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PW305: Less Than Expected Service Life from APC Starter Generators

January 2014

Duncan Aviation technicians have found that the APC starter generator P/N 400SG138Q-() currently found on some P&W305 engines isn't performing as expected and falling short of projected TBO, creating some reliability uncertainty. This is caused by the high levels of heat generated during initial start-up of the PW305 engine on certain model aircraft. If the amperage is not allowed to drop before the second engine is started, the demand on the starter generator remains high and the continued higher heat may cause early failure of the APC starter generator, requiring its early removal and overhaul.

To reduce premature removal of the APC starter generator, I recommend you consider replacing the APC unit with the Safran Power UK & Safran Power USA starter generator, P/N 23091-009. It has received full STC and PMA certification, as well as EASA approved. And is a direct replacement that requires no aircraft modification.

Longer Brush Life

The Safran starter generator is specifically designed for the PW305 engine on certain model aircraft and is fitted with proprietary brushes (P/N 23080-1983) that are non-impregnated and have a slanted core type design. There are some technical advances of the Safran slanted core brush over the straight core brushes that have been used for many years.

The Base Carbon

The base carbon - the mechanical properties of the base carbon in the slanted core brushes have been enhanced slightly through minor changes in the processing without affecting its commutating properties. This provides an improvement in brush life at full rated load over a broader speed range. However, because the basic materials of the brush have not changed, the basic characteristics of the brush such as RFI and voltage drop have also not changed.

Extended Commutator Life

The Patented slanted core design of the brush helps reduce the commutator wear and prevents 'grooving,' which in turn maximizes commutator life.


A non-impregnated brush has a lower brush drop resulting in a lower brush temperature and a lower minimum speed for regulation for the starter generator.

Safran Power UK & Safran Power USA has an excellent track record regarding reliability and maintenance resulting in reduced maintenance, aircraft downtime and operating costs. Duncan Aviation is a distributor of the Safran Power UK & Safran Power USA Starter Generator worldwide. For more information, download this Safran Power UK & Safran Power USA Starter Generator information sheet or please call 800.228.1836,  +1 402-475-4125.