PW901A and PW901C auxiliary power unit fires - Civil Aviation Safety Alert (CASA) No. 2020-09


Owners, operators and maintainers of Pratt & Whitney Canada PW901A and PW901C auxiliary power units

File Classification No.: Z 5000-35
RDIMS No.: 14886711
Document No.: CASA 2020-09
Issue No.: 01
Effective Date: 2020-09-15


The purpose of this Civil Aviation Safety Alert (CASA) is to raise awareness of starter issues associated with the servicing of PW901A and PW901C auxiliary power unit (APU) starters to reduce the risk of APU fires.


Transport Canada has been made aware of events where the starter clutch mechanism has re-engaged or the clutch failed to disengage after APU start-up. This condition has led to APU fires. Review of the components and of the starter motor maintenance practices uncovered potential discrepancies that may compromise the oil system and affect the durability of the unit. Investigation indicates that some overheating of components was present and this condition may signify insufficient lubrication of the clutch components. In light of these discrepancies and of the investigation findings, Pratt & Whitney Canada in conjunction with starter manufacturer Labinal Power (Safran) and the aircraft manufacturer Boeing, have implemented improvements to Instructions for Continued Airworthiness (ICA).

Recommended action:

Transport Canada recommends that operators and maintainers familiarize themselves with the instructions contained in Pratt & Whitney Canada Service Information Letter PW900-24R1 (available at Pratt & Whitney’s Website: and maintain these units in accordance with the latest Instructions for Continued Airworthiness (ICA).

Contact office:

For more information concerning this issue, contact a Transport Canada Centre; or contact Cliff Lefrense, Continuing Airworthiness in Ottawa, by telephone at 1-888-663-3639, facsimile at 613-996-9178 or e-mail at

Original signed by

Rémy Knoerr
Chief, Continuing Airworthiness
National Aircraft Certification

The Transport Canada Civil Aviation Safety Alert (CASA) is used to convey important safety information and contains recommended action items. The CASA strives to assist the aviation industry's efforts to provide a service with the highest possible degree of safety. The information contained herein is often critical and must be conveyed to the appropriate office in a timely manner. The CASA may be changed or amended should new information become available.