Pilot/Controller Glossary 

5/19/22 

AIRPORT DEPARTURE RATE (ADR)

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 A dynamic 

parameter specifying the number of aircraft which 
can depart an airport and the airspace can accept per 
hour. 

AIRPORT ELEVATION

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 The highest point of an 

airport’s usable runways measured in feet from mean 
sea level. 

(See TOUCHDOWN ZONE ELEVATION.) 
(See ICAO term AERODROME ELEVATION.) 

AIRPORT LIGHTING

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  Various lighting aids that 

may be installed on an airport. Types of airport 
lighting include: 

a. 

Approach Light System (ALS)

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 An airport 

lighting facility which provides visual guidance to 
landing aircraft by radiating light beams in a 
directional pattern by which the pilot aligns the 
aircraft with the extended centerline of the runway on 
his/her final approach for landing. Condenser-
Discharge Sequential Flashing Lights/Sequenced 
Flashing Lights may be installed in conjunction with 
the ALS at some airports. Types of Approach Light 
Systems are: 

1. 

ALSF-1

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 Approach Light System with 

Sequenced Flashing Lights in ILS Cat-I configura-
tion. 

2. 

ALSF-2

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 Approach Light System with 

Sequenced Flashing Lights in ILS Cat-II configura-
tion. The ALSF-2 may operate as an SSALR when 
weather conditions permit. 

3. 

SSALF

−

 Simplified Short Approach Light 

System with Sequenced Flashing Lights. 

4. 

SSALR

−

 Simplified Short Approach Light 

System with Runway Alignment Indicator Lights. 

5. 

MALSF

−

 Medium Intensity Approach Light 

System with Sequenced Flashing Lights. 

6. 

MALSR

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 Medium Intensity Approach Light 

System with Runway Alignment Indicator Lights. 

7. 

RLLS

−

  Runway Lead-in Light System 

Consists of one or more series of flashing lights 
installed at or near ground level that provides positive 
visual guidance along an approach path, either 
curving or straight, where special problems exist with 
hazardous terrain, obstructions, or noise abatement 
procedures. 

8. 

RAIL

−

 Runway Alignment Indicator Lights

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Sequenced Flashing Lights which are installed only 
in combination with other light systems. 

9. 

ODALS

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 Omnidirectional Approach Light-

ing System consists of seven omnidirectional 
flashing lights located in the approach area of a 
nonprecision runway. Five lights are located on the 
runway centerline extended with the first light 
located 300 feet from the threshold and extending at 
equal intervals up to 1,500 feet from the threshold. 
The other two lights are located, one on each side of 
the runway threshold, at a lateral distance of 40 feet 
from the runway edge, or 75 feet from the runway 
edge when installed on a runway equipped with a 
VASI. 

(Refer to FAA Order JO 6850.2, VISUAL 

GUIDANCE LIGHTING SYSTEMS.) 

b. 

Runway Lights/Runway Edge Lights

−

 Lights 

having a prescribed angle of emission used to define 
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 

PCG A

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