For operations less than 600 feet RVR, it is a necessity for stopbars to be installed at any intersections where the taxiway centreline is illuminated and also at a lighted taxiway and an active runway intersection. These type of are inset fixtures (in-pavement lights) are red in colour, generally unidirectional and installed along the holding position markings Clearance for a pilot or other ground vehicle to proceed is visually achieved when the stopbar is extinguished by the controller. Stopbars located at runway intersections are interlocked with green centreline lead-on lights, which extend from the stop bar location onto the runway.
Normal operation of stopbars include:
- Clearance by air traffic control to a pilot or ground vehicle operator to enter the runway. The deselection of the lights causes the red stopbar to be extinguished and the green lead-on lights to illuminate.
- After a predetermined time or after traveling approximately 100 meters beyond the stopbar, the aircraft or vehicle activates a runway incursion sensor. This sensor automatically relights the stop bar and extinguishes the first segment of the lead-on lights between the stop bar and the sensor. This actions provides added protection for the runway against any inadvertent entry by a trailing aircraft or vehicl.
- The aircraft then activates a further sensor at approximately 120 meters which extinguishes the remaining lead-on lights.
- If for some reason either runway incursion sensor is not activated within a specified time limit, the stopbar will default automatically to “on” and both sections of lead-on lights will be turned “off.”
Runway Guard Lights
Runway guard lights, are installed at all taxiways which provide access to the runway in use. These lights consist of alternately flashing yellow lights and can either be elevated of inset fixtures. The guard lights identify the presence of an active runway and also indicate the location of a runway holding position marking.
Taxiway centreline lighting
For guidance of aircraft and vehicles around the taxiway infrastructure under low visibility conditions taxiway centre line lighting is used. These consist of inset fixtures, that emit green light and are usually bidirectional. Taxiway Centreline. When the taxiway system passes through the ILS protected area the lights are alternate green yellow.
Clearance Bar Lights
To denote holding positions for aircraft and ground vehicles three yellow in-pavement clearance bar lights are installed.
Airfield guidance signs have two purposes.
- Mandatory signs – these give the pilot instruction that they must obey at all times. Before proceeding past this type of sign permission must be sort from air traffic control.
- Information signs – these give the pilots direction to a certain location by the use of arrows and taxiway names. It also provides clear indication as to the precise location where an aircraft or vehicle is located and the names of the taxiway which it is travelling.