FAA Aviation Mechanic Airframe (AMA)Fuel, Cabin and Ice Control SystemsMedium
During a 100-hour inspection, a technician checks the fuel tank sump quick-drain valves on a light aircraft. What is the primary purpose of these valves?
- ARelieve excess fuel tank pressure during refueling
- BAllow water and sediment to be drained from the low point of the tank
- CProvide a test port for fuel quantity calibration
- DVent fuel vapors overboard during climb
Show answer & explanationAnswer & explanation
Correct answer: B. Allow water and sediment to be drained from the low point of the tank
Water and sediment settle to the lowest point of the fuel tank because they are denser than fuel; the sump quick-drain valve allows this contamination to be sampled and removed before flight.
Why the other options are wrong
- A. Pressure relief is handled by vent systems, not sump drains.
- C. Quantity calibration is unrelated to sump drain function.
- D. Vapor venting is handled by the fuel tank vent system, not sump drains.
Fuel Tank Sump Drain
A quick-drain valve located at the lowest point of a fuel tank used to remove water and sediment contamination.
- Located at tank low points
- Checked during preflight and inspections
- Prevents water contamination from reaching the engine
Memory trick: Water sinks, sumps drink it out before it hits the engine.