Taxiway Lead-off Light

A Taxiway Lead-off Light is a specialized taxiway guidance light that provides directional guidance to pilots transitioning from the runway onto the taxiway after landing. These lights are typically installed in pairs on either side of the taxiway centreline at the exit point from the runway, forming a visual funnel that guides the pilot safely off the runway and onto the correct taxiway route. Lead-off lights are essential for ensuring efficient runway occupancy and safe aircraft movement during the post-landing phase.

Lead-off lights exist for the specific moment right after touchdown when a pilot's priority shifts from decelerating on the runway to committing to the correct exit — a transition that has to happen quickly, often at speed, and without ambiguity about which direction the taxiway curves away from the runway. The paired, funnel-shaped arrangement gives an instant, unmistakable visual cue for the turn direction before the pilot's eyes have even fully registered the taxiway centreline itself.

Getting this transition right is also an airfield capacity issue: an aircraft that lingers on the runway while the crew works out where the exit goes delays the next arrival or departure behind it. By making the direction of travel obvious from the moment the aircraft reaches the exit point, lead-off lights help keep runway occupancy time short and traffic flowing safely behind the exiting aircraft.

Taxiway lead-off lights are installed at runway exits where taxiways connect to the runway. They are used on:

• Precision approach runways (CAT II and III) where efficient runway exit is critical
• Busy airports with high traffic volumes requiring rapid runway clearance
• Rapid exit taxiways where high-speed exits are required
• Complex taxiway layouts where accurate guidance is essential
• Low visibility operations where visual guidance is critical

Fixtures are set out along the curved exit path from the runway centreline to the parallel taxiway centreline, using the standard inset base can recessed into the pavement at each survey point through the turn, with spacing following the exit curve's geometry rather than a fixed interval. Because these fixtures sit within the runway strip and exit curve where colour must change progressively from runway yellow to taxiway green, they are wired on the exit's own lighting circuit (kept separate from the parent runway centreline circuit) so the colour transition can be switched independently of the runway lights; cabling runs in duct beneath the pavement back to the isolating transformers and exit lighting controller, with setting-out tied to the runway exit's geometric design survey.

Taxiway lead-off lights operate as part of the taxiway and runway guidance system:

• Installation: Lead-off lights are installed in pairs on either side of the taxiway centreline at the runway exit point, typically at 15-30 metre intervals from the runway edge to the taxiway.
• Lighting: The lights are typically green or yellow, providing directional guidance to the pilot. The lights may be steady burning or flashing, depending on the application.
• Guidance: The visual funnel created by the paired lights guides the pilot to safely exit the runway and enter the taxiway.
• Integration: Lead-off lights are integrated with taxiway centreline lights, edge lights, and other taxiway guidance systems.

Taxiway lead-off lights are wired into the same type of constant current series circuit as the runway lighting they connect to and, like runway edge lights, are not individually addressable. The tower or an automated visibility routine — at advanced aerodromes, an A-SMGCS route-lighting controller deciding which taxiway segment should be lit for a given routing — issues the on/off or brightness-step command for the exit circuit. This command reaches the CCR, which regulates the entire loop to a single fixed current; every fixture on that loop, including both members of a lead-off pair, draws through its own isolating transformer and therefore switches and dims in lockstep with the rest of the circuit. Because the funnel effect only works when the paired fixtures stay matched, the control system catches an outright lamp failure — a voltage rise at constant current, reported as a loop fault — but has no way of detecting a fixture that has merely drifted out of alignment: it still draws normal current and produces no fault at all, so misalignment (see Field Notes) must be caught by physical inspection rather than the control system.

The fixture body is a die-cast aluminium alloy housing, machined and anodised or powder-coated for corrosion resistance against runway de-icing fluids, fuel spillage, and UV exposure. A toughened prismatic lens, tinted green or yellow to match the fixture's assigned colour, caps the optical assembly and is gasket-sealed to the housing with an O-ring or silicone seal to achieve an IP67/IP68 rating against water and dust ingress. Flush-mounted units seat into an L-852 base can recessed into the pavement, with the top surface load-rated for aircraft wheel loading; elevated units instead bolt to a frangible coupling engineered to shear cleanly under aircraft impact loads, seating on an L-861 base can set flush with the surrounding grade. The optics are oriented to project the visual funnel back toward the exiting aircraft, guiding it away from the runway centreline. Internal wiring terminates at L-823 primary connectors, sealed splice connectors rated for direct burial and continuous immersion, which mate to the secondary leads of the isolating transformer housed in its own base can nearby. Stainless-steel fasteners are used throughout to resist corrosion, and the base can assembly includes a drainage provision to prevent water pooling around the transformer and cable entry points.