What is PAPI commissioning?
Siting, aiming and proving the approach path indicator — so the red and white signal a pilot sees marks the correct glide path.
A PAPI shows the pilot red or white according to height on the approach. Because each unit changes colour at its own elevation angle, commissioning proves the units are sited, levelled and aimed exactly to the design, and that the circuit and brightness steps work.
The signal is then checked from the approach path, and a flight check confirms the glide path as a pilot sees it. Each result is recorded. A defect is re-aimed or fixed and re-tested. When the checks pass, the PAPI is ready for acceptance.
- Siting. Confirm each unit's position and offset against the design layout.
- Level and aim. Level each unit, set its elevation angle with a calibrated instrument and check its azimuth.
- Electrical. After continuity and insulation tests, energise the circuit; check brightness steps and matching output.
- Signal check. View the red and white transition from the approach; check obstacles.
- Flight check. Use flight inspection to confirm the glide path and transition.
- Record. Log angles and results; re-aim, fix and re-test any defect.
Frequently Asked Questions
Q1What is PAPI commissioning?
The set of checks that prove a precision approach path indicator is correctly sited, aimed and working before it is used by pilots: position, levelling and aiming of each unit, electrical operation, the signal seen from the approach, and a flight check of the glide path.
Q2What do the PAPI units show a pilot?
A row of units beside the runway shows red or white depending on the pilot's height on the approach. All white means too high, all red means too low, and two white with two red shows the aircraft is on the correct glide path; three white with one red is slightly high and one white with three red is slightly low.
Q3Why is aiming the units so important?
Each unit changes from white to red at its own elevation angle. A small aiming error shifts the glide path the pilot sees, so every unit is levelled and set to its design angle with a calibrated instrument and the setting is recorded.
Q4What is checked on the ground?
The position of the units against the design, firm mounting and levelling, aiming angle of each unit, the circuit and brightness steps, and the red and white transition as seen from the approach path, with attention to any object that penetrates the PAPI obstacle protection surface.
Q5Why is a flight check needed?
Ground checks prove the units are set to the design angles, but only an aircraft can show the signal exactly as a pilot sees it. Flight inspection confirms the glide path and the transition between red and white against the design.
Q6What happens if a PAPI check fails?
The defect is recorded, the unit is isolated or re-aimed, the cause is corrected, and the affected checks are repeated, including any needed flight check. The record keeps the failure, the correction and the passing re-test.
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