The runway markings and lighting are essential for the safe operation of aircraft. The markings are used by pilots to determine the runway orientation, how much distance is left and to make other critical judgments during takeoffs and landings. The lighting is used during the night and low visibility operations. Both the markings and lighting on a runway are highly standardized.
The runway designation marking
The number written on the runway denotes the identification of the runway. The number is the magnetic heading or bearing to the runway. For example, if the runway is labeled 36, then the bearing to that runway is 360 degrees. Conventionally, only two digits are used to mark a runway. As seen in the example, the zero in 360 is dropped. Similarly, if the heading to the runway is 90 degrees, the last zero is dropped. However, in this case, a zero is added ahead of the number 9, making it runway 09. This avoids confusion as a heading of 900 degrees does not exist.
When an airport has parallel runways (runways with the same bearing), the number is supplemented with a letter code. Most airports use L (Left), R (Right), and C (Centre) for parallel runways. The runway to the right is labeled R, the one to the left is labeled L and the center runway is labeled C.
The Runway Threshold Marking
The runway threshold marks the start of the runway. It consists of stripes that are about 30 m in length and about 1.8 m in width. The number of stripes depends on the actual width of the runway.
The threshold strips are unofficially known as “piano keys” as when they are placed on the runway, they have the appearance of a set of keys on a piano.
In some airports, there exists are portion behind the runway threshold known as a displaced threshold. This area is marked with arrows pointing to the threshold. The displaced threshold is an area where it is prohibited to land an aircraft. However, takeoffs can be conducted using the area.
The Runway Aiming point and Touch-down zone Marking
The Aiming point consists of two large white stripes marked on the runway. It is the point on the runway where the pilots aim to touch down during the approach. The length, width, and distance from the threshold where the aiming point must be painted depending on the runway length. Please refer to the table below for further information regarding this:
The touch-down zone marking helps pilots quickly determine the runway distances remaining during the final parts of the landing. The markings consist of pairs of rectangular stripes drawn symmetrically about the runway center line. The number of touch-down zone markings that need to be painted on the runway depends on the landing distance available or the distance between the thresholds of the runways. Please refer to the table below to get an idea about this:
The touch-down zone marking stripes can be one, two, or even three closely spaced stripes. When one pair of stripes is used, the length of the stripe should be at least 22.5 m, and the width must not be less than 3 m. When two or three stripes are used, the width may be reduced to 1.8 m, and there must be 1.5 m between each stripe.
The touch-down zone markings shall be placed within 150 m intervals starting from the runway threshold. If the runway length makes the touch-down zone marking closer than 50 m to the aiming point, this marking must be deleted.
The Runway Centerline Marking
Runway center line markings are provided to mark the center of the runway. They consist of uniformly placed stripes with a space between them. The space shall not be less than 50 m and not more than 75 m, and each stripe shall be at least equal to the length of the gap or 30 m, whichever is greater.
The width of the stripes depends on the type of approach the runway is designed for. It shall not be less than:
- 0.9 m on CAT II and CAT III approach runways
- 0.3 to 0.45 m on non-precision approach and non-instrument runways.
Runway Lighting system
Runway Edge lights
Runway Edge lighting should be provided for a runway that is intended to be used for night operations. It should be provided for day operations when the Runway Visual Range (RVR) falls below 800 m.
Runway edge lights must be placed not more than 3 m from the outer edge of the runway surface. For an instrument runway, the distance between each light should not be more than 60 m, and for a non-instrument runway, it should not exceed 100 m.
The lights must be white lights. However, in case the runway has a displaced threshold, the lights between the start of the runway and the displaced threshold should be red lights for landing aircraft. Also, for the last 600 m of the runway or one-third of the runway length (whichever is less), the edge lights must be yellow.
Runway Threshold lights
The runway threshold lights are provided to mark the start of the runway. If there is a displaced threshold, the lights should be placed in a row right angle to the runway axis at the displaced threshold. It consists of at least six green lights, and the distance between the lights depends on the type of approach the runway is certified for.
