Which statement best describes a normal indication that an APU is ready to supply bleed air or electrical power during standard ground operations?

Which statement best describes a normal indication that an APU is ready to supply bleed air or electrical power during standard ground operations?

• A. The APU shows no fault indications on the control system.
• B. The N2 speed is well above idle and the APU is producing a loud exhaust.
• C. Electrical output is within spec, N2 is at expected idle, EGT within limits, and there are no fault indications.
• D. The APU is running with a fault code displayed.

Answer: (C)

When an APU is ready to supply bleed air or electrical power, you’re looking for evidence that it’s operating correctly and within safe limits. The best sign is that electrical output is within specification, the N2 speed is at the expected idle range, the EGT is within limits, and there are no fault indications. This combination shows the APU can reliably generate power (electrical or bleed air) and that all critical operating parameters are in their normal, safe ranges. Just having no fault indications isn’t enough by itself—the APU could have an issue with output or speeds that isn’t being signaled as a fault, so you want to see the actual outputs and temperatures within spec. A high N2 with loud exhaust might indicate the unit is running, but it doesn’t guarantee the power output or thermal conditions are correct. A fault code displayed is a clear sign it’s not ready.

When an APU is ready to supply bleed air or electrical power, you’re looking for evidence that it’s operating correctly and within safe limits. The best sign is that electrical output is within specification, the N2 speed is at the expected idle range, the EGT is within limits, and there are no fault indications. This combination shows the APU can reliably generate power (electrical or bleed air) and that all critical operating parameters are in their normal, safe ranges.

Just having no fault indications isn’t enough by itself—the APU could have an issue with output or speeds that isn’t being signaled as a fault, so you want to see the actual outputs and temperatures within spec. A high N2 with loud exhaust might indicate the unit is running, but it doesn’t guarantee the power output or thermal conditions are correct. A fault code displayed is a clear sign it’s not ready.