When are boost pumps typically used in the fuel system?

• A. To ensure positive fuel pressure to the engine-driven pumps during start or when low tank pressure is encountered.
• B. During normal cruise.
• C. When landing gear is down.
• D. Only during refueling.

Answer: (A)

Boost pumps provide a positive, pressurized fuel supply to the engine-driven pumps. Their main job is to prime the system and keep fuel flowing when the engine-driven pumps would otherwise see insufficient suction or during engine start.

During start, the engine-driven pumps aren’t yet producing pressure, so the boost pumps push fuel into the lines to prime them and ensure the engines receive fuel promptly. If tank pressure drops—for example when fuel is far from the engines or under certain flight conditions—the boost pumps boost pressure to prevent fuel starvation. In normal cruise, the engine-driven pumps typically maintain adequate pressure on their own, so boost pumps aren’t required continually. They aren’t tied to landing gear position and aren’t limited to refueling operations.

So, boost pumps are typically used to ensure positive fuel pressure to the engine-driven pumps during start or when low tank pressure is encountered.