What is CAT I approach lighting?

It is the approach lighting provided for Category I precision approaches, the least demanding ILS category. ICAO defines a Category I approach as one flown to a decision height of not less than 60 m (200 ft) with visibility of not less than 800 m or an RVR of not less than 550 m. The lights give the pilot a lead-in and alignment picture at that decision point.

A row of white lights on the extended runway centreline, 30 m apart, running 900 m back from the threshold wherever possible, with a single crossbar 30 m long at 300 m from the threshold. It has no red side rows, which is the main layout difference from the Category II and III system.

The FAA standard is MALSR. It is 2,400 ft long, with seven five-light bars out to 1,400 ft, a 1,000-ft crossbar and five RAIL flashers at 200-ft spacing from 1,600 to 2,400 ft. ALSF-1 is a legacy high-intensity system 2,400 to 3,000 ft long with centreline barrettes every 100 ft, a 1,000-ft bar, red pre-threshold and terminating bars, and sequenced flashers; it is defined in UFC 3-535-01 but is not listed in the current FAA installation order, JO 6850.2C. SSALR is used the same way as MALSR when Category I conditions exist on a Category II runway with a dual-mode ALSF-2/SSALR installation, and the FAA does not normally install it as a new stand-alone system.

Category II and III add red side rows and extra crossbars close to the threshold so the pilot has roll and distance-to-go cues at a lower decision height. In the ICAO system the side rows run 270 m from the threshold with crossbars at 150 m and 300 m. In the FAA system, ALSF-2 adds red side rows and a 500-ft bar to the ALSF-1 pattern and replaces the red pre-threshold and terminating bars of ALSF-1 with white lights.

At the decision point the pilot must acquire visual references before continuing. The approach lights are one of those references, and the lighting provided also feeds the visibility minimums on the approved procedure. Under the FAA rule for operating below DA/DH, a pilot may not descend below 100 ft above the touchdown zone using only the approach lights unless the red terminating bars or red side row bars are also visible.

No. ICAO and FAA use different dimensions and different systems, and the minimums come from the approved procedure for each runway. Use the published procedure and the aerodrome documents, not the system name, to find the minimums.

Treat the circuit as live until it is isolated, locked out and proved dead under the permit-to-work. The structures are elevated and stand in the runway protection area, so access and aircraft-movement controls apply. Where flashers are fitted (MALSR, ALSF-1) they are capacitor-discharge units, so discharge them as the manufacturer instructs before opening a head or cabinet.