What is civil tolerance?
How far the civil works under a light may differ from the design — position, level, orientation and depth — and how each is measured, accepted or corrected before grouting sets and before surfacing.
Civil tolerance is the permitted difference between the design and what is built in the civil works that carry the lights. A fixture can only be aligned and levelled as well as its base allows, so the base is measured as built against the design position, level and orientation, and is either accepted or rectified while that is still easy to do.
The checks come before the base is grouted or concreted in and again before surfacing or overlay buries the evidence. A base set too high can be a hazard, one set too low collects water and debris, and one out of position breaks the pattern spacing. Excavation is done under the airport’s permit-to-work, with existing cables and services located and protected before anything is dug.
- Set out. Survey the line and mark each position and level from the design drawings.
- Excavate. Dig to the design depth, locating and protecting existing cables and services first.
- Place. Set the base can or foundation at the design position and orientation.
- Measure. Check position, level and orientation against the design before it is fixed.
- Fix & cure. Grout or concrete the base, re-checking before it sets and again after.
- Record. Take as-built measurements before surfacing and after, and log any rectification.
Frequently Asked Questions
Q1What is civil tolerance in airfield ground lighting?
It is the permitted difference between the design and what is actually built in the civil works that carry the lights: base can position and level, spacing along the line, orientation, trench depth and foundation dimensions. Work inside the tolerance is accepted, and work outside it is corrected.
Q2Why does civil tolerance matter for a light?
A light can only be aligned and levelled as well as the base beneath it allows. A base set too high can be a hazard or be struck by vehicles, one set too low collects water and debris, and a base out of position or rotated breaks the spacing and aiming of the pattern.
Q3What is usually given a tolerance?
Position across the line and spacing along it, level relative to the finished pavement or ground, orientation of the base or index mark, depth and cover of ducts and trenches, and foundation dimensions for elevated lights and signs. The design drawings and specification define each one.
Q4When should tolerance be checked?
Before the base is grouted or concreted in, so errors can still be corrected, and again before surfacing or overlay work buries the evidence. A check after the pavement is finished confirms the as-built condition for the record.
Q5What happens if something is outside tolerance?
It is rectified or referred to the designer and the airport for a decision, and the outcome is recorded. A small error corrected at the base stage is far cheaper than one found after the pavement is laid.
Q6What tolerance values apply?
Values come from the project specification, the design, the regulator, the applicable standard and the manufacturer's instructions. Always use the figures for your site rather than a generic number.
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