Did you ever look out of an aircraft window and notice the paint marking on the airport runway and wonder what they all mean? Runway paint markings are visual markers that help guide pilots and ensure safe aircraft take-offs and landings. And, if you’re intrigued to understand more about these markings and how they help pilots read on!
To avoid over-complicating the matter I’m going to focus mainly on precision approach runways which are supplemented with instrument landing systems, that are commonly used at major international airports. Simpler, non-instrument runways can have slightly different runway marking layouts.
Airport Runway Markings – Standards
The first thing to realize is that runway markings are almost exclusively white in color and should not be confused with other airport pavement paint markings for taxiways and aprons (ramps) that are yellow in color. However, there are some rare exceptions to this rule.
In Japan and Norway certain airports that experience a lot of snow have yellow runway markings to help the markings stand out more.
As you would expect, given the international nature of air travel, there are international standards for airport runway markings.
These are defined in the International Civil Aviation Organization (ICAO) document – International Standards and Recommended Practices, Annex 14 to the Convention on Civil Aviation, Aerodromes, Volume I, Aerodrome Design and Operations, commonly known as ‘Annex 14.’ Annex 14 sets out the international standards for runway markings in Chapter 5 (Visual Aids for Navigation), Section 5.2 (Markings).
Runway Number Designation Marking
The most familiar runway marking to most people is the runway number designation marking at the runway ends. But what does this mean and what is its significance?
Pilots need to be 100% sure that they are taking off or landing on the correct runway. And whilst many aircraft are automatically guided on landing, and air traffic controllers also manage aircraft movements both in the air and on the ground, the runway designation marking is an added visual aid to pilots confirming the correct runway use.
Runways are numbered based on their compass-bearing directions. If you imagine a compass, with 360° representing north, 90° representing east, 180°, south, and 270° denoting west, runways are numbered between 01 and 36. I.e., the end zero is dropped from the magnetic heading that the runway is facing. A due west-facing runway has a compass heading of 270° and a runway designation of 27. Usually, a runway operates in both directions, so the other end of this runway will face due east and have a compass heading of 90° and a runway designation of 09.
All runway designations contain two digits, and for bi-directional runways, if you subtract the smaller designation number from the larger, the difference is always 18 because of the 180° difference in compass directions.
Some airports have parallel runways and therefore these runways have the same number designation. But to avoid pilot confusion these runways are designated ‘L’ for left and ‘R for right e.g. 27L/09R. In the case of three parallel runways, the middle runway has a ‘C’ (for Center) included.
Other Runway Markings
Below is an overview of other common markings you will see on airport runways.
The runway threshold is marked as a series of longitudinal bars looking like piano keys, at least 30m long, parallel to the runway centerline. The number of bars spread across the runway depends on the runway width.
These markings pinpoint the touchdown zone for landing aircraft. Touchdown zone markings are grouped into one, two, and three rectangular bars arranged in pairs 150m apart, with one of each pair placed on each side of the runway centerline. Each bar is a minimum of 22.5m long and 1.8m wide.
The number of touchdown zone marking pairs is related to the length of the runway and can vary from one to six pairs. The number of bars in each marking pair decrease from three to two, to one, along the length of the touchdown zone, and this diminishing pattern provides vital distance information to the pilot (similar to highway exit countdown markers).
Aiming Point Marking
The aiming point consists of two thick bars within the touchdown zone each up to 60m long and up to 10m wide. The aiming point is usually located 400m from the start of the runway.
The centerline of a runway provides alignment guidance to pilots, helping them to maintain a central position on the runway during take-off and landing. The runway centerline consists of a line of stripes positioned along the center of the runway, 30m long and separated by 20m gaps.
Runway Side Stripes
The runway side stripe markings on each side of the runway delineate the edges of the runway pavement.
Displaced Runway Thresholds
Sometimes a displaced runway threshold is needed and this relocates the aircraft’s final approach path further down the runway so that aircraft maintain a higher altitude as it approaches the runway. Displaced thresholds are normally used to ensure the safe clearance of an obstacle within the runway approach path.
Whilst a displaced threshold reduces the runway length available for landing, aircraft that are taking off can use the portion of the runway before the displaced threshold to ensure the maximum runway length is available for the take-off run.
Displaced thresholds need to be clearly marked so that pilots land on the appropriate part of the runway. Displaced threshold markings include a transverse bar across the width of the runway prior to the threshold marking, and a series of arrows 30m long and 20m apart located prior to the transverse bar.
You can see that there is quite a lot of thought that has gone into the specification of runway markings. The key purpose of these markings is to provide visual cues and guidance to assist the pilot during take-off and landing.
As civil aviation is an international business spanning continents and many jurisdictions it is important that there are international standards for runway (and other airport pavement) markings. It would be too confusing and demanding to expect pilots flying all over the world to understand a variety of different standards applied at the national level.
I hope this short article has provided some insight and has sparked some interest in a topic that you may have otherwise not given too much thought to!