What is torque checking?
Confirming that the bolts holding a light fixture are tightened to the manufacturer’s value — firm enough to stay put and keep the seal tight, never so tight that something gives way.
Torque checking proves that the fasteners holding an airfield light in place are tightened to the value set by the manufacturer. Inset fixtures sit in the pavement, where wheel loads, vibration and thermal movement can gradually loosen bolts, and a fixture that works loose can move, lose its seal and let water into the fixture and base can.
The check is done with a calibrated torque wrench, tightening opposite bolts in turn in a cross pattern so the fixture seats evenly. Too little torque leaves the fixture loose; too much can strip threads, crush the seal or crack the flange. For that reason the data-sheet value for the exact model is the target, not a general rule of thumb.
- Prepare. Work under your permit-to-work (isolate the circuit if the fixture will be opened or removed), clean the fixture and flange, and find the torque value on the manufacturer’s data sheet.
- Inspect. Check bolts, washers, threads and the seal for damage or corrosion; replace anything worn or damaged with manufacturer-approved bolts, washers and seals.
- Set. Fit the correct socket and set the calibrated wrench to the specified value.
- Check. Apply the specified torque to each bolt in the cross-pattern sequence; a bolt that turns before the wrench clicks was below value. Re-tighten it, and any bolt on a fixture that was removed or replaced, in two or three steps up to the full value, then make a final pass at full value.
- Mark. Paint a torque stripe across each bolt and flange so later movement is easy to see.
- Record. Log the fixture, the value applied and any bolts found loose or replaced.
Frequently Asked Questions
Q1What is torque checking in airfield lighting maintenance?
Confirming with a calibrated torque wrench that the bolts and nuts holding a fixture, base cover or sign are tightened to the value the manufacturer specifies, and re-tightening any that have loosened.
Q2Why not just tighten the bolts as hard as possible?
Over-tightening can strip threads, crush the seal and crack a flange or lens ring. The aim is the specified clamping load, enough to hold the fixture and keep the seal compressed, not the maximum.
Q3Where does the correct torque value come from?
From the fixture or sign manufacturer's data sheet or installation instructions for that exact model, bolt size and any lubricant or thread compound. It is not a universal figure, so the manufacturer's value is the reference.
Q4Why tighten in a cross pattern?
Tightening opposite bolts in turn, in several steps, pulls the fixture down evenly. Tightening one bolt fully and then the next can tilt the flange and leave the seal pinched on one side.
Q5How often should torque be checked?
The interval is set by the aerodrome's maintenance programme and the manufacturer's guidance. It is commonly part of routine fixture inspection and is repeated after a fixture is removed, replaced or disturbed by pavement works.
Q6Does the torque wrench need to be calibrated?
Yes. A wrench that is out of calibration gives false confidence, so it is calibrated at the intervals set by the quality system and checked for damage before use.
Q7What if bolts are found loose?
Re-tighten them to the specified value in the cross-pattern sequence, then inspect the bolts, threads and seal for damage and check the fixture and base can for water ingress. Replace anything damaged, record the finding, and look at neighbouring fixtures, because a pattern of loose bolts can point to a cause such as vibration or pavement movement.
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