GSE is there to support the operations of aircraft on the ground. It involves ground power, aircraft mobility, and loading operations for both cargo and passengers. Passengers can board aircraft using aircraft stairs or mobile passenger stairs. At more active airports, the use of passenger loading bridges is becoming common. Providing a fixed ground power unit and preconditioned air for each gate position is highly recommended for environmental issue. Fueling and power systems are fixed utilities located at aircraft parking. The main advantage of underground hydrant system is the reduction of ground support equipment servicing the aircraft on the parking.