How is a PAPI tested?
Five checks that prove each unit is sound, set at the right angle, aimed down the runway and changing colour exactly where it should.
A PAPI is only as good as its aiming. Testing proves that all four units are electrically sound, set at the correct elevation angle, aimed parallel to the runway centreline, and showing a sharp white-to-red change at that angle.
The four units sit at the nominal slope angle plus and minus 10′ and 30′. For a 3° slope that is 2°30′, 2°50′, 3°10′ and 3°30′, with the highest setting nearest the runway. The final proof is a flight inspection, because only an aircraft on the approach confirms what the pilot actually sees.
Frequently Asked Questions
Q1What is PAPI testing?
Proving that a Precision Approach Path Indicator guides pilots correctly. Each of the four units is checked for electrical condition, elevation angle, azimuth aiming and a sharp white-to-red colour change, and the system is then confirmed by flight inspection.
Q2How is the elevation angle checked?
With an inclinometer placed on the unit's measuring surface. The four units are set at the nominal slope angle plus and minus 10 and 30 arcminutes. For a 3 degree slope that is 2°30′, 2°50′, 3°10′ and 3°30′, with the highest setting nearest the runway.
Q3Why does the colour transition matter?
A PAPI works because each unit changes sharply from white to red at its setting angle. A wide or blurred transition makes the pilot's cue vague, so the transition is checked as well as the angle itself.
Q4When is a PAPI tested?
At commissioning, at regular intervals under the airport's maintenance programme, and after any event that could disturb it: lamp or optics replacement, a unit being knocked, ground settlement, or work on the runway or its slope.
Q5Is a flight check needed?
Ground measurements prove the settings, but the final proof is flight inspection, where an aircraft flies the approach and confirms the colour changes happen at the intended angles. Its timing follows the national regulator and the airport's programme.
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