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AIM 

6/17/21 

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

Precision Approach Path Indicator (PAPI) 

High 

Slightly High 

On Glide Path 

Slightly Low 

Low 

(More Than 

(3.2 Degrees) 

(3 Degrees) 

(2.8 Degrees) 

(Less Than 

3,5 Degrees) 

2.5 Degrees) 

White 

Red 

c.  Tri

color Systems. 

Tri

color visual approach 

the on glide path indication is green. These types of 

slope indicators normally consist of a single light unit 

indicators have a useful range of approximately 

projecting a three

color visual approach path into the 

one

half to one mile during the day and up to 

final approach area of the runway upon which the 

five miles at night depending upon the visibility 

indicator is installed. The below glide path indication 

conditions. (See FIG 2

1

6.) 

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

FIG 2

1

Tri

Color Visual Approach Slope Indicator 

Amber 

Above Glide Path

On Glide Path

Below Glide Path 

Amber 

Green 

Red 

NOTE

 

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. 

Airport Lighting Aids 

2

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