Runway Threshold Identification Lights
Runway Threshold Identification Lights (RTILs), sometimes referred to as Runway End Identifier Lights (REILs), are installed at many airports to provide rapid and positive identification of the approach end of a particular runway. The system consists of a pair of synchronized flashing lights located laterally on each side of the runway threshold. REILs may be either omnidirectional or unidirectional facing the approach area.
These are provided at aerodromes where terrain precludes the installation of approach lights, or where unrelated non-aeronautical lights or the lack of daytime contrast reduces the effects of approach lights. When an aerodrome is equipped with RTILs, it is indicated in the CFS by the notation “AS”.