What is an AVASI?
The abbreviated VASI: just two light units, one near and one far, each splitting its beam into white above and red below. The pilot reads red over white on the slope.
An AVASI is the abbreviated VASI. Where a full VASI uses several light units in each bar, an AVASI uses just two light units on one side of the runway, one near bar and one far bar. It is read in the same way as a two-bar VASI.
1Each unit splits its beam
Each unit sends out a beam that is white above its setting angle and red below it. The pilot reads only the colour of each unit, not its brightness or distance, and needs no instrument.
2The far unit is set higher: red over white
The far unit is aimed higher than the near unit. Descending, the pilot first sees both white, then the far unit turns red to give red over white, the on-slope signal, and finally both red. The pilot's memory aid is “red over white, you’re all right”.
3Know where it stands, and check what remains
An AVASI is a legacy system: new work normally uses a PAPI or an APAPI, and current ICAO Annex 14 specifies PAPI and APAPI as the standard visual approach slope indicators, not the AVASI, so an existing AVASI is kept to its original design and the authority’s requirements. Check that each unit shows a sharp white-to-red change, that the far unit is still set higher than the near one, that both are aimed as designed and equal in brightness, and that nothing blocks or dirties the beam. A shifted unit or dirty lens gives a false slope indication. Do not confuse it with an APAPI: that also has two units, but side by side in one row, and its on-slope signal is the unit nearer the runway red and the farther one white.
| Element | Setting or signal | Effect on the pilot's view |
|---|---|---|
| Near unit | Lower setting angle | Turns red second on descent |
| Far unit | Higher setting angle | Turns red first on descent |
| Above both settings | Both units white | Above the slope |
| Between the settings | Far red, near white | On the slope |
| Below both settings | Both units red | Below the slope |
Frequently Asked Questions
Q1What is an AVASI?
An AVASI is the abbreviated form of the VASI. It uses only two light units on one side of the runway, one near bar and one far bar, instead of the full set of units in each bar. Each unit splits its beam into white above and red below, and the display is read in the same way as a two-bar VASI.
Q2How is an AVASI read?
Above the slope both units show white. On the slope the far unit shows red and the near unit shows white, red over white. Below the slope both show red. The far unit is set higher than the near unit, so it turns red first as the aircraft descends.
Q3Is the AVASI still used?
Some AVASI installations remain in service, but new work normally uses a PAPI or an APAPI, and current ICAO Annex 14 specifies PAPI and APAPI as the standard visual approach slope indicators, not the AVASI. Keep an existing AVASI to its original design and the authority's requirements, and confirm the position with the authority before any change.
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