2006, or later approved changes to this TA.

2.    Apply sealant between the bus bar assemblies and the backplate assembly by incorporating Modsum 4-163047.  Bombardier Service Bulletin (SB) 84-61-03, Revision A, dated 18 September 2007, or later revisions approved by Chief, Continuing Airworthiness, Transport Canada, provides approved instructions for incorporating Modsum 4-163047.

Note 1:  Incorporation of Modsum 4-163047 in accordance with the original issue of SB 84-61-03, dated 27 April 2007, also meets the intent of this Directive.

Note 2:  Transport Canada AD CF-2009-01 refers.

Compliance:

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

For Requirement 2 - Within 5 000 hours time in service after the effective date of this Directive.

This Airworthiness Directive becomes effective on 12 March 2009.

Background:

Four aircraft have experienced a dual AC generator shutdown, caused by a broken propeller de-ice bus bar which short-circuited with the backplate assembly.

Investigations subsequently determined that any friction or contact between a propeller de-ice bus bar and the backplate assembly can cause an intermittent short circuit.  Such a short circuit can cause a dual AC generator shutdown that, particularly in conjunction with an engine failure in icing conditions, could result in reduced controllability of the aircraft.

This Directive mandates revision of the AFM to introduce a procedure that restores AC power following failure of No.1 and No.2 AC generators with propeller de-ice on.  Additionally, in order to prevent similar dual AC generator shutdowns, it mandates the application of sealant as insulation between the propeller de-ice bus bars and the backplate assembly.

James Coyne
Delegate of the Civil Aviation Safety Authority

27 January 2009