PAPI and VASI

[Cessna172]

Just a quick question: how do you tell PAPIs from VASIs? I know that PAPI stands for Precision Approach Position Indicators and VASI stands for Visual Approach Position Indicators, but does the fact that a set of indicators are set up vertically or horizontally determine whether you call them PAPIs or VASIs?

Thanks!

[Jason]

Just a quick question: how do you tell PAPIs from VASIs? I know that PAPI stands for Precision Approach Position Indicators and VASI stands for Visual Approach Position Indicators, but does the fact that a set of indicators are set up vertically or horizontally determine whether you call them PAPIs or VASIs?

Thanks!

A PAPI uses light units similar to the VASI but are installed in a single row of either two or four light units.  The VASI is a system of lights so arranged to provide visual descent guidance information during the approach to a runway in multiple light bar rows.

Check out AIM Chatper 2, Section 1-2 for a visual picture.  The section also discusses the systems in greater detail.

A 2-bar VASI:

A PAPI:

[bcrosby]

The key here is the first letter.. P for PAPI and V for VASI..

Precision versus Visual

The PAPI offers better precision of your position on the glide path.. As with the VASI its either just "too high" or "too low".

[Jason]

The key here is the first letter.. P for PAPI and V for VASI..

Precision versus Visual

The PAPI offers better precision of your position on the glide path.. As with the VASI its either just "too high" or "too low".

Not necessarily true.... The VASI will tell you if you are below, above, or on the glidepath; not just if you're above or below it.

A 2-light unit PAPI provides the same information as a VASI does, but a 4-light unit PAPI offers more precise information by telling you if you are below glidepath, slightly below glidepath, on glidepath, slightly above glidepath, or above glidepath (two more things than the VASI tells you).

[Cessna172]

Thanks guys! That really helps! Nice visuals, Jason...

Cessna172