How does a serviceability result trigger maintenance?
A count only matters if it sets work in motion. Each result falls into one of three bands: within the objective, at the action level, or not met. Each band has its own response, from routine scheduling to telling airfield control straight away.
Entry 30 produces a serviceability result. This entry is about what the result sets in motion. The objective is what the preventive maintenance system is built to hold (Entry 26), so the response should start before the objective is breached, not after. The flow has three bands, and each has its own response, timing and notification.
1Three bands, three responses
| Band | Example: 60-light CAT II/III runway edge row | Response | Notify |
|---|---|---|---|
| Within objective | 0 to 1 out, none adjacent | Log it, repair at the next routine visit | No |
| Action level reached | 2 to 3 out, none adjacent | Raise a work order, restore soon | If the objective is at risk |
| Objective not met | 4 or more out, any adjacent pair, or a critical-light objective breached | Restore at once | Airfield control, straight away |
2The action level sits above the objective
At 95 per cent the objective allows three lights out of 60 (Entry 27). A row sitting on three has no margin: one more failure breaches it, and a second beside it breaks continuity of guidance (Entry 28). The action level is set higher up, for example two out, so the work starts while the objective is still met. It is not an ICAO figure: the objective comes from Annex 14, and the action level is the operator’s own choice in its maintenance plan.
3What can trigger the flow
| Trigger | Example | Band |
|---|---|---|
| Count reaches the action level | 2 of 60 edge lights out | Action level |
| Percentage below the objective | 4 of 60 out is 93 per cent, below 95 | Not met |
| Adjacent pair out | Two neighbouring lights, even if the percentage is met | Not met |
| Critical light affected | A stop bar with more than two lights out (RVR below 300 m) | Not met |
| Lit light below the 50% line | Intensity measurement shows a dim light | Recount, then re-band |
| A whole circuit down | Alternate lights out: no adjacent pair, but the percentage may fail | Check the percentage at once |
4Telling the right people
When an objective is not met or a critical light is affected, tell airfield control straight away, without waiting for the repair. What happens to operations is not the maintenance team’s call: restricting operations or using alternative procedures is a decision for the aerodrome operator and air traffic services (Entry 29). Where an outage will last, publication, for example by NOTAM, follows your State’s rules (Entry 30).
5Restore in the right order
Critical lights first, such as a stop bar or CAT II/III centreline, then any adjacent pair, restoring one light of the pair first. Where you cannot tell whether a gap lapses guidance, restore one of the pair first (Entry 28). If a whole circuit is down, find the circuit fault before replacing lamps one by one (see Lamp-Out Behaviour in a Series Circuit).
6Close out and learn
After each repair, recheck the count and the positions instead of assuming the result, and log the times the fault was found and restored. Then review the log for trends. A circuit or fixture type that keeps coming back points to a cause, such as water ingress, a bad connector or a power-supply problem, and that is handled through corrective and preventive maintenance rather than another lamp swap.
- Act at the action level, not at the limit
- Tell control straight away when the objective is not met
- Recheck count and positions after every repair
- Wait for the objective to be breached before planning work
- Judge a row by its percentage and ignore adjacency
- Leave a pair out until the next routine visit
Frequently Asked Questions
Q1What triggers maintenance from a serviceability result?
Any of four things: the count reaching the operator's action level, the percentage falling below the objective, an adjacent pair of unserviceable lights, or a critical light affected, such as a stop bar with more than two lights out. A lit light measured below 50 per cent of its specified intensity also counts as unserviceable and goes into the count.
Q2What is an action level and who sets it?
It is a level set above the objective so that work starts while the objective is still met. It is not an ICAO figure. The operator sets it in its own maintenance plan, for example two lights out on a row where the objective allows three. The objective itself comes from Annex 14, Volume I, Chapter 10.
Q3Why act before the objective is breached?
The objective is what the preventive maintenance system is built to hold, not a pass mark applied once. A row sitting exactly on its limit has no margin: one more failure breaches it, and a second failure beside it breaks continuity of guidance. Acting at the action level keeps that margin.
Q4When must airfield control be told?
Straight away when an objective is not met or a critical light is affected, without waiting for the repair. Restricting operations or using alternative procedures is a decision for the aerodrome operator and air traffic services, and publication of a long outage, for example by NOTAM, follows your State's rules.
Q5Which lights are restored first?
Critical lights first, then any adjacent pair, restoring one light of the pair first. Where you cannot tell whether a gap lapses guidance, restore one of the pair first. After each repair, recheck the count and the positions rather than assuming the result.
Q6What happens after the repair?
The count and positions are rechecked against the objective, the times the fault was found and restored are logged, and the result is closed out. The log is then reviewed for trends: the same circuit or fixture type failing again points to a cause, which is handled through preventive or corrective maintenance.
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