FX850D / FX850ED Inset Runway Threshold Light

The FX850D (and the dual-end variant FX850ED) is ATG's inset threshold light, the fitting that marks the start of the designated landing surface with a green beam aimed at arriving aircraft. When viewed from behind the threshold — from the runway side — the same fixture displays red, alerting departing aircraft that they are approaching the runway limit. This bidirectional colour combination (green inbound, red outbound) is mandated by ICAO Annex 14 and the FAA AGL specifications for all instrument and visual runways.

The FX850D is configured as a unidirectional green fitting for threshold-only marking applications, while the FX850ED provides the dual-function green/red output needed when the threshold and runway-end coincide or are served by the same inset circuit. Both variants protrude 6.0 mm above the pavement — at the upper end of the FAA Style 3 and ICAO Style 4 limit of 6.3 mm — and install into a standard 12-inch seating pot.

LED technology eliminates the tungsten halogen lamp replacement cycles that historically required frequent short-duration runway closures at the threshold area. Service life exceeds 60,000 hours. The flat no-negative-slope lens prevents sand and water accumulation, and the IP67 housing is compatible with airfield washing and snowplough operations.

For airports following the LED upgrade path, the FX850D connects directly to existing 6.6 A series circuits with an FAA L823 Style 1 connector and is fully dimmable across the CCR brilliancy step range, following FAA Engineering Brief 67 requirements.