Visual Approach Slope Indicator (VASI)/ Precision Approach Path

Indicator (PAPI)

VASI

assist pilots in the landing approach provides a color coded visual glidepath

using a system of lights positioned alongside the runway

ensures safety by providing a visual glidepath which clears all obstructions in the final approach area

VASI

descent, using the VASI, should not be initiated until the aircraft is visually aligned with the runway

these lights are visible from 3-5 miles during the day and up to 20 miles or more at night

each light is designed so that the light appears as either white or red, depending on the angle at which the lights are viewed

Types of VASI

2-Bar VASI 3-Bar VASI Tri-color VASI Pulsating VASI (PVASI) PAPI

2-Bar VASI

Two-bar VASI installations provide one visual glide path which is normally set at 3 degrees

2-Bar VASI

3-Bar VASI

•three-bar VASI installations provide two visual glide paths•lower glide path is provided by the near and middle bars and is normally set at 3 degrees•the upper glide path, provided by the middle and far bars, is normally 1/4 degree higher•higher glide path is intended for use only by high cockpit aircraft to provide a sufficient threshold crossing height

3-Bar VASI

When using a 3 bar VASI it is not necessary to use all three bars

The near and middle bars constitute a two bar VASI for using the lower glidepath

the middle and far bars constitute a 2 bar VASI for using the upper glidepath

Tri-color VASI

•normally consist of a single light unit projecting a three-color visual approach path into the final approach area of the runway•below glide path indication is red, • the above glide path indication is amber, •and the on glide path indication is green

Tri-color VASI

*errors are increased due to a major design shortcoming of the tri-colored VASI. While on approach, the color amber (above slope) can be seen at a very thin angle of approach between green (on slope) and red (below slope)•Despite this shortcoming, it is (reportedly) in widespread use in Eastern European countries, especially Russia and Ukraine.

Pulsating VASI (PVASI)

• normally consist of a single light unit projecting a two-color visual approach path into the final approach area of the runway• the on glide path indication is a steady white light • the slightly below glide path indication is a steady

red light • if the aircraft descends further below the glide

path, the red light starts to pulsate • the above glide path indication is a pulsating white

light

Pulsating VASI (PVASI)

Precision Approach Path Indicator (PAPI)

system is a simple and efficient, positive visual aid to the pilot on final approach

consists of a line of four units at 90˚ to the runway centre line which are typically spaced at 9 meters apart

either four or two identical light units placed on the left of the runway aimed outward into the approach zone

Precision Approach Path Indicator (PAPI)

provides the pilot with a safe and accurate glide slope on final approach to the runway

A row of PAPI light housing assemblies (LHAs) placed perpendicular to the approach path are seen by the pilot in combinations of red and white to indicate a path that is too high, too low or correctly on slope.

Precision Approach Path Indicator (PAPI)

An earlier glideslope indicator system, the Visual Approach Slope Indicator (VASI) is now obsolete and was deleted from Annex 14 in 1995

 The units are spaced 9 meters apart with the nearest unit 15 meters from the runway edge

PAPI can, if required, be located on the right hand side of the runway 

Precision Approach Path Indicator (PAPI)

In good visibility conditions the guidance information can be used at ranges up to five miles by day and night. At night the light bars can be seen at ranges of at least twenty miles

Precision Approach Path Indicator (PAPI)

To form the PAPI guidance signal the color transition boundaries of the four units are fixed at different angles› The lowest angle is used for the unit furthest from

the runway, the highest for the unit nearest to the runway

›  The designated glideslope is midway between the second and third light unit settings

Depending on the position of the aircraft relative to the specified angle of approach, the lights will appear either red or white to the pilot

PAPI