Numbering Logic of Airport Runways

March 10, 2025 • ☕️ 7 min read • 🏷 aviation, airplanes

Translated by author into: English

Orjinali oku • View all translated posts

Air transportation has become an indispensable element of modern societies. While thousands of aircraft land and take off every day in the world, airports are designed in a precise order to ensure that these operations can be carried out safely and effectively. One of the most basic elements of this order is the naming of airport runways and the numbers at the beginning and end of the runway. In this article, the meaning, use and details of the naming system of runway numbers, which are extremely critical in aviation, will be examined in detail.

Basic Logic of Runway Numbers

The numbers at the beginning and end of runways at airports are determined to indicate the direction of the runways. Runway numbers are not arbitrary; each number corresponds to the direction of the runway relative to magnetic north. Every runway on Earth is aligned with magnetic north, and this alignment angle determines the runway number.

For example, if the number at the beginning of a runway is 09, this indicates the approximately 90 degree angle that the runway makes with magnetic north. Therefore, when an aircraft lands on this side of the runway, the aircraft’s nose will be pointing approximately east (90° magnetic direction). If the runway number is 27, this means that this is the exact opposite end of the runway, pointing 270 degrees to magnetic north; in this case, the aircraft will land or take off due west (270° magnetic direction).

Details of the Numbering System and Special Cases

The runway numbering system is basically based on magnetic compass directions and includes the following rules:

1. Calculation of Runway Numbers

When determining the runway number, the magnetic direction is divided by 10 and rounded to the nearest integer. For example: • A runway with a magnetic direction of 183° is numbered 18. • A runway with a magnetic direction of 187° is numbered 19 (rounding upwards from 186°).

2. Double-Ended Numbering

Since each runway has two directions, the runway numbers will always be opposite each other (180 degrees apart). Therefore, if one end of the runway is 03, the other end will be 21 (03 → 30°; 21 → 210°). For example, if the numbers of a runway are 04 and 22, one direction of this runway is 40° and the opposite direction is 220°.

3. Double or Triple Runway Situations (Left, Center, Right)

There may be more than one parallel runway at large airports. In this case, a letter is used in addition to the runway number: • “L” (Left) • “C” (Center) • “R” (Right)

For example, at Istanbul Airport, the parallel runways are named 17L, 17C and 17R. The numbers here indicate that the runways are oriented south (170°) and are arranged in the order of “left-center-right”. The existence of parallel runways provides great convenience and safety in managing air traffic.

4. Magnetic Direction Changing Over Time and Renumbering Runways

Runway numbers at airports are determined by taking the magnetic north on Earth as a reference. However, it is known that the magnetic poles on Earth are not fixed and constantly move over time. This situation causes differences between the magnetic direction when the runways are first determined and the magnetic direction that has developed over the years. For this reason, runway numbers may need to be reviewed and updated from time to time.

The magnetic north pole of the Earth is constantly moving due to geological and magnetic activities. This movement usually occurs at a rate that can vary from a few kilometers to a few tens of kilometers per year. As a result of this shift, the actual magnetic direction of a runway at an airport may deviate by several degrees from the time the first numbering was made. For example, a runway that was initially aligned at 180 degrees (runway number 18) may shift to 184 or 185 degrees over the years as magnetic north moves. This situation makes it necessary to renumber the runway.

According to international standards, if the magnetic direction of the runway deviates by 5 degrees or more from its current numbering, the runway numbers must be updated. This is to protect flight safety by ensuring that the runway numbers remain consistent with the pilots’ navigation systems and compasses. A 5-degree difference is a critical threshold that can cause a pilot to deviate from the runway during the approach phase and experience landing problems.

One concrete example of such changes occurred in 2011 at Tampa International Airport in Florida, USA. Due to significant deviations in the magnetic directions of the runways at the airport, all runways were renumbered and renewed. Similarly, at Calgary International Airport in Canada and many other airports, runway numbers were adjusted due to changes in magnetic north.

Although these updates may seem simple, they actually involve major logistical operations. Because updating runway numbers requires changing the airport’s runway signs, navigation maps, pilots’ flight plans and all documentation used by air traffic controllers. At the same time, updates are required on internationally published flight maps (such as Jeppesen charts) and electronic navigation systems. These processes are meticulously coordinated by aviation authorities and are usually announced in advance and communicated to all stakeholders in the aviation sector.

The Importance of Using Runway Numbers and Their Role in Safety

Runway numbers are of critical importance to pilots, air traffic controllers (ATC) and airport operations teams. Because runway numbers are the most basic references that determine the takeoff and landing routes of aircraft, especially runway approaches. In order to reduce the risk of errors and prevent operational confusion during the most critical stages of flight, landing and takeoff, it is imperative that runway numbers are clear, accurate and up-to-date.

In addition, runway numbers are used as a direct reference in meteorological reporting (METAR), flight plans and air traffic control instructions. Pilots, especially in low visibility conditions (fog, heavy rain, snow, etc.), see the runway numbers on radar and navigation devices to ensure correct alignment and landing.

Misuse and Risks

In the aviation industry, the correct use of the numbers at the beginnings and ends of airport runways is extremely critical. Since these numbers are the basic reference points of flight operations, their misunderstanding or misuse can lead to serious accidents and dangerous situations.

Especially at large and densely trafficked airports, when there are multiple parallel runways, it is very important to clearly understand the additional letters (L-Left, C-Center, R-Right) used next to the runway numbers. For example, if a pilot or air traffic controller mistakenly uses the runway number “26R” instead of “26L”, this can lead to the risk of collision with other aircraft on different runways during landing or takeoff. There are examples in aviation history where such situations have turned into accidents due to incorrect runway selection.

In addition, miscommunication or misreading of runway numbers poses a greater danger in low visibility conditions (fog, rain, snow, night conditions). In these situations where visibility is limited, pilots may have difficulty physically seeing the runway numbers and are completely dependent on the information provided by air traffic controllers and navigation devices. At this point, even a small error in communication can cause the pilot to land on a wrong runway or to be misaligned, jeopardizing flight safety.

Another critical risk is misunderstanding or incorrectly saying the numbers during radio communication between the air traffic controller and the pilot. Confusion of runway numbers due to possible interference on the radio frequency or rapid conversations in heavy traffic situations is a common problem. Such situations can lead the pilot to make unexpected maneuvers or runway incursions, which can lead to extremely dangerous situations.

In order to minimize these risks, aviation authorities and international organizations (such as ICAO, FAA, EASA) have developed standard communication procedures. In line with these procedures, the terminology used by pilots and air traffic controllers has been standardized. For example, it is mandatory to always say the numbers one by one (for example, the runway number “18” is expressed as “one eight”) and repeat the instructions. Additionally, it is critical to keep runway numbers up to date in all written and digital sources, provide training to pilots and conduct regular drills.

Runway numbers at airports are much more than just numbers. Each number is critical to aviation safety, the management of flight operations and the use of airport infrastructure. This numbering system, based on magnetic orientation and standardized globally, ensures clear and reliable communication between pilots and air traffic controllers. Keeping this system accurate and up-to-date is essential for safe aviation operations.

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