If motive flow is lost, how are the collector tanks kept full?

• A. Gravity feed lines
• B. Additional boost pumps
• C. Mirror flow
• D. There is no way

Answer: (A)

When motive flow is lost, the system relies on gravity to keep the collector tanks full. The fuel in the main wings sits at a higher elevation than the collector tanks, and gravity feed lines provide a passive path for fuel to move downward into the collectors. This uses the hydrostatic pressure created by the height difference, so the collectors remain fed even without pump-driven flow. Check valves and routing ensure fuel moves in the intended direction and prevents siphoning or unintended transfer. As long as there is fuel in the higher tanks and no obstruction, gravity will maintain the level in the collector tanks until the source tanks are emptied. Boost pumps or other pumped flow can’t substitute here because motive flow is unavailable, and the gravity path is the passive mechanism designed for this exact situation.