Pratt & Whitney Canada engines oil filler cap security - Service Difficulty Advisory

No. AV-2006-08
22 September 2006

Transport Canada Civil Aviation (TCCA) and Pratt & Whitney Canada (P&WC) have received numerous reports of service difficulties involving improperly secured engine oil filler caps. In some cases, the oil cap has inadvertently been left off.

Loose, leaking or missing filler caps may lead to loss of engine oil in subsequent operation resulting in low engine oil pressure and in-flight shutdowns (IFSD). Operation at oil pressures lower than that prescribed in the engine operating limitations section may cause significant bearing damage and costly maintenance and repairs.

Recently, a low oil pressure warning on a PW200 engine forced the pilot to carry out an IFSD and unplanned landing. It was later discovered that the oil cap been left off.

Another low oil pressure event on a PT6A-powered King Air (A90) resulted in an IFSD and one engine inoperative (OEI) landing. Ground investigation revealed that the oil cap had been improperly secured.

A low engine low oil pressure incident occurred on a PW120A engine during climb, requiring an IFSD and single engine landing. Again, post-flight inspection revealed that the oil cap had been left off.

Similar events have also been reported to occur on PW300 series engines turbofan engines.

P&WC has developed and introduced oil filler check valves on the majority of models to reduce oil loss under the above conditions. While this feature is basic to the design of newer engine models, it has also been incorporated in legacy product lines through the following Service Bulletins:

T6A Series PT6T Series PW100 Series PW200 Series PW300 Series
SB 1451 SB 5459 SB 21150 SB 28221 SB 25219
SB 1506   SB 21700   SB 24539
SB 3378        
SB 13340        
SB 14301        

P&WC has also recently published Service Information Letter (SIL) PW100-107 advising operators of PW100 series engines of inspection criteria for oil filler check valves.                  

A recent service difficulty involving oil loss on a PT6A-114A engine alerted P&WC to a manufacturing quality issue affecting a limited number oil filler caps on PT6A, PW100 and PW500 series engines. This involved a lower than specified run-down torque on the filler cap assembly lock-nut which could potentially result in the loss of cap sealing function over a period of operation. P&WC has issued service bulletins SB1637, SB21720 and SB30294, respectively, requesting operators to perform inspections of the oil filler cap and to repair or replace as necessary.

Transport Canada Civil Aviation (TCCA) recommends that all operators, maintainers, overhaul facilities and other interested parties comply with the aforementioned P&WC Service Information Letter and Service Bulletins. Following engine oil servicing, always double check to ensure that oil caps are properly fastened.

Any further defects or occurrences should be reported to Transport Canada, Continuing Airworthiness, Ottawa, via the Service Difficulty Reporting System.

For further information, please contact a Transport Canada Centre, or contact Mr. Barry Caldwell, Continuing Airworthiness, Ottawa, telephone 613-952-4358, fax 613-996-9178, or e-mail

For Director, Aircraft Certification

B. Goyaniuk
Chief, Continuing Airworthiness

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