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Pilot/Controller Glossary

3/29/18

PCG A−8

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 de-

signed 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.
AIRPORT TAXI CHARTS−

(See AERONAUTICAL CHART.)