Side Row Bars

Side Row Bars are a critical component of precision approach lighting systems. They consist of rows of lights installed on both sides of the approach centreline, typically at fixed distances from the runway threshold. These lights provide lateral guidance to pilots during final approach by defining the approach corridor and helping pilots maintain proper alignment with the runway centreline.

Side Row Bars are configured as part of the ALSF-1 and ALSF-2 precision approach lighting systems. They occupy the inner 1,000 ft of the system nearest the runway — installed as two rows of red lights, one on each side of the extended centreline, forming a "runway-shaped box" between the threshold and the 1,000 ft decision (roll) bar. The lights are steady-burning red, at an intensity well below the white centreline/flasher stations, and give the pilot a visual reference confirming the aircraft is still in the approach light system and short of the runway threshold — the same red reference required to descend below 100 ft AGL under 14 CFR 91.175 when only the approach lights are in sight.

Side Row Bars exist to define the outer boundary of the approach corridor from a distance, giving the pilot a clear sense of the safe lateral envelope to stay within, in addition to the fine centreline tracking that the barrettes and centreline lights provide. Because they sit on both sides of the approach path rather than on it, they let a pilot judge overall corridor width and position within it holistically, functioning like a visual "gate" the aircraft flies through, rather than requiring the pilot to reconstruct that boundary purely from a single centreline reference. This dual-reference approach — centreline for fine tracking, side row bars for the broader corridor — is precisely why full precision systems combine both rather than relying on either alone.

Side Row Bars are a standard component of precision approach lighting systems and are used on:

• CAT I precision approach runways (ALSF-1 configuration)
• CAT II/III precision approach runways (ALSF-2 configuration)
• Runways with low visibility operations (RVR below 800m)
• Military airfields requiring precision approach capability
• Major international airports with high traffic volumes
• Runways with complex approach paths requiring enhanced lateral guidance

Side row bars are erected on their own poles flanking the centreline barrette piers, offset laterally at the standard approach lighting width either side of the extended runway centreline, with pole spacing matching the centreline barrette interval so each side row light sits level with its corresponding centreline barrette. Poles share the same foundation line and, on approaches over water or uneven terrain, the same raised platform or bridge structure as the centreline piers. Cabling runs along the side row pole line back to the approach lighting control cabinet, with an isolating transformer at each pole base, and the full layout is set out from the same ILS/runway centreline survey used for the centreline barrettes.

Side Row Bars operate as an integral part of the approach lighting system:

• Configuration: Side Row Bars are installed as two rows of lights, one on each side of the approach centreline, confined to the inner 1,000 ft of the approach lighting system nearest the runway threshold — not spaced out beyond it. Each row consists of light stations at longitudinal intervals matching the centreline light stations (typically every 100 ft), with 3 lights per side at each station.
• Lighting: The lights are steady-burning red, distinguishing this final 1,000 ft "box" from the white high-intensity centreline lights and sequenced flashers that terminate at the 1,000 ft decision (roll) bar. Side Row Bars are not sequenced or flashed.
• Guidance: The visual "gates" created by the side row bars provide lateral guidance to the pilot, defining the approach corridor. If the aircraft is off-centreline, the pilot will see the bars asymmetrically, indicating the need to correct the approach path.
• Integration: Side Row Bars are integrated with other approach lighting components — centreline barrettes, crossbar lights, sequenced flashing lights — to provide a comprehensive visual guidance system for precision approaches.

Side Row Bars are not individually addressable — they are wired into the same constant current series circuit as the rest of the approach lighting system (ALS) they belong to, whether that is a CAT I configuration, SSALR, MALSR, or a full CAT II/III system. An Airfield Lighting Control and Monitoring System (ALCMS), driven by RVR category selection or ATC instruction, sets the CCR brightness step for that circuit. Because side row bars typically share a loop (or a dedicated sub-circuit fed from the same regulator bank) with crossbars and centreline barrettes, every bar switches on and dims together with the rest of the ALS — there is no independent control of a single bar or pair. Each fixture draws its supply through its own isolating transformer, tapping a fixed secondary current from the loop. Fault detection remains loop-based: the CCR watches loop voltage against the commanded current, and a voltage rise at constant current is reported to the ALCMS as a circuit fault rather than pinpointed to an individual bar.

Side row bar fixtures use the same die-cast aluminium housing family as other high-intensity approach lights, anodised or powder-coated for corrosion resistance and fitted with a hardened glass or polycarbonate prism to shape and focus the beam toward the approach path. Because each bar groups several lights together at a fixed cross-bar spacing, individual fixtures are mounted on a common structural bar or on closely spaced individual poles set to a matched height and aim, with each unit bolted to its own frangible coupling and L-867 base can so that an aircraft impact shears the fixture cleanly without damaging the bar's neighbouring units. The optical assembly is gasket-sealed with an O-ring to achieve an IP67/IP68 rating, and internal wiring from each light in the bar terminates at sealed L-823 connectors feeding its own isolating transformer, keeping the bar's series-circuit wiring independent per fixture for fault isolation. Precise alignment across all lights in a bar is critical, since side row bars work as a lateral pair to define the approach corridor, so mounting stakes and base cans are set and levelled to a common reference during installation. Stainless-steel fasteners are used throughout for durability in the exposed approach lighting environment.