Simple Approach Lighting System (SALS)

The Simple Approach Lighting System (SALS) is a basic approach lighting system designed for non‑precision runways. It consists of a single row of steady‑burning white lights extending from the runway threshold into the approach area, typically for a distance of 420 metres under the ICAO Simple Approach Lighting System standard (centreline at 60m intervals, with a single crossbar at 300m). Note: "SALS" is primarily an ICAO/historical term; the closest current FAA counterpart is the SSALS (Simplified Short Approach Lighting System), a 427m/1,400 ft truncated ALSF‑2 configuration — the two are not directly interchangeable and site documentation should confirm which standard actually applies. Unlike more complex systems such as ALSF‑1 or MALSR, SALS does not include sequenced flashing lights or crossbar lights. It provides pilots with a basic visual reference for aligning with the runway centreline during final approach, making it a practical and economical solution for smaller airports, regional airfields, and general aviation facilities.

SALS exists to give smaller airports, regional airfields, and general aviation facilities a functional visual centreline reference for night and marginal-weather approaches, at a fraction of the cost and infrastructure demand of a precision system. Its deliberate simplicity — a single row of steady-burning lights with no crossbars or sequenced flashing — reflects a purpose scoped specifically to basic alignment rather than the fine distance, depth, and directional cues that ALSF-class systems provide, which are unnecessary at fields without the traffic volume or low-visibility operations that would justify them. Its purpose is therefore about accessibility: providing a meaningful safety improvement over having no approach lighting at all, calibrated to what smaller facilities can practically support.

SALS systems are installed at airports that support non‑precision approaches. They are typically used on:

• Non‑precision runways with VOR, NDB, or GPS approaches
• Regional and general aviation airports with lower traffic volumes
• Smaller airfields with budget constraints for AGL infrastructure
• Military airfields with basic approach requirements
• Runways with visual approaches that benefit from enhanced night guidance
• Airports transitioning to higher categories where SALS serves as a baseline

Fixtures are mounted on lightweight frangible stands set out along the extended runway centreline at 60 m spacing, running from the threshold out to 420 m, with a single crossbar at the 300 m point. With no flashing circuit or crossbar structures to coordinate, the array is wired as a single steady-burning series circuit, with cable run in duct from each stand back to the regulator. Stand loads are modest, so elevated piers are needed only where the extended centreline crosses a road, ditch, or similar minor obstacle. Setting-out is tied to the runway centreline extended and threshold survey.

The SALS system operates on a simple principle: a row of lights provides a visual centreline reference for the pilot:

• Single Row of Lights: A row of steady‑burning white lights (typically 30m to 60m spacing) extends from the runway threshold out into the approach area, providing a visual centreline reference.
• Length: The system typically extends 420 metres from the threshold under the ICAO standard, with a single crossbar at 300m. The nearest FAA equivalent, SSALS, extends 427 metres (1,400 ft) — the two standards use different fixture spacing and are not identical.
• Lateral Guidance: The row of lights helps the pilot align the aircraft with the runway centreline during the final approach segment.
• Distance Reference: The spacing of the lights provides a rough distance reference, helping the pilot judge the approach path.
• Intensity Control: The lights are typically controlled by a CCR with intensity steps (usually 3‑step or 5‑step), allowing the ATC to adjust brightness for visibility conditions.
• Simplicity: The system has no flashing lights, crossbars, or complex sequencing, making it simple to install, operate, and maintain.

SALS runs on a single series circuit loop with no sequencer stage — every fixture along the 420 m row (plus its single 300m crossbar) is wired into the same loop and switches and dims together as one system, making it the most straightforward control chain in the approach lighting family. An Airfield Lighting Control and Monitoring System (ALCMS), operated by the tower or an automated visibility-linked routine, selects the required brightness step; this command is passed to the CCR, which regulates the whole row to the corresponding fixed current. Every fixture, via its own isolating transformer, draws from the same current and therefore burns at the same intensity simultaneously — there is no way to command an individual light, or a section of the row, independently of the rest. Fault detection follows the same loop-based principle used across the AGL series circuit family: 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, reported to the ALCMS as a loop fault rather than pinpointed to an exact fixture without further sectionalised testing.

The entire system is one steady-burning row on a single series circuit. ICAO's SALS (420m, 60m spacing, single 300m crossbar) and the FAA's nearest counterpart, SSALS (427m, no crossbar), are different configurations of the same basic idea, not the same fixture carried a different distance — verify which standard actually applies to a given site rather than treating the figures as interchangeable. There's nothing sequenced in either, which is what keeps this family cheap to install and maintain relative to ALSF-type systems.

Each fixture is a die-cast aluminium housing containing an LED array or 45–100W halogen lamp behind a toughened lens, gasket-sealed with an O-ring or silicone seal to achieve an IP67/IP68 rating, mounted on a frangible aluminium or composite stand bolted to a shallow concrete footing or ground screw anchor. With no flasher stage or crossbar structures to build, the array consists of identical stands at uniform spacing, all wired into a single steady-burning series circuit. Internal wiring terminates at L-823 primary connectors sealed for direct burial, which mate to the secondary leads of the isolating transformer housed at the base of each stand, with cable run in duct back to the regulator. Stainless-steel fasteners and corrosion-resistant finishes are used throughout to withstand continuous outdoor exposure over unprepared approach terrain.