Aircraft Systems
Chapter 31: Aircraft Fuel Systems
Technical General for Aviators — Capt. Pankaj Pahil
31.1 Aircraft Fuel
AVGAS (Aviation Gasoline): Used for piston engines. Graded by octane rating and color-
coded.
AVTUR (Aviation Turbine Fuel / Jet Fuel): Kerosene-based fuel used for gas turbine
engines. Its quality is defined by properties like flashpoint and freezing point. Additives are
mixed in, including an icing inhibitor (FSII) and a static dissipator.
32.2 Fuel Tanks and System Components
Tank Types:
Integral Tanks: The most common type on large aircraft, where a sealed-off section of the
wing or fuselage structure (the "wing box") is used as the fuel tank.
Rigid Tanks: A separate, self-contained tank fitted into a compartment.
Flexible (Bladder) Tanks: A rubberized bag fitted into a structural cavity.
System Components:
Booster Pumps: Electric, centrifugal pumps located inside the tanks. They supply fuel under
low pressure from the tanks to the engine-driven pumps, preventing vapor lock at high
altitude.
Collector Tank (Feeder Box): A small compartment at the lowest point in the tank where
the booster pumps are located. It is designed to remain full of fuel during maneuvers to
prevent the pumps from running dry.
Baffles: Internal walls with holes that reduce the sloshing (surging) of fuel in the tanks.
Vent System: Allows air to enter and exit the tank as fuel is consumed or the aircraft
climbs/descends, preventing pressure differences. A vent/surge tank at the wingtip collects
any fuel that overflows into the vent lines.
Cross-feed and Shut-off Valves: A system of valves that allows fuel from any tank to be fed
to any engine, and allows engines/tanks to be isolated in case of a leak or fire.
Fuel Quantity Measurement: Modern aircraft use a capacitive fuel gauging system. It
measures the mass (weight) of the fuel, not the volume, which is much more accurate as fuel
density changes with temperature.