Fuel Systems
SAFETY SPOTLIGHT: Fuel Management
Know the fuel system of the airplane you fly. Some systems are quite simple, while others may be complex and include auxiliary and aftermarket tip tanks with electric boost and fuel transfer pumps. Pilots have made forced landings with fuel still available because they did not understand the system or operate it properly.
Fuel Pumps
Fuel pump configuration and use varies from one model to another, and sometimes within a model.
- High wing—In most carbureted high-wing designs, gravity feeds fuel from the tank to the engine. Most higher power and high-altitude, high-wing designs also have an auxiliary fuel pump.
- Low wing—If the fuel supply is lower than the engine, fuel must be pumped, and most low-wing designs have at least two fuel pumps. The main pump is usually mounted on the engine and driven mechanically. The auxiliary electric fuel pump in some designs must be on for landing and takeoff; in other designs it may be used for priming, high-altitude flight, or as an emergency backup should the mechanical pump fail.
Fuel Tanks
Fuel tanks are predominately metal, although some are synthetic rubber bladders. Generally, each tank has a capped opening for filling, a fuel line to the engine, and (in fuel-injected designs) a return line to convey excess fuel from the engine back to the tank. Tanks also have drains for fuel sampling and vents to admit air and prevent the tank from collapsing as fuel is consumed.
All airplanes have a means of selecting which tank or combination of tanks is in use and of shutting off all fuel to the engine. Some airplanes, such as the Cessna 150/152, feed from two tanks at the same time. The fuel selector valve has an On and an Off position. Others (like the Cessna 172) have Off, Left, Both, and Right fuel selector positions. Most low-wing singles are not able to feed from both wing tanks at the same time.
Fuel Gauge
Fuel quantity gauges range from a multifunction display in a glass panel cockpit to a cork-and-rod system protruding through the fuel cap in front of a Piper Cub’s windshield. Some fuel gauges include a yellow arc indicating usable fuel limited to cruise flight. This limitation exists because abrupt maneuvering on the ground or in the air could move fuel away from the tank’s outflow ports.