Elevated Runway Edge Light

An Elevated Runway Edge Light is a visual aid mounted on a small pole or pedestal above the runway surface (typically 300–500 mm high). It is the standard configuration for runways where the shoulder is soft (grass or gravel) or where a raised light offers the best optical performance. The fixture includes a frangible coupling that shears on impact, reducing the risk of damage to an aircraft that veers off the runway. Elevated lights are used on both precision and non-precision runways, with white or yellow (last 600 m / 2,000 ft) beam outputs.

The elevated configuration exists because raising the light head above grade generally gives the best possible optical performance for edge delineation, projecting a cleaner, more visible beam to an approaching or departing pilot than a flush fixture can achieve, and it is the default choice wherever the shoulder surface allows it. This benefit only holds where an aircraft veering off the paved surface won't be put at greater risk by striking the fixture, which is why the elevated light is fitted with a frangible coupling engineered to shear at a controlled, predetermined force: the design deliberately trades fixture survivability for aircraft safety in an off-runway excursion. Consequently, the elevated light's role is to be used wherever soft shoulders (grass, gravel) or unconstrained ground clearance make its superior optical output and frangible safety behaviour the right combination, reserving the inset alternative for surfaces where an elevated stem would itself be the hazard.

Installed on the runway shoulders, typically 1–3 metres outside the paved edge, at regular intervals (60 m / 200 ft for CAT I and above, up to 100 m / 300 ft for non-precision). Used on all airfields with grass, gravel, or compacted soil shoulders where an inset fixture is not feasible. Also common on taxiway edges and as standalone approach lighting support structures.

Fixtures are set out along both runway edges at the design spacing, positioned on the shoulder just outside the paved surface and clear of the graded runway strip's load-bearing requirements. Each stem mounts on a frangible coupling atop an L-867 base can set flush with grade, with overall fitting height kept within the obstacle-limitation surface for the runway category so the raised head never intrudes on the clearance envelope. The base can is fed by armoured cable run in a trench back to the isolating transformer pit, with the transformer housed in its own secondary base can adjacent to the fixture to keep the series-circuit joint clear of standing water. Setting-out is tied to the runway centreline survey so the edge line stays parallel and true along the full runway length, and elevated fixtures are typically substituted with inset units within the runway end safety area, blast pads, and other zones where a raised obstacle cannot be tolerated.

Each elevated light is powered from the series circuit via an isolating transformer buried near the fixture. The lamp or LED module projects light through a precision prism and lens assembly to create the required beam pattern (symmetric or asymmetric, depending on installation orientation). The intensity is controlled by the CCR's current steps. The frangible coupling is designed to break at a predetermined shear force (typically 250–450 kg), allowing the light head to detach cleanly without causing significant damage to an aircraft's wing or engine.

Elevated runway edge lights are not individually addressable — control is exercised at the loop level through the constant current series circuit. An Airfield Lighting Control and Monitoring System (ALCMS), operated by the tower or an automated visibility-linked routine, selects the required brightness step based on prevailing RVR, ATC instruction, or (at smaller aerodromes) pilot-controlled lighting input. This command is passed to the CCR, which regulates the entire loop to the corresponding fixed current (one of 5 steps between 2.8A and 6.6A). Every fixture on that loop, via its own isolating transformer, draws from the same current and therefore burns at the same intensity simultaneously — there is no way to dim or brighten a single fixture independently of the rest of the circuit. Fault detection is likewise loop-based: the CCR continuously monitors loop voltage against the commanded current, and a voltage rise at constant current signals increased circuit impedance, typically an open-circuit lamp or a failed isolating transformer, which is reported to the ALCMS as a loop fault rather than pinpointed to an exact fixture without further sectionalised testing. Because the elevated fitting sits on a frangible coupling, a sheared coupling looks electrically identical to any other open-circuit fault on the loop — the ALCMS reports it the same way, and only a field inspection confirms whether the cause was impact damage or a failed component.

The fixture head is a die-cast aluminium alloy housing, anodised or powder-coated for corrosion resistance, mounted atop a short stem or pedestal (typically 300–500 mm) that raises the optics clear of grass or gravel shoulders for a cleaner beam path. The optical assembly sits under a borosilicate glass or high-strength polycarbonate prism, gasket-sealed to the housing with an O-ring or silicone seal for an IP67/IP68 rating against rain, dust, and fuel exposure. The stem attaches to the base through a frangible coupling, an aluminium or composite fitting engineered to shear cleanly at a defined load if struck by an aircraft, wheel, or ground vehicle, minimising damage to both the aircraft and the fixture's electrical connections below the break point. The coupling in turn seats on an L-867 base can set flush with the surrounding grade. Internal wiring terminates at L-823 primary connectors, sealed for direct burial and continuous immersion, mating to the isolating transformer's secondary in an adjacent base can, with stainless-steel fasteners used throughout and a drainage provision in the base can to keep the connector joint clear of standing water.