All Model DHC-3 aeroplanes powered by radial engines incorporating a firewall magneto connector plug as described in Viking Air Limited Service Bulletin (SB) V3/0001.
Requirement:
1. If not previously accomplished in accordance with the original issue of this Directive, perform a visual inspection of the firewall ignition plug and receptacle for proper lock wiring and security in accordance with the Accomplishment Instructions of Bombardier Aerospace de Havilland Otter Alert Service Bulletin A3/53, Revision ‘A’ dated 30 August 2001 or later revision approved by the Chief, Continuing Airworthiness, Transport Canada.
2. Replace any damaged parts detected during the Requirement 1 inspection.
3. If not previously accomplished in accordance with the original issue of this Directive, incorporate Maintenance Manual PSM 1-3-2 Temporary Revision TR14, dated 24 August 2001, into the periodic inspection of the aircraft approved maintenance schedule. Once incorporated, this inspection is considered a routine task subject to normal maintenance program development and escalation.
TR14 may be removed from the Maintenance Manual when it is superseded by a normal revision to the manual.
4. Replace the firewall magneto connector in accordance with the accomplishment instructions of Viking Air Limited SB V3/0001 dated 27 June 2007, or later revisions approved by the Chief, Continuing Airworthiness, Transport Canada.
Note: Transport Canada AD CF-2001-37R1 refers.
Compliance:
For Requirement 1 - Within 3 months or 110 hours time in service after the effective date of this Directive, whichever occurs first.
For Requirement 2 - Before further flight after the Requirement 1 inspection.
For Requirement 3 - Within 3 months after the effective date of this Directive.
For Requirement 4 - Before 1 August 2008.
This Amendment becomes effective on 10 April 2008.
Background:
Transport Canada has advised that a complete loss of both ignition systems occurred on a DHC-3 Otter when the lock wire hole in the ignition connector plug on the firewall broke out, allowing the plug to vibrate loose. A maintenance safety feature grounds out both magneto systems through a spring-loaded safety pin incorporated into the Cannon plug.
The original issue of this Directive required a one time inspection of the ignition connector plug to detect any discrepancies and, if necessary, their rectification. The Directive also required amendment of the Maintenance Manual.
Subsequent to the issuance of AD CF-2001-37 (AD/DHC-3/37) a complete loss of both ignition systems occurred on a DHC-2 Beaver, resulting in engine failure and subsequent forced approach and landing. Investigation by the Canadian Transportation Safety Board determined the internal failure of the magneto firewall connector resulted in both magneto “P” leads shorting to ground. A maintenance “safety” feature through a spring-loaded safety pin incorporated in the firewall connector on many DHC-2 aircraft grounds out both magneto systems when the connector is disconnected. This connector type is readily identified, when disconnected by the existence of three internal pins on the firewall and magneto harness side, one of which is shorted directly to ground.These connectors have also been installed on the DHC-3 aircraft but are no longer in production.Since no effective Instructions for Continued Airworthiness exist to ensure the safety feature of these connectors will operate correctly when disconnected, or will ensure the internal integrity of the connector while in service, this Directive is revised to mandate replacement of connectors with a different design.Viking Air Limited has developed SB V3/0001 to provide for the installation of a replacement connector, similar in design to magneto systems in service today. This modification incorporates a “straight through” type connector, ensuring magneto circuit integrity should the connection open.
The original issue of this Directive became effective on 29 November 2001.
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David Punshon
Delegate of the Civil Aviation Safety Authority