What is PAPI azimuth alignment?
Turning each PAPI unit in the horizontal plane so its beam runs parallel to the runway centreline, toward the approaching aircraft.
Azimuth is the direction a PAPI unit points in the horizontal plane. The elevation angle tilts the beam up or down and fixes the height at which white changes to red; azimuth turns the unit left or right and fixes which part of the approach receives the signal.
Each of the four units is aimed so that its beam axis is parallel to the runway centreline and to the other three units. They are not toed in toward the runway or out away from it. A pilot on the extended centreline then sits well inside every beam, where the light is strongest and the red and white are cleanest.
An azimuth error does not move the glide path. It makes the turned unit look dimmer and reach less far for a pilot on the centreline, so the four lights no longer match. Because turning a unit on an uneven base can also change its elevation, the elevation is read again after the azimuth is set.
The unit is set by sighting along a reference line parallel to the centreline, with the unit’s own sighting device or a theodolite or total station, and turning it until it agrees. A hand compass is not a reliable reference this close to steel and cables.
Frequently Asked Questions
Q1What is PAPI azimuth alignment?
It is the horizontal aiming of each PAPI unit. The unit is turned left or right until its beam axis points along the approach, parallel to the runway centreline and to the other three units. It is separate from the elevation angle, which sets the height of the white-to-red change.
Q2Does azimuth set the glide path?
No. The glide path is set by the elevation angle of each unit. Azimuth decides which part of the approach receives the signal. A small azimuth error does not move the white-to-red change, but it makes that unit dimmer and shorter in range for a pilot on the centreline, and the four units no longer look equal.
Q3Which way should each unit point?
All four units point the same way, parallel to the runway centreline and toward the approaching aircraft. They are not toed in toward the runway or out away from it. Where the design uses an offset approach, the aiming direction is given in the design and the applicable standard.
Q4How is azimuth set and checked?
By sighting along a reference line that is parallel to the centreline, using the unit's own sighting device or a theodolite or total station, and turning the unit until it agrees. A hand compass is not a reliable reference this close to steel and cables. Read the elevation again afterwards, because turning a unit on an uneven base can change it.
Q5When does azimuth need to be checked again?
At installation, at commissioning, and after anything that could turn the unit: a strike, settlement or a loosened coupling, re-levelling, or work on the optics or housing. For the maintenance routine see the PAPI Alignment entry. Use the tolerance in the manufacturer's data and the applicable standard.
See It. Understand It. Then Learn How to Engineer It.
Recognising an AGL system visually is the first step. The next step is knowing how to design, install, test, commission and maintain them correctly.
Build Practical AGL Engineering Skills
Go deeper with structured training from Precision AGL Academy, covering:
Learn how each light, sign and circuit works as part of a complete airport lighting system, not just as an isolated diagram.