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Service Difficulty Advisory

AV 2009-01
April 17, 2009

PT6A Engines: Handling of External Engine Tubes and Fittings

Transport Canada Civil Aviation (TCCA) has received several reports of fuel by-pass tube, Part No. (P/N) 3011849 cracking at the start control unit fittings. In some instances, fuel leaking from the cracked tube was ingested into the engine compressor and into the cabin. One of the main reasons for the failure is the mishandling of tubes during maintenance activity. 

Pratt & Whitney (P&WC) Service Information Letter (SIL) No. Gen. PT6A-026 dated 29 May 2008 states: “Operators, maintenance providers and Repair and Overhauled facilities are reminded to adhere to Engine Maintenance Manual procedures during engine accessory or Power Section removal and installation. When aligning hydraulic or pneumatic tubes (whether rigid or flexible) with mating fittings, exercise caution to avoid bending, twisting, or forcing the components. Rigid tubes in particular should be loosened or disconnected at both ends to prevent distortion or the application of excessive stresses at the tubes ends. Ensure proper alignment of external  oil tubes prior to axial engagement with alloy fittings.

TCCA recommends Operators, Aircraft Maintenance Engineers, and Repair and Overhaul facilities exercise caution while performing repairs and/or replacing components.  Refer to P&WC SIL No. Gen. PT6A-026 and P&WC Maintenance Manual Chapter 70, Standard Practices.

Schematic on how to assemble a Fuel Control Unit

Click on image above to enlarge

Defects, malfunctions, and failures occurring on aeronautical products should be reported to Transport Canada, Continuing Airworthiness in accordance with CAR 591 mandatory Service Difficulty Reporting requirements.

For further information, contact a Transport Canada Center, or Mr. Guy Richard, Continuing Airworthiness, Ottawa at 613-941-7466, facsimile 613-996-9178, or email guy.richard@tc.gc.ca

or Director, National Aircraft Certification

Derek Ferguson
Acting Chief, Continuing Airworthiness

Note:    For the electronic version of this document, please consult the following Web address:

www.tc.gc.ca/eng/civilaviation/certification/menu.htm