The Do's and Don'ts of Auxiliary Power Unit Preventive Maintenance

Tucked away in the tail cone of aircraft, APUs are truly the unseen work horses of the commercial aviation industry. These four best-practice tips will help ensure your APU functions smoothly.

“The APU is an important component of commercial airliners. To ensure the reliability of your aircraft, you need to maintain the APU in the same way as you would your powerplant engine,” as P&WC’s Chris Yip, PW900 Customer Engineering, explains to Airtime.

There are over 4,000 P&WC-manufactured APUs in service around the world. They include the PW901A (Boeing 747-400), PW901C (Boeing 747-8), PW980 (Airbus A380), APS3200 (Airbus A320ceo and A320neo families), APS2300 (Embraer E-Jets), APS2600 (Embraer E-Jets E2, Mitsubishi Regional Jet and COMAC ARJ21) and APS5000 (Boeing 787 Dreamliner).

Do: Take Good Care of Your Connector

Intermittent or lost electric signals can lead to AutoShutdown and/or difficulty in Starting. The high location of the APU in the tail section of the aircraft can turn troubleshooting of this fault into a challenging task.

Fortunately, P&WC has developed a “connector care” procedure that has been shown to reduce the incidence of faulty signals. This four-step process involves cleaning the connectors, improving the conductivity, torqueing it with the designated tooling (for example, soft-jaw pliers) and, finally, taping it. Chris recommends doing this every time a connector is removed, as it will help prevent unnecessary maintenance interventions and parts replacement.

"Connector care is a best practice that will cost you nothing extra over the life of the engine. It's been proven in the field on P&WC turboprop engines. "

- CHRIS YIP, PW900 CUSTOMER ENGINEERING

Don't Put Off Replacing Parts

If you identify a minor issue such as a damaged sensor connection or fuel manifold, don't wait to do something about it. These seemingly small issues could have a major impact, like reducing the hot section life or impeding the starting fuel flow.

Along with the use of predictive and preventive maintenance tools, Chris recommends taking advantage of a scheduled shop visit to handle any other maintenance needs at the same time, including replacing APU parts approaching the end of their cycle. It’s vital to replace mechanical parts—such as starters or fuel pumps—that are nearing the end of their life in a timely fashion. Wait too long and they’ll start to break down, leading to unplanned shop visits for repair or replacement and potential dispatch issues.

Chris compares it to best practices for car engine maintenance: “If you know the life of your car’s battery is eight years, you don’t wait until it fails then call for roadside assistance when you’re stuck on the highway. You replace it before it breaks. It’s exactly the same for an APU,” he remarks.

Do: Conduct Regular Monitoring and Inspections

As recommended in the component maintenance manual, always do continuous on-condition monitoring of APU parameters. This will allow you to spot any unusual variations in performance and address them promptly, which can significantly reduce costs and maintenance workload in the long run.

Check for issues that could impact performance like abnormal hardware conditions, the presence of debris or oil leaks. If you spot anything, take the necessary maintenance actions.

Operators of PW980 and APS5000 models can also leverage P&WC's innovative Oil Analysis Technology, an on-wing engine health monitoring solution for predictive maintenance that detects tiny metal traces within engine oil. This solution enables the identification of deterioration of key oil-wetted components, such as gears, bearings, and seals, well before a potential event occurs and without intrusive inspection.

Do: Preserve Your APU Properly During Downtime

If an APU will be inactive for an extended time, make sure to follow the preservation procedure described in the component maintenance manual, kept up to date on MyP&WC Power. This will help ensure the APU will deliver the same level of performance once you start using it again. Finally, take particular care when applying oil or another protective coating to any exposed areas that are prone to corrosion.

When in doubt, contact our Customer First Centre or your Field Support Representative.