Approach Light Barrette

An Approach Light Barrette is a short row of high‑intensity lights installed perpendicular to the approach centreline, typically consisting of 3 to 5 lights spaced 1–2 metres apart, forming a distinctive "bar" across the approach path. These barrettes are placed at fixed distances from the runway threshold (e.g., 300 ft, 600 ft, 900 ft, 1,200 ft, etc.) as part of the approach lighting system (ALSF‑1, ALSF‑2, MALSF, and other configurations). They provide pilots with a series of bright visual reference points that help maintain precise lateral alignment and judge distance‑to‑go during the final approach segment.

Approach light barrettes are a fundamental component of both precision and medium‑intensity approach lighting systems. They work in conjunction with centreline barrettes, crossbar lights, side row bars, and sequenced flashing lights (SFL) to create a comprehensive visual reference for the pilot, particularly in low visibility (CAT I/II/III) operations where accurate glide‑path and centreline tracking are critical.

The approach light barrette's purpose is essentially the same distance-and-alignment guidance the approach crossbar provides, applied more densely and closer to the runway to give a pilot a finer-grained series of visual checkpoints as the aircraft gets nearer to the threshold. Because barrettes are spaced more tightly than crossbars, their cumulative effect is a continuous, closely-spaced sequence of lateral reference bars that lets a pilot track alignment and closing distance with more precision exactly where the margin for error is smallest — in the final few hundred metres before touchdown.

Approach light barrettes are deployed on precision and non‑precision approach runways and are used in:

• CAT I precision approach runways (ALSF‑1) – providing essential distance and lateral guidance for approaches with 200 ft decision height.
• CAT II and III precision approach runways (ALSF‑2) – critical for low‑visibility operations with decision heights as low as 100 ft or less.
• Medium‑intensity approach lighting systems (MALSF, MALSR) – providing enhanced visual cues for non‑precision runways with higher traffic volumes.
• Runways with low‑visibility operations (RVR below 800 m) – ensuring pilots have continuous distance and alignment cues.
• Major international airports – where high traffic volumes and adverse weather demand reliable approach guidance.
• Military airfields – requiring all‑weather precision approach capability.

Barrettes are mounted on the approach lighting structures at the stations set out along the extended runway centreline, spaced at the intervals specified for the ALS configuration in use, with each barrette's row of light units running perpendicular to the approach path. The barrette sits on a frangible support at the design height, individually levelled and aimed during commissioning so the row reads as a single bar of light from the approach. Secondary cabling from the nearest approach light junction box is run up the structure to the barrette, and its distance from the threshold is set out from the approach lighting survey so the full string of barrettes provides a continuous, evenly spaced line of guidance.

Approach light barrettes function as a series of visual reference points along the approach path:

• Configuration: Each barrette is a short row of 3‑5 lights, typically spaced 1–2 m apart, installed perpendicular to the approach centreline. Multiple barrettes are placed at specific distances from the threshold (e.g., 300 ft, 600 ft, 900 ft, 1,200 ft, 1,500 ft, etc.) to provide a regular visual pattern along the approach path.
• Lighting: The lights are high‑intensity white, steady‑burning or flashing, with intensity controlled by the CCR (5‑step). In some systems, barrettes may flash in sequence to create a "running" effect that guides the pilot toward the runway.
• Distance Reference: As the aircraft descends, the pilot sees the barrettes as short horizontal bars. The spacing between barrettes provides distance‑to‑go information, helping the pilot judge approach progress and descent rate.
• Lateral Guidance: If the aircraft is off‑centreline, the barrettes will appear asymmetrical, indicating the need for lateral correction. The perpendicular orientation of the barrettes provides a clear reference for maintaining centreline alignment.
• Integration: Approach light barrettes are integrated with centreline lights, crossbar lights, side row bars, and sequenced flashing lights (SFL) to form a comprehensive visual approach system. They are typically positioned at regular intervals along the approach lighting structure.

Barrettes are controlled at the loop level, exactly like the crossbars, side rows, and sequenced flashers they share the approach lighting circuit with — none of these fixture types can be switched or dimmed independently of the others once they sit on the same loop. An ALCMS, acting on RVR data, ATC instruction, or pilot-controlled lighting, selects the required intensity step and hands it to the approach lighting CCR, which drives the whole loop to that fixed current. Because barrette stations are more numerous and more closely spaced than crossbars (typically every 30 m, extending out to 900 m from the threshold per ICAO CAT II/III, or up to 3,000 ft/~915 m in FAA ALSF configurations), a single loop often carries a longer run of isolating transformers, which is one reason approach circuits are frequently split into inner and outer loop sections so a fault or maintenance isolation on one section doesn't blank the entire approach light array. Fault reporting stays loop-based regardless: the CCR flags an open circuit as a voltage-rise event on its loop, and pinpointing which barrette station failed still requires a field check rather than a discrete signal from any single unit.

Each barrette light is a self-contained high-intensity fixture — an LED array or 45W/65W/100W halogen lamp behind a precision optical prism, housed in a die-cast aluminium body that is anodised or powder-coated against jet fuel, de-icing fluid, and UV exposure. Elevated barrettes mount each fixture on a frangible coupling and pole seated in an L-867 base can, so an individual light shears cleanly off on impact without disturbing its neighbours; flush-mounted barrettes instead seat each fixture in an L-868 base can rated for aircraft wheel loading. What makes a barrette a single component rather than several unrelated lights is the shared civil layout: 3–5 fixtures are set 1–2 metres apart in a fixed row, wired back to individual isolating transformers of matched wattage, and aligned so their beams present as one continuous bar to an approaching aircraft. Gasket-sealed top caps and O-ring seals on each fixture give the assembly its IP67/IP68 rating, and sealed L-823 splice connectors carry the series circuit between fixtures and back to the primary cable.