What is misalignment?
An asset that has moved from the position, level or aiming it was installed to — rotated, tilted, settled or re-aimed — and how an inspector decides how far out it is.
Misalignment means an asset is no longer where or how it was installed to be. A fixture has rotated or tilted so its beam is off-axis, a base can has settled or heaved, a PAPI unit's aiming has changed, an approach light has leant over, or a sign no longer faces the viewer. The asset can look completely intact.
Misalignment is a function problem, not a physical one: the light goes where it should not, or the face cannot be read as intended. A small, stable shift is recorded and monitored. An asset beyond its allowed limit is re-aligned, re-checked and the cause fixed. Where the asset gives guidance, such as a PAPI or an approach light, misalignment beyond tolerance can mislead a pilot and is critical: it is reported and made safe first.
The asset has moved from its designed position, level or aiming. It may be undamaged, and it is put right by re-aligning and re-checking, plus fixing what moved it.
Physical harm such as a crack, cut or crush. The asset is repaired or replaced, and a strike can cause both damage and misalignment together.
- Make the area safe. Work under the permit-to-work, with the circuit isolated where the procedure requires it.
- Record as found. Photographs and readings before touching anything, with date and location.
- Compare with the design. Check position, level, orientation and aiming against the as-installed record and the manufacturer's data.
- Measure the offset. Use the manufacturer's alignment tool or method to see how far out it is, and in which direction.
- Find what moved it. Strike, settlement, frost heave, loose fixings, snow clearance or earlier work not re-checked.
- Classify and act. Within tolerance, out of tolerance or critical, then record, re-align and re-check, or report and make safe, and fix the cause.
Frequently Asked Questions
Q1What does misalignment mean in AGL inspection?
An asset that has moved away from the position, orientation or aiming it was installed to, so it no longer shows its light or face the way the design intends. It is recorded, classified by how far it is out and what it affects, and acted on according to the site's procedures.
Q2How is misalignment different from damage?
Damage is physical harm such as a crack or crush. Misalignment is a change in position or aiming, and the asset can look perfectly intact. A fixture with an undamaged lens that has rotated on its base is misaligned, not damaged, though a strike can cause both.
Q3What causes misalignment of airfield lighting?
Aircraft and vehicle strikes, snow clearance, jet blast, frost heave and settlement, pavement movement or resurfacing, loose or worn fixings, and work done without re-checking the aiming afterwards. Finding the cause matters, or the asset moves again.
Q4Which assets does misalignment matter most for?
Those whose light is aimed or whose face must be read from a set direction: PAPI units, approach lights, in-pavement and elevated fixtures with directional beams, and signs. A PAPI that has moved can give pilots a wrong glide-path indication, so it is treated as a safety matter.
Q5How is misalignment classified?
By how far the asset is out and what it affects. Within tolerance means a small, stable shift that is recorded and monitored. Out of tolerance means the aiming, level or orientation is beyond the allowed limit and the asset is re-aligned, re-checked and the cause fixed. Critical means the asset could give misleading guidance, such as a PAPI or approach light, and it is reported and made safe first. The limits and the exact grading come from the manufacturer, the project specification and the site's inspection procedure.
Q6How is alignment checked?
With the manufacturer's alignment tool or method and the project's aiming data, compared against the as-installed record. Where the system requires it, such as PAPI, the result is confirmed by the check the authority specifies. Photographs and readings taken as found are kept so drift can be compared next cycle.
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