Elevated Approach Light

An Elevated Approach Light is a high‑intensity light fixture mounted on a frangible pole or support structure above the ground or pavement surface. Unlike inset (flush‑mounted) lights, elevated approach lights are raised above the surrounding terrain, making them suitable for approach lighting systems where snow accumulation, uneven ground, or frequent maintenance access are considerations. They are typically used as part of approach lighting systems (ALSF‑1, ALSF‑2, MALSF, etc.) to provide centreline, crossbar, or barrette guidance, with the light beam directed towards approaching aircraft. The frangible mounting ensures the fixture breaks away safely on impact, minimising damage to aircraft.

Elevated approach lights are a standard component of many approach lighting configurations, particularly at airports in cold climates where snow removal is a significant operational factor. They offer the same photometric performance as their inset counterparts but with improved visibility in snow and easier access for maintenance and lamp replacement.

The elevated approach light's purpose is to deliver the same guidance function as an inset fixture while solving the opposite problem: staying visible and accessible in conditions where a flush-mounted light would be buried under snow or difficult to reach for lamp replacement and maintenance. Its raised position keeps the beam clear of snow accumulation and uneven ground that could otherwise obscure or distort an inset fixture's output, which is why it is the preferred choice at airports in cold climates, while its frangible mounting ensures that this improved visibility and serviceability doesn't come at the cost of aircraft safety if the fixture is struck.

Elevated approach lights are deployed on precision and non‑precision approach runways and are used in:

• CAT I precision approach runways (ALSF‑1) – providing centreline and crossbar 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.
• Airports in cold climates – where snow accumulation makes inset fixtures difficult to maintain and clear.
• Runways with uneven terrain – where flush mounting is not feasible due to ground conditions.
• Military airfields – requiring rugged and easily maintainable lighting solutions.
• Temporary or expeditionary airfields – where rapid deployment and relocation are required.

Elevated approach lights are mounted on a frangible support atop the approach light structure at their designated station along the extended runway centreline, at the height and offset called for by the ALS configuration in use. Each fixture is individually aimed and levelled during commissioning so its beam projects correctly toward the approach path, and cabling is run up the structure from a nearby junction box with enough slack near the coupling to allow a clean frangible break without immediately severing the conductor. Elevated mounting is generally chosen over inset fixtures where the terrain beneath the approach lighting array is unpaved, uneven, or subject to heavy snow, since a flush-mounted fixture would be difficult to install or maintain on that ground.

Elevated approach lights operate on the same principles as other approach lighting components, with the added benefit of a raised mounting:

• Configuration: Each elevated approach light is mounted on a frangible pole or support structure, typically 0.3–1 m above ground level. The fixture is oriented to direct its beam towards approaching aircraft, with the beam pattern tailored to the specific application (centreline, crossbar, barrette, etc.).
• Lighting: The lights are high‑intensity white, steady‑burning or flashing, with intensity controlled by the CCR (5‑step). The elevated position improves visibility in snow and allows for a more consistent beam pattern unaffected by pavement surface conditions.
• Guidance: The lights provide lateral and distance guidance to pilots, helping maintain centreline alignment and glide‑slope tracking. The elevated position makes them more conspicuous, especially in snow or rain.
• Frangible Design: The mounting pole is designed to break away on impact, minimising damage to aircraft. The fixture is typically connected to the pole via a frangible coupling that shears under a specified load.
• Maintenance: Elevated lights are easier to access for maintenance, lamp replacement, and cleaning compared to inset fixtures, reducing downtime and operational disruption.
• Integration: Elevated approach lights are integrated with other approach lighting components to form a complete visual approach system, with the same electrical and control interfaces as inset fixtures.

Elevated approach 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 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 fixture sits on a frangible pole, 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 body is a die-cast aluminium housing, machined and anodised or powder-coated for corrosion resistance, mounted atop a frangible pole or bracket that is engineered to shear cleanly under aircraft impact loads. The optical assembly — a high-intensity lamp or LED array behind a borosilicate glass or polycarbonate prism — sits under a gasket-sealed top cap achieving an IP66/IP67 rating against rain, dust, and de-icing fluid exposure. The frangible pole seats on a base can (L-867 or approach-light-stand equivalent) set into the ground or approach light bridge structure, with the pole height and aim adjustable during installation to achieve the correct beam elevation and azimuth for the approach path. Internal wiring runs down the pole to sealed L-823 primary connectors at the base, mating to the secondary leads of a nearby isolating transformer housed in its own base can. Stainless-steel fasteners, corrosion-resistant hardware, and a drainage provision in the base can are standard, given the fixture's typically unpaved and exposed approach-area location.