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Airport Lighting Aids

b. Precision Approach Path Indicator (PAPI).

The precision approach path indicator (PAPI) uses

light units similar to the VASI but are installed in a

single row of either two or four light units. These

lights are visible from about 5 miles during the day

and up to 20 miles at night. The visual glide path of

the PAPI typically provides safe obstruction

clearance within plus or minus 10 degrees of the

extended runway centerline and to 3.4 NM from the

runway threshold. Descent, using the PAPI, should

not be initiated until the aircraft is visually aligned

with the runway. The row of light units is normally

installed on the left side of the runway and the glide

path indications are as depicted. Lateral course

guidance is provided by the runway or runway lights.

In certain circumstances, the safe obstruction

clearance area may be reduced by narrowing the

beam width or shortening the usable distance due to

local limitations, or the PAPI may be offset from the

extended runway centerline. This will be noted in the

Chart Supplement U.S. and/or applicable NOTAMs.

(See FIG 2−1−5.)

FIG 2−1−5

Precision Approach Path Indicator (PAPI)

Slightly High

(3.2 Degrees)




(More Than

3,5 Degrees)

On Glide Path

(3 Degrees)

Slightly Low

(2.8 Degrees)


(Less Than

2.5 Degrees)

c. Tri−color Systems. Tri−color visual approach

slope indicators normally consist of a single light unit

projecting a three−color visual approach path into the

final approach area of the runway upon which the

indicator is installed. The below glide path indication

is red, the above glide path indication is amber, and

the on glide path indication is green. These types of

indicators have a useful range of approximately

one−half to one mile during the day and up to

five miles at night depending upon the visibility

conditions. (See FIG 2−1−6.)

FIG 2−1−6

Tri−Color Visual Approach Slope Indicator


Above Glide Path

On Glide Path

Below Glide Path





1. Since the tri−color VASI consists of a single light source which could possibly be confused with other light sources, pilots

should exercise care to properly locate and identify the light signal.