APU’s are qualified by Honeywell to a Federal Aviation Administration (FAA) document called a Technical Standard Order (TSO), specifically TSO-C77A. This means that a series of bench and engine tests are used to prove to the FAA that our APUs meet certain safety and performance standards. Once Honeywell receives the TSO qualification from the FAA the APU is then installed into the aircraft by an aircraft manufacturer where it is certified to FAA Part 25 requirements. This distinction is very important because it determines who is responsible for field documentation. Because Honeywell does not own the Type Certificate (similar to that used for most main engines) for the APU installation we cannot legally provide on-wing inspection or repair dispositions, this is all controlled and provided by the aircraft manufacturer.
Operators requiring specific APU inspection and or repair criteria should contact the aircraft manufacturer for disposition. Honeywell will work in concert with the aircraft manufacturer to provide technical support and recommendations as requested but all documentation to the aircraft owner/operator will be provided by the aircraft manufacturer.