Runway End lights
The end lights are placed on a line right angle to the runway axis on the end of the runway. It should consist of at least six red lights. This is to show the end of the runway to the pilots.
Runway Centre line lights
The center line lights must be provided on a runway designed for CAT II and CAT III precision approach operations. It must also be provided on a runway that is used for takeoff operations with minima below RVR of 400 m.
The center line lights must be fixed white lights from the runway threshold to the point 900 m from the runway end; alternate red and white from 900 m to 300 m from the runway end; and red from 300 m to the end of the runway. When the runway length is less than 1,800 m, the alternate red and white should extend from the midpoint of the runway usable for landing to 300 m from the runway end.
Runway Touch-down zone lights
The touch-down zone lights should be provided in the touch-down zone of runways that can handle CAT II and CAT III precision approach operations.
The lights extend from the threshold to 900 m, except on runways less than 1,800 m in length. In this case, the length of the lighting should be shortened so that it does not go beyond the runway mid-point.
The lights are barrette type (a lighting system with three or more lights closely packed together). The spacing between each light on the barrette should not be more than 1.5 m, and the barrette should have a length of at least 3 m and not more than 4.5 m.
Runway Approach Lighting system
An approach lighting system is required to provide the pilots with alignment and roll guidance in the night and low visibility operations. There are three main approach lighting systems. The Simple Approach Lighting System (SALS), the Precision Approach CAT I lighting system, and the Precision Approach CAT II/III lighting system.
Before we go into further details, it is important to note that there are two types of approach lighting systems. The ICAO system and the Calvert system. The Calvert system was developed by E.S. Calvert of Royal Aircraft Establishment, Farnborough, UK, at the request of the UK civil aviation ministry. The system was first commissioned in the early 50s.
Simple Approach Lighting System (SALS)
The SALS consists of a row of lights that are extended from the runway center line to 420 m from the threshold. A crossbar of 18 m or 30 m in length must be placed at 300 m from the threshold.
The center line lights must be placed at intervals of 60 m. This may be reduced to 30 m to improve the guidance. The crossbar lights may be spaced 1 to 4 m apart.
The lights may be either a single source or a barrette of at least 3 m in length. SALS is used in non-instrument runways and also on non-precision approach runways.
Precision Approach CAT I Lighting system
This type of lighting consists of a row of lights extended from the runway center line to 900 m from the runway threshold. In the ICAO system, a crossbar of 30 m in length must be placed at 300 m from the runway threshold.
In the Calvert system, 5 crossbars are 150 m apart and form three segments; the inner segment (0-300 m); the middle segment (300-600 m), and the outer segment (600-900m). As the crossbars move away from the runway, the length of the crossbars increases in this system.
The light source in the inner segment of the center line should be a single source, two light sources must be provided for the middle segment and three light sources must be provided for the outer segment.
Precision Approach CAT II/III lighting system
In this type of approach lighting system, a row of lights is extended from the runway center line to 900 m from the runway threshold. It must also be equipped with side rows of red barrettes extending 270 m from the threshold. The red lights are used to enhance the pilot’s visibility during the very last segment of the approach.
When it comes to crossbars, there must be at least two of them. One placed 150 m from the threshold and the other 300 m from the runway threshold.
The Calvert system is similar to the ICAO system except that there are 5 crossbars placed as in the Precision Approach CAT I lighting system.
Precision Approach Path Indicators (PAPI)
To aid the pilots in the visual segment of the approach, a PAPI light is provided. It consists of 4 lights which either show red or white. The PAPI is normally set for a 3-degree glide. When on glide, the PAPI indicator shows 2 whites and 2 reds. When high on the glide path, it shows 4 whites and 1 red. And when low on the glide, it shows 4 reds and 1 white. When very high on the approach, it shows all whites, and when very low on the approach, it shows 4 reds.
Source: simpleflying.com