6 April 2005
During cruise flight, the crew was alerted to a right engine low oil pressure warning light on the annunciator panel. A visual scan of the engine gauges revealed that the oil pressure was at 40 psi and decreasing. A precautionary engine shutdown was carried out to avoid engine oil starvation. The aircraft continued to its nearby place of destination on the remaining left engine.
Maintenance personnel determined the cause of engine low oil pressure to be a crack at the mounting flange of the oil filter adaptor. The crack then propagated to the oil filter adaptor "O" ring groove and exhausted three of the eight quarts of engine oil to atmosphere.
The oil filter adaptor is located in a very confined area and is thus difficult to align during installation. During installation, the adaptor is drawn into the gear case by evenly turning down the flange-mounted nuts, until such time as the adaptor has mated to the gear case. It is suspected that this difficulty of installation (possible misalignment causing resultant stresses) may lead to crack(s) on the adaptor. During adaptor removal, it is also suspected that personnel may be incorrectly using a leverage tool to pry on the adaptor flange. Additionally, poor installation and removal practices for the oil filter bowl may also contribute to adaptor cracks.
A major Canadian operator and engine approved maintenance organization (AMO) have reported several incidents of cracked oil filter adaptors via the SDR system. A precautionary inspection of their own aircraft fleet revealed two other cases of cracked adaptors. The operator has now commenced the use of non-destructive testing techniques to detect cracks to prevent further failures. The operator is phasing out the older style oil filter adaptors and oil filter caps, which will further reduce occurrences.
Garrett Turbine Engine Company has developed a new oil filter adaptor, part number 896700-2, with a built-in swivel that provides easier installation. Please refer to FAA-approved Service Bulletin (SB) TPE331-79-0012 to determine the applicability of TPE 331 series engines. Also, Honeywell (Garrett) Service Bulletin TPE331-79-0010 introduces a newer style oil filter and cap assembly that utilizes a wrench to assist installation.
Transport Canada recommends that owners, operators and other responsible persons comply with the above-mentioned manufacturer's Service Bulletins.
Any further defects or occurrences should be reported to Transport Canada, Continuing Airworthiness, Ottawa, via the Service Difficulty Reporting program.
For further information contact a Transport Canada Centre, or contact Mr. Barry Caldwell, Continuing Airworthiness, Ottawa, telephone 613 952-4358 , facsimile 613 996-9178 or e-mail firstname.lastname@example.org
For Director, Aircraft Certification
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