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Pilot Controlled Lighting PAPI - Precision Approach Path Indicator

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Overview

The PCL-PAPI Precision Approach Path Indicator (PAPI) is a ground-based visual aid designed to assist pilots in maintaining a safe and consistent glide path during the final approach to landing at airports and heliports. This system utilizes a multi-light unit that projects two distinct colors—red & white—to indicate the pilot’s position relative to the desired glide slope. The system is intended for use at small airfields or heliports where simplicity and cost-effectiveness are prioritized over more expensive complex systems. Comes in a 2 fixture(shown here) and 4 fixture versions.

What is a Two-Fixture PAPI?
A Precision Approach Path Indicator (PAPI) is a visual aid that helps pilots maintain the correct glide path during final approach and landing. A standard PAPI installation often uses four light units arranged in a row, but a two-fixture PAPI is a simplified version that provides the same essential guidance with fewer lights. The system is intended for use at small airfields or heliports where simplicity and cost-effectiveness are prioritized over more expensive complex systems. Comes in a 2 fixture(shown here) and 4 fixture versions.

How it Works
Each light unit produces two overlapping beams: one red (seen from lower angles) and one white (seen from higher angles).

By aligning the lights at different vertical angles, the pilot sees a combination of red and white depending on their position:
- Two White: Aircraft is above the glide path.
- One White / One Red: Aircraft is on the glide path.
- Two Red: Aircraft is below the glide path.

This simple three-state system gives the pilot an instant, intuitive indication of whether to correct their descent.

Advantages of a Two-Fixture PAPI
Compact and Cost-Effective: Fewer lights mean lower installation and maintenance costs compared to a four-light PAPI.

Ease of Installation: Requires less runway edge space and simpler electrical setup.

Clearer Guidance than Tri-Color VASI:
- A tri-color VASI uses a single fixture that shifts between amber, green, and red. While compact, it can be harder to interpret quickly and may suffer from “color blur” under certain conditions.
- A two-fixture PAPI gives discrete red/white indications, which are less ambiguous and easier to read in poor visibility or at a distance.

Better Pilot Familiarity: PAPIs (two or four unit) are widely used worldwide, so pilots are generally more comfortable with the red/white indication system than with tricolor VASIs.

Comparison: Two-Fixture PAPI vs. Tri-Color VASI

Feature Two-Fixture PAPI Tri-Color VASI
Light Units 2 fixtures 1 fixture
Indications Red / White combinations Amber / Green / Red
Ease of Interpretation Simple, discrete steps (above, on, below) Can be less intuitive, colors can blur
Pilot Familiarity Very high (standardized worldwide) Moderate, less common today
Cost & Installation Moderate Lower
Accuracy Higher precision, even with 2 units Less precise, especially at longer distances


A two-fixture PAPI strikes a balance: it is simpler and more affordable than a four-unit PAPI, while still providing clearer, more precise guidance than a tri-color VASI. If ultra precision is needed, perhaps for a short field relative to the aircraft landing, or high precision is required for other reasons, then the 4 fixture version is the way to go. See our FAQ for more details on the comparisons.

Features

  • PAPI: Each fixture is a single optical assembly fixture containing a redundant high-intensity LED light source and a color-filtering mechanism to emit red or white light based on the viewing angle.
  • Mounting Structure: A stable, weather-resistant 3” Schedule 40 PVC pipe stand cemented 12” into the ground and standing 10” above ground for the airport version. 4” above ground for the heliport version.
  • Power Supply: Requires 100-240V AC, 50-60Hz power, consuming approximately 16 watts for 110v, and 24watts for the 220v which uses 12watt bulbs.
  • Alignment Mechanism: Adjustable mount to calibrate the PAPI’s vertical angle to match the intended glide slope (typically 3-5° for general aviation and 6–8° for a helipad). Adjustment available is +3° vertically for each mount version. Example: Airport 3° mount version adjusts from 3-5.5° vertically. Heliport 7° adjusts from 7-10°. Custom mounts of any configuration are available.
  • Dual LED bulbs for redundancy. A single bulb still allows for an effective view at night.
  • Lenses – High quality lenses for increased optical clarity and transparency, designed specifically for outdoor use.

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https://www.youtube.com/embed/uveEoYar_PI?si=q8nHwYAWqaiijC6N

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Please note, Aircraft Spruce Australia's personnel are not certified aircraft mechanics and can only provide general support and ideas, which should not be relied upon or implemented in lieu of consulting an A&P or other qualified technician. Aircraft Spruce Australia assumes no responsibility or liability for any issue or problem which may arise from any repair, modification or other work done from this knowledge base. Any product eligibility information provided here is based on general application guides and we recommend always referring to your specific aircraft parts manual, the parts manufacturer or consulting with a qualified mechanic.