(2)
White and yellow-lighted water airport.

(3)
Green, yellow, and white-lighted heliport.

The number of flashes per minute from beacons identifying heliports is usually greater than the number of flashes per minute from beacons identifying airports. Military airport beacons flash alternately white and green, but are differentiated from civil airport beacons by dual peaked (two quick) white flashes between the green flashes.
AIRPORT SURFACE DETECTION EQUIPMENT/ASDE - Radar equipment specifically designed to detect all principal features on the surface of an airport, including aircraft and vehicular traffic and to present the entire image on a radar indicator console in the control tower. Used to augment visual observation by tower personnel of aircraft and/or vehicular movement on runways and taxiways.
(a) ASDE-X - The ASDE-X - provides seamless surveillance and aircraft identification to air traffic controllers. The system uses a combination of surface movement radar, transponder multilateration and Automatic Dependent Surveillance - Broadcast (ADS-B) sensors to display aircraft and vehicle positions on the airport surfaces, as well as of aircraft flying within five miles of the airport. The system provides improved surveillance information to tower personnel, who see this information presented as a color display of aircraft and vehicle positions overlaid on a map of the airport’s runways/taxiways and approach corridors.
AIRPORT SURVEILLANCE RADAR/ASR - Approach control radar used to detect and display an aircraft position in the terminal area. ASR provides range and azimuth information but does not provide elevation data. Coverage of the ASR can extend up to 60 miles.
AIRPORT TRAFFIC CONTROL SERVICE - A service provided by a control tower for aircraft operating on the movement area and in the vicinity of an airport. (See Movement Area, Tower)
AIR ROUTE SURVEILLANCE RADAR/ARSR - Air Route Traffic Control Center (ARTCC) radar, used primarily to detect and display an aircraft position while enroute between terminal areas. The ARSR enables controllers to provide radar Air Traffic Control service when aircraft are within the ARSR coverage. In some instances, ARSR may enable an ARTCC to provide terminal radar services similar to, but usually more limited, than those provided by a radar approach control.
AIR ROUTE TRAFFIC CONTROL CENTER/ARTCC - A facility established to provide Air Traffic Control service to aircraft operating on IFR flight plans within controlled airspace and principally during the enroute phase of flight. When equipment capabilities and controller workload permit, certain advisory/assistance services may be provided to VFR aircraft. (See NAS Stage A, Enroute Air Traffic Control Service)
AIRSPACE HIERARCHY (P/CG) - Within airspace classes, there is a hierarchy and, in the event of an overlap of airspace: Class A preempts Class B, Class B preempts Class C, Class C preempts Class D, Class D preempts Class E, and Class E preempts Class G.