Pilot/Controller Glossary

the lateral limits of a runway. Runway lights are
uniformly spaced at intervals of approximately 200
feet, and the intensity may be controlled or preset.
c. Touchdown Zone Lighting- Two rows of
transverse light bars located symmetrically about the
runway centerline normally at 100 foot intervals. The
basic system extends 3,000 feet along the runway.
d. Runway Centerline Lighting- Flush centerline
lights spaced at 50-foot intervals beginning 75 feet
from the landing threshold and extending to within 75
feet of the opposite end of the runway.
e. Threshold Lights- Fixed green lights arranged
symmetrically left and right of the runway centerline,
identifying the runway threshold.
f. Runway End Identifier Lights (REIL)- Two
synchronized flashing lights, one on each side of the
runway threshold, which provide rapid and positive
identification of the approach end of a particular
runway.
g. Visual Approach Slope Indicator (VASI)- An
airport lighting facility providing vertical visual
approach slope guidance to aircraft during approach
to landing by radiating a directional pattern of high
intensity red and white focused light beams which
indicate to the pilot that he/she is "on path" if he/she
sees red/white, "above path" if white/white, and
"below path" if red/red. Some airports serving large
aircraft have three-bar VASIs which provide two
visual glide paths to the same runway.
h. Precision Approach Path Indicator (PAPI)- An
airport lighting facility, similar to VASI, providing
vertical approach slope guidance to aircraft during
approach to landing. PAPIs consist of a single row of
either two or four lights, normally installed on the left
side of the runway, and have an effective visual range
of about 5 miles during the day and up to 20 miles at
night. PAPIs radiate a directional pattern of high
intensity red and white focused light beams which
indicate that the pilot is "on path" if the pilot sees an
equal number of white lights and red lights, with
white to the left of the red; "above path" if the pilot
sees more white than red lights; and "below path" if
the pilot sees more red than white lights.
i. Boundary Lights- Lights defining the perimeter
of an airport or landing area.
(Refer to AIM.)

AIRPORT MARKING AIDS- Markings used on
runway and taxiway surfaces to identify a specific
runway, a runway threshold, a centerline, a hold line,

etc. A runway should be marked in accordance with
its present usage such as:
a. Visual.
b. Nonprecision instrument.
c. Precision instrument.
(Refer to AIM.)

AIRPORT REFERENCE POINT (ARP)- The
approximate geometric center of all usable runway
surfaces.
AIRPORT RESERVATION OFFICE- Office
responsible for monitoring the operation of slot
controlled airports. It receives and processes requests
for unscheduled operations at slot controlled airports.
AIRPORT ROTATING BEACON- A visual
NAVAID operated at many airports. At civil airports,
alternating white and green flashes indicate the
location of the airport. At military airports, the
beacons flash alternately white and green, but are
differentiated from civil beacons by dualpeaked (two
quick) white flashes between the green flashes.
(See INSTRUMENT FLIGHT RULES.)
(See SPECIAL VFR OPERATIONS.)
(See ICAO term AERODROME BEACON.)
(Refer to AIM.)

AIRPORT STREAM FILTER (ASF)- An on/off
filter that allows the conflict notification function to
be inhibited for arrival streams into single or multiple
airports to prevent nuisance alerts.
AIRPORT SURFACE DETECTION EQUIPMENT
(ASDE)- Surveillance equipment specifically designed to detect aircraft, vehicular traffic, and other
objects, on the surface of an airport, and to present the
image on a tower display. Used to augment visual
observation by tower personnel of aircraft and/or
vehicular movements on runways and taxiways.
There are three ASDE systems deployed in the NAS:
a. ASDE-3- a Surface Movement Radar.
b. ASDE-X- a system that uses an X-band
Surface Movement Radar, multilateration, and
ADS-B.
c. Airport Surface Surveillance Capability
(ASSC)- A system that uses Surface Movement
Radar, multilateration, and ADS-B.
AIRPORT SURVEILLANCE RADAR- Approach
control radar used to detect and display an aircraft"s
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.