What is fixture alignment?

Fixture alignment is how precisely a runway light is aimed once it faces the right way. It has two parts: rotation, so the beam runs parallel to the runway axis, and tilt, so the beam sits at the vertical angle intended for the pilot's low view along the approach and runway. Runway light beams are shaped to cover that view and little more, so a small error can move the beam off the pilot's line of sight.

Inset lights are aligned with the runway axis using the fixture's alignment mark or reference, often with an alignment tool or jig set from a surveyed line, and sit level in the pavement. Elevated lights are levelled and aimed on a frangible mount. Alignment is rechecked after replacement, resurfacing or grooving, impact or jet blast, and during routine inspection, by eye from the approach and, where needed, by photometric measurement.

This follows fixture orientation (Entry 33): orientation is which way a fixture faces, alignment is how accurately. It matters most for the narrow beams described in the runway centreline beam (Entry 29) and TDZ beam (Entry 32). A misaligned light still shows, but it looks dim or is not seen from where it should be, which is why alignment faults are easy to miss without checking.