Runway End Identifier Light (REIL)

A Runway End Identifier Light (REIL) is a pair of high-intensity flashing lights installed on either side of the runway threshold. These lights produce synchronized or alternating flashes (typically white) that are visible from a great distance, providing pilots with an unmistakable visual identification of the runway end. REIL systems are particularly valuable for non-precision runways and airports located in areas with significant background lighting where traditional steady-burning threshold lights might be less conspicuous.

REIL exists to solve a specific problem that steady-burning threshold lights don't fully address: making the runway threshold instantly conspicuous against background clutter, whether that's the ambient city lighting surrounding many airports or the general absence of surrounding visual references at an unlit rural strip. A flashing high-intensity light is inherently more attention-grabbing to the human eye than a steady one at the same distance, which is precisely why REIL is used to positively identify the threshold from far out on approach, before the pilot is close enough to resolve the steady threshold and edge lighting in detail. Its purpose is therefore concentrated on the early, long-range phase of a non-precision approach, where confirming the correct runway and threshold as early as possible reduces the risk of confusion with nearby lighting, roads, or another runway.

Installed at the threshold of runways requiring enhanced identification, particularly:

• Non-precision runways where additional visual cues are beneficial
• Runways in urban areas with significant background light clutter
• Runways with difficult approach paths where runway acquisition is challenging
• Military airfields requiring rapid runway identification
• Remote or offshore airports where the runway needs to be distinguished from surrounding terrain

A pair of REIL units is installed symmetrically on either side of the runway threshold, roughly 10–15 m outward from the runway edge, positioned in line with the threshold lights so the flash is visible on the extended runway centreline from the approach. Each unit mounts on a frangible stem set in its own base can, fed by cable run in a trench or duct back to the REIL control unit, which houses the flash-tube power supply, synchronisation circuitry (for unidirectional systems), or independent flash control (for omnidirectional systems), together with any pilot-activated or ATC-controlled switching. The control unit is typically located in an equipment enclosure near the threshold, separate from the general runway lighting vault, since REIL is usually run on its own dedicated power supply rather than the runway series circuit. Placement keeps the units within the obstacle-limitation surface for the runway category, with omnidirectional units favoured where the runway serves varied approach directions.

Each REIL unit consists of a high-intensity light source (typically xenon flash tube or high-power LED array) with a parabolic reflector to project a concentrated beam. The two units are installed approximately 10-15 metres (30-50 feet) from the runway edge, aligned with the threshold. They flash in a synchronized or alternating pattern (typically 60-120 flashes per minute). The system is powered from the airfield electrical supply, with a dedicated controller that provides flash pattern control and intensity adjustment. Unlike most AGL fixtures, REIL systems are typically not powered from the series circuit but from a separate power source.

Unlike loop-controlled AGL fixtures, REIL is not addressed through the airfield series circuit at all — it runs off a dedicated supply with its own controller, so its control logic is a separate command chain rather than a branch of the CCR network. Activation typically comes from ATC or, at smaller aerodromes, pilot-controlled lighting (PCL) keyed from the aircraft radio; either input is decoded by the REIL controller, which generates the flash timing (60-120 flashes per minute), selects synchronized or alternating operation between the two units, and — on systems with adjustable output — sets flash intensity independently of any RVR-linked step table. Because each unit has its own flash-tube (or LED) drive circuit rather than sharing a single loop current, the two units can, and in alternating-mode systems must, be driven out of phase with each other. This also changes fault handling: the controller monitors each drive circuit separately, so a failed left or right unit is reported and isolated on its own, without darkening the other unit or being masked as a generic loop fault the way a CCR-driven fixture failure would be.

Each unit is a pole-mounted, elevated fixture with a die-cast aluminium alloy or high-impact polycarbonate housing, weatherproofed and UV-stabilised to withstand continuous outdoor exposure at the runway end. The xenon flash tube or LED array sits behind a clear, high-strength polycarbonate dome or lens, gasket-sealed to achieve an IP65/IP67 rating against wind-driven rain and dust. The mounting pole is typically a low-impact, frangible or break-away design so the fixture yields safely if struck, and the base is anchored on a concrete footing set back from the runway end per the applicable siting criteria. A weatherproof enclosure at the pole base or nearby houses the flash-tube power supply and controller circuitry, since REIL units run on a dedicated mains feed rather than the series circuit used by most other AGL fixtures, and are cabled back to that supply through sealed, direct-burial-rated connectors.