What is a common troubleshooting step if the APU fails to start?

A common troubleshooting step if the Auxiliary Power Unit (APU) fails to start is to check the fuel supply and electrical connections. This is because both fuel supply issues and electrical connection problems are fundamental factors that can prevent the APU from starting successfully.

The APU requires an adequate supply of fuel to ignite and operate, so verifying that the fuel tanks are full and that there are no blockages or leaks in the fuel lines is crucial. Additionally, electrical connections must be intact and functioning because the APU needs a proper electrical supply to activate its starting system, including the starter motor and ignition system. Ensuring that there are no loose connections, damaged wiring, or faulty components can address many common starting failures.

Other troubleshooting steps might involve checking hydraulic systems or considering operational loads, but these are typically less immediate concerns compared to confirming that the fuel and electrical systems are working correctly. Furthermore, replacing the APU entirely would be considered a last resort after all simpler troubleshooting steps have been exhausted. Therefore, checking the fuel supply and electrical connections is a logical and standard first step in addressing APU starting issues.