After crossing the threshold, pilots must complete a touchdown and roll out on the runway. The runway visual aids for this phase of landing are be designed to give pilots information on alignment, lateral displacement, roll, and distance. The lights are arranged to form a visual pattern that pilots can easily interpret.
At first, night landings were made by floodlighting the general area. Various types of lighting devices were used, including automobile headlights, arc lights, and search lights. Boundary lights were added to outline the field and to mark hazards such as ditches and fences. Gradually, preferred landing directions were developed, and special lights were used to indicate these directions. Floodlighting was then restricted to the preferred landing directions, and runway edge lights were added along the landing strips. As experience was developed, the runway edge lights were adopted as visual aids on a runway. This was followed by the use of runway centerline and touchdown zone lights for operations in very poor visibility. FAA Advisory Circular 150/5340-30C provides guidance for the design and installation of runway and taxiway lighting systems.
Runway Edge Lights
Runway edge lighting systems outline the edge of runways during nighttime and reduced visibility conditions. Runway edge lights are classified by intensity, high intensity (HIRL), medium intensity (MIRL), and low intensity (LIRL). LIRLs are typically installed on visual runways and at rural airports. MIRLs are typically installed on visual runways at larger airports and on nonprecision instrument runways, HIRLs are installed on precision-instrument runways.
Elevated runway lights are mounted on frangible fittings and project no more than 30 in above the surface on which they are installed. They are located along the edge of the runway not more than 10 ft from the edge of the full-strength pavement surface. The longitudinal spacing is not more than 200 ft. Runway edge lights are white, except that the last 2000 ft of an instrument runway in the direction of aircraft operations these lights are yellow to indicate a caution zone.
Runway Centerline and Touchdown Zone Lights
As an aircraft traverses over the approach lights, pilots are looking at relatively bright light sources on the extended runway centerline.
Over the runway threshold, pilots continue to look along the centerline, put the principal source of guidance, namely, the runway edge lights, has moved far to each side in their peripheral vision. The result is that the central area appears excessively black, and pilots are virtually flying blind, except for the peripheral reference information, and any reflection of the runway pavement from t lights. Attempts to eliminate this ?black ho of runway edge lights have proven ineffective. In order to reduce the black hole effect and provide adequate guidance during very poor visibility conditions, runway centerline and touchdown zone lights are typically installed in the pavement.
These lights are usually installed only at those airports which are equipped for instrument operations. These lights are required for ILS category II and category III runways and for category I runways used for landing operations below 2400 ft runway visual range. Runway centerline lights are required on runways used for takeoff operations below 1600 ft runway visual range. Although not required, runway centerline lights are recommended for category I runways greater than 170 ft in width or when used by aircraft with approach speeds over 140 kn. When there are displaced thresholds, the centerline lights are extended into the displaced threshold area. If the displaced area is not used for takeoff operations, or if the displaced area is used for takeoff operations and is less than 700 ft in length, the centerline lights are blanked out in the direction of landing. For displaced thresholds greater than 700 ft in length or for displaced areas used for takeoffs, the centerline lights in the displaced area must be capable of being shut off during landing operations.
Runway touchdown zone lights are white, consist of a three-bulb bar on either side of the runway centerline, and extend 3000 ft from the runway threshold or one-half the runway length if the runway is less than 6000 ft long. They are spaced at intervals of 100 ft, with the first light bar 100 ft from the runway threshold, and are located 36 ft on either side of the runway centerline, as shown in Fig. 8-13. The centerline lights are spaced at intervals of 50 ft. They are normally offset a maximum of 2 ft from the centerline to avoid the centerline paint line and the nose gear of the aircraft riding over the light fixtures. These lights are also white, except for the last 3000 ft of runway in the direction of aircraft operations, where they are color coded. The last 1000 ft of centerline lights are red, and the next 2000 ft are alternated red and white.
Runway End Identifier Lights
Runway end identifier lights (REIL) are installed at airports where there are no approach lights to provide pilots with positive visual identification of the approach end of the runway. The system consists of a pair of synchronized white flashing lights located on each side of the runway threshold and is intended for use when there is adequate visibility.