Which condition triggers the APU fuel pump to operate?

Which condition triggers the APU fuel pump to 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 engine is starting
• D. When the wing tanks are empty

Answer: (A)

The fuel supply to the APU is handled by a dedicated electric pump that serves as a backup source. It is designed to come on only when the APU is running and there is no other fuel pressure available from the engine-driven pumps or crossfeeds. This ensures the APU has a reliable supply to start and operate, but avoids unnecessary pumping when the main fuel system is already providing pressure. That’s why the best choice is the condition where the APU is running and there is no other source of fuel pressure. If the engines or wing tanks are already supplying fuel pressure, the APU fuel pump isn’t needed. Merely the APU running isn’t sufficient, and starting the engine or empty wing tanks don’t by themselves trigger the APU pump.

The fuel supply to the APU is handled by a dedicated electric pump that serves as a backup source. It is designed to come on only when the APU is running and there is no other fuel pressure available from the engine-driven pumps or crossfeeds. This ensures the APU has a reliable supply to start and operate, but avoids unnecessary pumping when the main fuel system is already providing pressure.

That’s why the best choice is the condition where the APU is running and there is no other source of fuel pressure. If the engines or wing tanks are already supplying fuel pressure, the APU fuel pump isn’t needed. Merely the APU running isn’t sufficient, and starting the engine or empty wing tanks don’t by themselves trigger the APU pump.