Towing Aircraft

It is often necessary to move an aircraft without starting the engines: for example, to position it for servicing or to enable passengers or cargo to be loaded.  If this operation is not carried out properly, severe damage can be caused to the aircraft.

If it is necessary for untrained or inexperienced persons to help move the aircraft, the person taking charge should instruct them thoroughly before starting so that they fully appreciate what they are required to do.

Detailed information relating to the movement of a particular aircraft will be found in the Manufacturers Maintenance Manual for the aircraft concerned.

Electrically operated Fuel Pumps

Electrically operated fuel pumps are used to move fuel throughout the fuel system, the power source being ac or dc.  However, 3-phase ac is mainly used in modern aircraft because of the high flow rates that can be achieved from relatively small pumps.

The pumps are normally situated inside the fuel tanks and are used to supply fuel under low pressure (approximately 20 psi) to the engines.

These pumps are usually called BOOSTER PUMPS when supplying fuel to the engines and TRANSFER PUMPS when used to transfer fuel between tanks.  However, both these functions are often combined and they can also have a jettison facility added, where they then may also be called JETTISON PUMPS.

The pumps have a centrifugal impeller which provides a low pressure supply of fuel to the engine inlet connection.

The flow of fuel will depend on the engine demand and is not therefore dependent on pump speed.  When the flow requirement is small the fuel will simply recirculate within the pump maintaining a low pressure supply, without the need for a pressure relief valve. These are not positive displacement pumps