Fuel Pumps. Fuel pumps, including auxiliary, hand, and engine driven, may be time replacement items. The
time replacement schedule is given in applicable inspection requirements manual. When pumps are removed for
replacement, fittings and plugs shall remain with aircraft for use on replacement pump.
Auxiliary. The auxiliary (booster) pump is mounted at the tank outlet within a detachable sump, or is
submerged in fuel at the bottom of the tank. The auxiliary pump, as shown in figure 2-4, supplies fuel under pressure to
the inlet of the engine-driven fuel pump. This type of pump is an essential part of the fuel system, particularly at high
altitudes, to keep the pressure on the suction side of the engine-driven pump from becoming low enough to permit the
fuel to boil. This booster pump is also used to transfer fuel from one tank
Figure 2-4. Auxiliary (Booster) Fuel Pump
to another, to supply fuel under pressure for priming when starting the engine, and, as an emergency unit, to supply fuel
to the carburetor in case the engine-driven pump fails. As a precautionary measure, the booster pump is always turned
on during takeoffs and landings to ensure a positive supply of fuel.
Hand. The hand, or wobble, pump is frequently used on light aircraft. It is generally located near other
fuel system components and operated from the cockpit by suitable controls. No current Army aircraft have hand pumps.
Engine-driven. The engine-driven pump is usually mounted on the accessory section of the engine. The
purpose of the engine-driven fuel pump is to deliver a continuous supply of fuel at the proper pressure at all times during
engine operation. The pump widely used at the present time is the positive-displacement, rotary-vane-type pump as
shown in figure 2-5.
Fuel Sumps. Usually a sump and drain are provided at the lowest point in the fuel tank for the accumulation of
contaminants. These sumps must be drained prior to flight to inspect for fuel contamination.
Figure 2-5. Engine-Driven Fuel Pump