FX850B Inset Touchdown Zone Light

The FX850B (FAA designation L-850B(L)) is an inset touchdown zone (TDZ) light designed for the critical first 900 metres of the runway beyond the threshold. TDZ lights are mandatory on Category II and III instrument runways; they provide the white rectangular bar arrays that frame the touchdown target area, giving pilots essential lateral and longitudinal visual reference during the final moments of an automatic or manually-flown approach in low visibility.

The FX850B emits a high-intensity clear (white) unidirectional beam oriented toward the approaching aircraft. Its 4.0 mm protrusion sits within the FAA Style 3 and ICAO Style 4 flush-fitting envelope, and the flat lens geometry eliminates the debris traps that form in fittings with recessed or angled lenses — particularly relevant on runways that accumulate blown sand between maintenance cycles.

The fixture installs into a standard 8-inch or 12-inch IEC seating pot and connects via an FAA L823 Style 1 water-tight connector. It operates across the 2.8–6.6 A series circuit current range, dimmable through eight brilliancy steps following the tungsten halogen response curve as required by FAA Engineering Brief 67. Fail-open LED array monitoring integrates with the airfield management system to identify degraded fixtures before they impact approach lighting integrity.

LED service life exceeding 60,000 hours makes the FX850B substantially less maintenance-intensive than the halogen fittings it replaces, an important gain at busy international airports where TDZ light replacement has historically required runway closures at the highest-activity periods.