Runways: True Or Magnetic North?

Runway numbers are based on compass headings, with each number corresponding to the closest magnetic heading of the runway, rounded to the nearest 10 degrees. For example, if a runway heading is 092°, the runway number will be 09, as the heading is rounded to the closest 10° (090°) and the final '0' is removed. This system is used because it is simple and reliable, and it helps pilots locate the correct runway. The magnetic north pole moves over time, so runway numbers are updated to reflect this.

Airport runway numbers are based on compass headings

Runway numbers are based on compass headings, specifically magnetic headings. This is because, in the early days of aviation, magnetic compasses were the only tool available for determining direction. Even today, magnetic compasses are still used as primary instruments for navigation in aviation, alongside GPS instruments.

Runways are numbered based on the magnetic azimuth (compass bearing) in which a runway is oriented. There are 360 degrees on a compass rose, and runway numbers are determined by rounding the compass bearing of one runway end to the nearest 10 degrees and then removing the last digit, resulting in runway numbers from 1 to 36. For example, if a runway has a compass bearing of 092°, the runway number would be "09".

The opposite end of the runway will always differ by 180 degrees, so it is numbered 18 higher or lower. For instance, Runway 9-27 is oriented east-west. If you are taking off easterly on Runway 9-27, you are considered to be using Runway 9 for departure.

Additionally, large airports often have multiple runways pointing in the same direction, known as parallel runways. To differentiate between these runways, letters are added to the number. For example, if there are two runways pointing to a 350° magnetic heading, they would be numbered "35L" and "35R" for left and right, respectively.

It is important to note that runway numbers are always given in terms of degrees magnetic and are referenced to magnetic north, not true north. This is because the magnetic north pole shifts over time, and using magnetic headings ensures that runway headings remain accurate. When magnetic north shifts enough to affect the nearest 10-degree rounding, the runway numbers are changed accordingly.

Runways are numbered from 1 to 36

Runway numbers are based on the compass heading, or the magnetic azimuth, in which a runway is oriented. There are 360 degrees on a compass rose, and runway numbers are determined by rounding the compass bearing of one runway end to the nearest 10 degrees and truncating the last digit, meaning runways are numbered from 1 to 36.

The runway numbers tell pilots where the runway is pointing, in reference to magnetic north. The numbers are a quick and easy system for pilots to work out which direction they are taking off and landing in.

The compass bearing of a runway is rounded to the nearest 10 degrees, and the zero is removed. For example, if a compass reads 092°, the runway number will be 09. This is because the 092° is rounded to the closest 10° (090°) and then the final ‘zero’ is removed to give a two-digit identifier.

The direction a runway faces is determined by several factors, including the predominant prevailing wind trend, noise abatement and nearby residential areas, and existing infrastructure.

The magnetic north pole moves, so runway numbers change over time

Runway numbers are determined by rounding the compass bearing of one runway end to the nearest 10 degrees and then removing the last digit, resulting in runway numbers from 1 to 36. The numbers are a reference to the closest magnetic heading of the runway. This is because, in the early days of aviation, magnetic compasses were the only tool available for determining direction.

However, the magnetic north pole moves. Over many years, the geomagnetic iron drifts, causing the magnetic north to shift slightly. As a result, runway numbers change over time. If the shift is significant enough that the runway heading no longer corresponds to the nearest 10 degrees, the numbers are changed to reflect this. For example, the Fairbanks International Airport in Alaska changed runway 1L-19R to 2L-20R in 2009 when magnetic north shifted enough to mandate a change.

Runways at high latitudes, closer to the poles, must make more frequent adjustments than runways closer to the equator, as magnetic shifts happen faster in these areas. For instance, Fairbanks International Airport has to change its runway numbers roughly every 24 years.

Airports closer to the poles have to update runway names more frequently

The Earth's magnetic field is in a constant state of flux, with large-scale changes occurring over several thousand years, and smaller changes affecting navigation systems over shorter periods. Airports name their runways according to their magnetic bearing, with the numbers painted on both ends of the runway, shown on sign panels, and used when communicating with air traffic control. These numbers are based on the runway's magnetic bearing, indicating their position relative to the Earth's North Magnetic Pole.

Runway numbers are calculated by rounding the runway heading to the nearest 10 degrees and removing the final digit. For example, a runway with a heading of 092° will be named "09", as 092° rounded to the nearest 10 is 090°, and then the final "0" is removed.

The North Magnetic Pole moves by around 60km per year, or 40 miles per year, and this movement affects runway names. If the compass bearing rounds off to another decadegree, the runway must be renamed based on international aviation regulations. Airports closer to the poles experience faster magnetic shifts, and so must make more frequent adjustments to runway names than airports closer to the equator. For example, Fairbanks International Airport in Alaska, which is closer to the North Pole, has to change its runway names roughly every 24 years. In contrast, Denver International Airport, which is closer to the equator, will not need to change its runway names for another 30 years or more.

Runway markings are always white

Runway markings include the following:

• Runway Designators: Large numbers painted at both ends of a runway, indicating the runway's magnetic orientation.
• Centerline: A dashed white line running down the middle of the runway, guiding pilots during takeoff and landing.
• Aiming Point Markings: Two thick white rectangles about 1,000 feet from the landing threshold, providing a visual cue for pilots on where to touch down.
• Touchdown Zone Markers: Pairs of white bars indicating the safest area for landing.
• Side Stripes: Continuous white lines along the edges of the runway, defining its safe operational boundaries.
• Threshold Markings: A series of white stripes at the beginning of the runway, signalling the start of the landing area.

In addition to these white markings, Runway Shoulder Markings are yellow and indicate areas adjacent to the runway that are not intended for aircraft use.

The uniformity in runway markings from one airport to another enhances safety and improves efficiency. Pilots who encounter ineffective, incorrect, or confusing markings are encouraged to report them to the airport operator and the FAA regional airports division.

Frequently asked questions