Elevated Stop Bar Fixture

An Elevated Stop Bar Fixture is a raised stop bar light fixture mounted on a frangible pole or base plate above the pavement surface, providing a highly visible red stop indication at runway holding positions. The elevated design offers excellent visibility from a distance and is ideal for grass or soft shoulders where inset fixtures are not practical, while the frangible coupling ensures aircraft safety on impact. These fixtures are typically installed in a row across the taxiway at the runway holding position, creating a continuous line of red lights that forms a clear visual stop barrier, visible to pilots from a significant distance.

The elevated stop bar fixture's purpose is the same hard stop-and-hold function performed by any stop bar, but delivered at locations where an inset fixture isn't a practical option — grass or soft shoulders where flush mounting can't be achieved — while still forming the same continuous, high-visibility red barrier that tells a pilot unambiguously not to proceed past a runway holding position. Because a stop bar's entire safety function depends on it being unmistakably visible from a distance, its elevated position and frangible mounting let it deliver that visibility in exactly the ground conditions where a flush fixture would either be impossible to install correctly or prone to drainage and load-bearing problems, without compromising the breakaway safety behaviour required this close to an active runway.

Elevated stop bar fixtures are installed at runway holding positions on taxiways where elevated mounting is preferred or required. They are used on:

• Grass or soft shoulder taxiways where inset fixtures are not practical
• Precision approach runways (CAT II and III) where high visibility is required
• Busy airports with high traffic volumes where clear visual cues are essential
• Runway holding positions at the intersection of taxiways and runways
• Low visibility operations where enhanced visibility is critical
• Military airfields requiring robust and highly visible fixtures

Fixtures are set out in a row across the full taxiway width at the runway holding position, on a line perpendicular to the taxiway centreline, spaced to match the airport's stop bar lighting scheme so the completed row forms a single, unbroken red barrier. Each unit mounts on a frangible pole or base plate set into the shoulder or grass strip alongside the paved surface, with the pole height and frangible coupling matched to the same breakaway standards used for other elevated AGL fixtures at that location. Power and control cabling for the row is fed from the stop bar's own switchable circuit, kept independent from the general taxiway edge lighting so the bar can be illuminated or extinguished under direct ATC or ALCMS control without affecting other taxiway lighting. Where the row sits close to an active runway, mounting positions and pole heights are checked against the runway's obstacle-limitation surfaces to confirm the elevated fixtures don't themselves become an obstruction.

Elevated stop bar fixtures operate as an integral part of the runway safety system with a raised, highly visible design:

• Power: Powered from the constant current series circuit via an isolating transformer buried near the fixture (typically 45W – 65W).
• Light Source: Utilizes red LED arrays or red-filtered halogen lamps. The red colour provides a clear stop indication that is universally recognized by pilots.
• Beam Pattern: Projects a uni-directional beam pattern towards approaching aircraft, ensuring the red light is visible only to pilots facing the stop bar.
• Mounting: Mounted on a frangible pole or base plate approximately 300-500mm above ground level, with a breakaway design to minimize aircraft damage on impact.
• Control: Controlled by the ATC or ALCMS via the stop bar control module, with illumination indicating that the runway is occupied and it is unsafe to proceed.

Elevated stop bar fixtures are controlled as a single switched row rather than as individual lights. ATC or the ALCMS commands the stop bar on or off through a dedicated stop bar control module, which switches the row's circuit as one segment — on interlocked installations, this module also enforces that the stop bar cannot be lit at the same moment the taxiway centreline lights leading through the holding position are energised, so the two indications can never contradict each other.

Because the row is switched as a unit, a fault is reported at the level of the stop bar circuit rather than pinned to one fixture in the row without further testing — the same loop-level fault logic used elsewhere in AGL series circuits.

The fixture body is a die-cast aluminium alloy housing, machined and anodised or powder-coated to resist de-icing fluid, fuel spillage, and UV exposure over its exposed life. The red lens or filter is fitted over the light source and gasket-sealed to the housing with an O-ring or silicone seal, giving an IP66/IP67-rated enclosure against moisture and dust. The fixture bolts to a frangible coupling — a fitting engineered to shear cleanly on aircraft impact — which in turn seats on a base can set into the ground alongside the taxiway; the raised height and mounting geometry are chosen so the row of fixtures reads as a continuous line to an approaching pilot without presenting a hazard to aircraft or ground vehicles. Internal wiring terminates at L-823-style connectors that mate to the secondary leads of a nearby isolating transformer, with stainless-steel fasteners used throughout and a drainage provision in the base can to keep water from pooling around the transformer and cable entries.