Keeping navaids on air: availability, MTBF and MTTR for CNS engineering

Pilots and controllers rarely think about a VOR, an ILS localiser or a surveillance radar until it fails. For the CNS engineers who maintain them, availability is the only measure that counts. ICAO Annex 10 and its attachments discuss the reliability and availability expected of radio navigation aids, and most air navigation service providers set availability targets for each system class.

Setting a target is the easy part. Proving it is achieved, month after month, depends on maintenance data that is complete and trustworthy.

The three numbers that matter

All three are calculated from the same raw material: an accurate log of every outage, its start and end times, its cause and the work done to restore it.

Where the data usually breaks down

When outage records live in logbooks and spreadsheets at each station, the figures are only as good as the last person who transcribed them. Planned maintenance is mixed with faults, short outages go unrecorded and nobody can say with confidence why one site performs worse than another.

From station board to regulator report

SkyALITE CMMS connects the whole chain. Live station boards show each system, its standby and its status. A fault report becomes a work order, the work order records the restoration, and planned maintenance programmes run alongside, even offline at remote sites. Availability, MTBF and MTTR are then calculated directly from those records and are ready for management review or the regulator in a single report.