AVASI

The Abbreviated Visual Approach Slope Indicator (AVASI) is a simplified visual glide slope guidance system. Unlike the multi‑bar VASI or the four‑unit PAPI, AVASI typically consists of a single light bar or a simplified two‑bar configuration with fewer light units. It provides a basic but effective red/white indication to help pilots maintain a safe descent angle during final approach.

AVASI is designed for smaller airfields, heliports, and temporary operations where a full‑scale system is not economically or logistically justified. It offers a compact footprint, lower power consumption, and simpler installation while still delivering the essential visual cue needed for safe approaches.

AVASI exists to bring basic glide slope guidance to airfields and temporary operations where the cost, power requirements, or physical footprint of a full VASI or PAPI installation can't be justified. By reducing the light units to a single bar or simplified two-bar layout, it keeps the essential red/white on-path indication pilots need while cutting the infrastructure and maintenance burden considerably.

This trade-off is deliberate: AVASI accepts a coarser glide slope indication in exchange for being deployable at smaller general aviation fields, heliports, and short-term operations that would otherwise have no visual glide guidance at all, which is a meaningful safety improvement over relying on unaided visual approach judgement.

AVASI is deployed on a variety of smaller and specialised landing sites:

• General aviation airports – with low traffic volumes and limited budgets.
• Heliports – where a compact system is needed for helicopter approaches.
• Remote and regional airstrips – with limited electrical infrastructure.
• Military forward operating bases – requiring rapid deployment and simplicity.
• Temporary or emergency runways – where a lightweight, portable system is advantageous.
• As a backup to PAPI or VASI – on larger runways for additional redundancy.

AVASI reduces the standard VASI arrangement to a single light bar, mounted on one side of the runway at a fixed lateral offset from the edge, clear of the obstacle-limitation surface and any blast zone. The bar is set back from the threshold at the distance needed to place the resulting on-slope indication over the threshold at the correct height, tied into the runway centreline and threshold survey. Units sit on frangible mounts and are individually aimed and levelled during commissioning to give the correct red/white split at the design glide angle. Cabling runs underground back to the constant current regulator, and the single-bar footprint suits sites where space, budget, or traffic volume don't justify a full two-bar system.

AVASI operates on the same fundamental optical principle as VASI and PAPI, but with a simplified configuration:

• Configuration: AVASI typically uses a single bar of lights (or two bars in some configurations) installed on the left side of the runway or helipad. The bar contains one or more light units that project a beam with a distinct red/white transition.
• Colour Indication: The pilot sees a single bar that changes colour based on the viewing angle. The indication is typically:
  • All white – aircraft is above the glide path.
  • White/red transition (or one white, one red in two‑bar setups) – on the correct glide path.
  • All red – aircraft is below the glide path.
  In a two‑bar configuration, the indication is similar to a 2‑bar VASI but with fewer lights per bar, providing a coarser but still reliable reference.
• Power and Control: AVASI units are powered from the constant current series circuit via isolating transformers, with intensity controlled by the CCR (typically 3‑step). The reduced number of units means lower overall power demand.
• Integration: AVASI is typically deployed independently and can be easily integrated with the runway lighting system. It is often controlled manually or via a basic ALCMS interface.

AVASI's control logic is the same fixed-optics principle as full VASI, scaled down to a single bar (or two reduced bars). Each light unit's lens/shutter assembly is tilted at commissioning so its red/white transition falls at a specific elevation; where more than one unit or bar is fitted, they're aimed a fraction of a degree apart so the ensemble straddles the glide path. That aim is mechanical and permanent — nothing in the circuit changes which colour a unit shows. All units on a bar share a constant current series circuit through their own isolating transformers, and the CCR (often a basic 3-step unit, sometimes only manually switched) sets one brightness level for the whole bar; with the reduced unit count, total loop power demand is correspondingly lower than a full VASI or PAPI installation. Fault detection is loop-based as with any series circuit — a voltage rise at constant current signals an open lamp or failed transformer — and because AVASI is often deployed as a standalone installation rather than through a full ALCMS, that fault may be reported to only a basic local panel or noted on next inspection rather than flagged in real time to the tower.

Each AVASI bar is a wide, box-section housing in die-cast aluminium alloy or louvred galvanised steel, built the same way as a full VASI bar but deployed as a single downwind bar (or a simplified two-bar pair) rather than a full multi-bar system. The optics are split into an upper clear (white) glass and a lower red filter glass, precisely positioned so the beam transitions from white to red at the set glide-path angle, with a built-in levelling and pitch-adjustment mechanism used to aim the bar during commissioning. The housing mounts on a frangible mast set at a fixed, surveyed height beside the runway, engineered to shear away cleanly if struck. Cabling runs underground in conduit to an isolating transformer housed in a nearby base can, with sealed, direct-burial connectors and a drainage provision to keep the transformer and cable entries free of standing water.