When does the APU fuel pump operate?

When does the APU fuel pump operate?

• A. When the APU is running and there is no other source of fuel pressure
• B. When the APU is running
• C. When the engines are running
• D. When the aircraft is on the ground

Answer: (A)

The APU fuel pump is there to feed the APU with fuel only when it’s actually needed and there isn’t another source delivering pressure. It’s an electric pump that comes into service during APU start and continues to run as long as the APU is operating and there is no other fuel-pressure source supplying the APU. If the engine-driven pumps are providing adequate fuel pressure to the APU, the dedicated APU pump won’t run, conserving power and reducing unnecessary wear. That’s why the correct condition is when the APU is running and there’s no other source of fuel pressure. Being on the ground by itself or engines running does not by itself trigger the APU pump without considering the pressure source.

The APU fuel pump is there to feed the APU with fuel only when it’s actually needed and there isn’t another source delivering pressure. It’s an electric pump that comes into service during APU start and continues to run as long as the APU is operating and there is no other fuel-pressure source supplying the APU. If the engine-driven pumps are providing adequate fuel pressure to the APU, the dedicated APU pump won’t run, conserving power and reducing unnecessary wear. That’s why the correct condition is when the APU is running and there’s no other source of fuel pressure. Being on the ground by itself or engines running does not by itself trigger the APU pump without considering the pressure source.