Lease Transition – APU Condition / Implication Considerations

The Auxiliary Power Unit (APU) of an aircraft regarding lease transition conditions functions similarly to an engine and the APU also has its independent monitoring system. The APU’s operational hours and start-ups (cycles) are tracked distinctly, unrelated to the aircraft’s hours or cycles.

Typically, the hours are lower than the cycles for an APU as it is started when ready for flight or on engine shutdown and not commonly run for long periods of time.

Also on the APU are various individual components such a generator or starter, the APU might also include Life Limited Parts (LLPs). Its performance is consistently monitored through indicators such as oil consumption, Exhaust Gas Temperatures (EGT), and internal inspections using a specialized camera inspection known as a borescope. Depending on these evaluations, the APU might need maintenance off the aircraft, commonly termed a “shop visit.”

The review process of the APU shares several parallels with that of engines, both have detailed status reports, including compliance with Airworthiness Directives (ADs) and Service Bulletins (SBs). Moreover, the APU maintains a historical record, and its removal and replacement on an aircraft is straightforward resulting in very little ground time providing a spare is available – it is also possible to fly the aircraft with the APU inoperative for a short time – this might be a consideration an aircraft paint input during a lease transition.

From the APU trend monitoring there are particular indicators, such as elevated oil consumption or EGT that can hint at potential APU issues.

Leasing periods often see the APU in active use, primarily when it’s the sole power source in a location that the aircraft is in such as remote airfields. It’s essential to cross-check the hours and cycles on the statement with the aircraft acceptance document post ferry or demo flights, as mandated by the lease agreement. Depending on various factors, such as the lease term or operational conditions, an APU could undergo multiple shop visits during its lifecycle.

Lastly, minor shop visits are possible for APUs, with reasons and the time and cycles since the last shop visit (TSLSV/CSLSV) being crucial. This information, along with hours and cycles, will typically be provided by the lessee in a comprehensive statement.

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