Fuel system layout: feed, pumps, strainer and drains
Small aircraft use one of two fuel systems (PHAK ch.7).
| System | Tank position | Typical |
|---|---|---|
| Gravity-feed | Above the carburettor; fuel flows down on its own | High-wing |
| Fuel-pump | Below the carburettor; gravity cannot move fuel | Low-wing (wing tanks) |
Fuel-pump system: two pumps.
| Pump | Drive | Used for |
|---|---|---|
| Main | Engine driven | n/a |
| Auxiliary (boost) | Electric, flight-deck switch | Engine starting; if engine pump fails |
Tanks:
- Normally inside the wings.
- Each has a filler opening on top of the wing, closed by a cap.
Strainer and sump:
- Strainer: after tank, before carburettor. Removes moisture and sediment.
- Sump: low point in fuel system or tank. Strainer assembly has one at its bottom, where contaminants settle.
Drains:
- Tank water may not appear at the strainer until fuel in the line from the tank has drained.
- Drain enough fuel to be sure it comes from the tank.
Trap: clear first drain can still be line fuel, not tank fuel.
References
- FAA-H-8083-25 PHAK ch.7 (Fuel Systems: Gravity-Feed, Fuel-Pump, Fuel Tanks, Fuel Strainers, Sumps, and Drains)