Which indicators would confirm an APU is ready to supply electrical power?

Which indicators would confirm an APU is ready to supply electrical power?

• A. Stable N2 within limits, EGT within limits, normal oil pressure, and a valid electrical output on the aircraft buses.
• B. High EGT, low N2, low oil pressure, and no electrical output.
• C. EGT within limits but N2 is high, oil pressure is low, and buses show partial power.
• D. Negative cooling oil temperature with erratic voltage readings.

Answer: (A)

When an APU is ready to supply electrical power, four things must be in the normal, healthy range: N2 speed, EGT, oil pressure, and actual electrical output on the aircraft buses. N2 within limits shows the APU is spinning at the correct speed and not under- or over-speeding. EGT within limits indicates the turbine/combustion process is operating at a safe temperature. Normal oil pressure means the lubrication system is functioning properly, keeping bearings protected during operation. And seeing valid electrical output on the aircraft buses confirms the generator is producing usable power and connected to the electrical system. If any of these readings are out of range or there’s no electrical output, the APU isn’t truly ready to supply power. For example, high EGT or out-of-range N2 suggests overheating or improper speed; low oil pressure points to potential mechanical failure; no electrical output means the generator isn’t delivering power. So the combination of proper speed, safe temperature, adequate lubrication, and confirmed electrical output is the best indication the APU is ready.

When an APU is ready to supply electrical power, four things must be in the normal, healthy range: N2 speed, EGT, oil pressure, and actual electrical output on the aircraft buses. N2 within limits shows the APU is spinning at the correct speed and not under- or over-speeding. EGT within limits indicates the turbine/combustion process is operating at a safe temperature. Normal oil pressure means the lubrication system is functioning properly, keeping bearings protected during operation. And seeing valid electrical output on the aircraft buses confirms the generator is producing usable power and connected to the electrical system.

If any of these readings are out of range or there’s no electrical output, the APU isn’t truly ready to supply power. For example, high EGT or out-of-range N2 suggests overheating or improper speed; low oil pressure points to potential mechanical failure; no electrical output means the generator isn’t delivering power. So the combination of proper speed, safe temperature, adequate lubrication, and confirmed electrical output is the best indication the APU is ready.