Describe the normal steps of a typical APU start sequence.

• A. Confirm prestart conditions, energize starter, accelerate N2 toward self-sustaining speed, ignite fuel to light off, monitor EGT and oil pressure, and bring APU to stable operation with bleed air/electrical supply as required.
• B. Open main fuel valve
• C. Turn on lights
• D. Engage autopilot

Answer: (A)

Starting an APU follows a practical sequence that ensures safe, controlled light-off and power delivery. First, you confirm prestart conditions so the system has everything it needs and no faults are present. Then you energize the starter to spin the turbine and bring the N2 spool up toward a speed where the fuel control can sustain operation without the starter. Once the N2 reaches that self-sustaining point, fuel is commanded and light-off occurs, meaning the fuel-air mixture ignites and the turbine begins to run on its own. After light-off, you monitor critical parameters like exhaust gas temperature and oil pressure to confirm everything is within limits. If all looks good, you bring the APU to a stable operating state and provide the needed bleed air or electrical power to aircraft systems as required. Actions like opening a main fuel valve, turning on cabin lights, or engaging autopilot aren’t part of the normal start sequence and don’t contribute to bringing the APU online.