How do you determine APU readiness without an on-wing test?

How do you determine APU readiness without an on-wing test?

• A. Visual exterior condition is normal.
• B. The APU must be spinning at full speed to be ready.
• C. N2 speed must be high and EGT at maximum.
• D. Confirm normal electrical output, acceptable N2 and EGT readings, and no fault indications on the APU control system.

Answer: (D)

The main idea is that APU readiness without an on-wing test is established by what the APU reports about its own health and its actual operating readings, not by looks or running conditions alone. Confirming normal electrical output shows the APU can supply power to the aircraft’s systems. Checking that the N2 speed is within its proper operating range confirms the compressor-turbine section is spinning at a correct rate. Verifying that the EGT is within expected limits indicates the turbine inlet temperature is appropriate and not overheating. Finally, seeing no fault indications on the APU control system means the onboard diagnostics aren’t detecting faults in sensors, actuators, or logic. When all these indicators are normal, the APU is considered ready to perform essential functions without performing an on-wing test. Visual exterior condition doesn’t reveal internal health, and simply spinning at full speed doesn’t prove readiness to deliver power or be fault-free. Likewise, N2 speed that’s high or an EGT at maximum could signal abnormal or unsafe conditions rather than readiness. So the combination of normal electrical output, acceptable N2 and EGT readings, and no fault indications provides the reliable confirmation of APU readiness.

The main idea is that APU readiness without an on-wing test is established by what the APU reports about its own health and its actual operating readings, not by looks or running conditions alone. Confirming normal electrical output shows the APU can supply power to the aircraft’s systems. Checking that the N2 speed is within its proper operating range confirms the compressor-turbine section is spinning at a correct rate. Verifying that the EGT is within expected limits indicates the turbine inlet temperature is appropriate and not overheating. Finally, seeing no fault indications on the APU control system means the onboard diagnostics aren’t detecting faults in sensors, actuators, or logic. When all these indicators are normal, the APU is considered ready to perform essential functions without performing an on-wing test.

Visual exterior condition doesn’t reveal internal health, and simply spinning at full speed doesn’t prove readiness to deliver power or be fault-free. Likewise, N2 speed that’s high or an EGT at maximum could signal abnormal or unsafe conditions rather than readiness. So the combination of normal electrical output, acceptable N2 and EGT readings, and no fault indications provides the reliable confirmation of APU readiness.