Hydrant System in Aircraft

Typical Fixed Aircraft Fuel Hydrant System

The National Fire Protection Association NFPA 407 Standard for Aircraft Fuel Servicing describes aircraft fuel servicing as the transfer of a flammable or combustible liquid fuel between a bulk storage system and the fuel tanks of an aircraft.

The transfer is usually accomplished by using a tank vehicle, a hydrant vehicle, a hydrant cart, a fuel servicing cabinet, or a fueling pit. Drums and pumps are sometimes used. Acknowledging there are other alternatives to hydrant fueling of aircraft, we will focus only on the fixed system in our discussion. Fixed hydrant systems are typically found at larger international airports.

A cost benefit analysis should be performed to determine the best type of system for any given situation. Where large volumes of fuel are being regularly transferred into aircraft the fixed hydrant system should be strongly considered. However, a fixed hydrant system can often be justified by providing a safer means of fueling aircraft than can be achieved by having large refueler trucks negotiate very congested aircraft parking aprons or tarmacs.

Fuel Hydrant System

The typical Airport Hydrant System can be divided into three major subsystems; 1) Inbound or receiving system, 2) storage system, and 3) dispensing or delivery system.

Kerosene based turbine fuels are considered to be combustible liquids while aviation gasoline (avgas) is a volatile flammable liquid. Aviation gasoline has a flash point of approximately -46oC (-50oF), while Jet A and other kerosene grade turbine fuels have a minimum flash point of 38oC (100oF).

Flash point is the lowest temperature at which the vapors above a flammable liquid will ignite upon the application of an ignition source. Aviation gasoline produces large volumes of vapor and is capable of forming ignitable mixtures with air even at very low temperatures. Jet A and other kerosene grades of turbine fuel do not produce ignitable mixtures with air at normal temperatures and pressures, but when Jet A turbine fuel is heated above its flash point or exists in the form of a mist the mixture can be ignited. This condition can develop where temperatures are 38oC (100oF) or higher.