Aeronautical Information Manual (AIM), page 100

Index   99 -- Page 100 -- 101

AIM      CHG 2                                                                                                          3/15/07

   b. Precision Approach Path Indicator (PAPI).                    with the runway. The row of light units is normally
The precision approach path indicator (PAPI) uses                  installed on the left side of the runway and the glide
light units similar to the VASI but are installed in a             path indications are as depicted. Lateral course
single row of either two or four light units. These                guidance is provided by the runway or runway lights.
lights are visible from about 5 miles during the day               In certain circumstances, the safe obstruction
and up to 20 miles at night. The visual glide path of              clearance area may be reduced by narrowing the
the PAPI typically provides safe obstruction                       beam width or shortening the usable distance due to
clearance within plus or minus 10 degrees of the                   local limitations, or the PAPI may be offset from the
extended runway centerline and to 3.4 NM from the                  extended runway centerline. This will be noted in the
runway threshold. Descent, using the PAPI, should                  Chart Supplement U.S. and/or applicable NOTAMs.
not be initiated until the aircraft is visually aligned            (See FIG 2-1-5.)
                                                            FIG 2-1-5
                                       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)


   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 2-1-6
                                       Tri-Color Visual Approach Slope Indicator


                                                          e Gli          th
                                                        ov          e Pa                           Red
                                                      Ab On Glid
                                                             w  G lide P

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.

2-1-4                                                                                                    Airport Lighting Aids

Page 100 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   99 -- Page 100 -- 101