Airports everywhere continue changing the name of their runways. This is not because the styles are changing continuously or the rules and regulations keep on changing.
But as a result, the earth’s magnetic field keeps on shifting. It may not sound like it but the continuous replacement of airport signs and repaints costs hundreds of dollars each time. The reason behind this constant modification is that the magnetic north Pole moves as much as forty miles per year.
This extreme variability brings problems for pilots and airports since the runways are named on the basis of how many degrees off north they’re.
Airport Runway Numbering Basics
Wichita’s 14/32 runway can be used from either direction. It’s either 140 degrees from the north or 320 degrees in a different direction. These numbers are rounded to the closest 10 and then shortened to 2 digits.
This is an easy way for pilots to make sure that they’re landing and taking off from the correct strip. However, the earth’s magnetic fields complicate this easy system. The Federal Aviation Agency orders airports to alter the runway names. Once they have been modified to an extent that they are no longer round to the same figure.
For example, a runway that’s named thirty-six won’t have to change its name if the degrees off north went from 355 to 359. However, when it goes to 354, the number must be modified to thirty-five.
HOW ARE RUNWAY NUMBERS ASSIGNED?
Airport runways are numbered according to compass bearings. This means runway numbers are based on the compass with 360 representing north, 90 representing east, 180 representing south, and 270 representing the west. Runways are numbered between 01 and 36.
For runway headings, the last number is dropped and each individual number is pronounced. For instance, a compass heading of 310 degrees would read 31 and be pronounced as three-one.
For the sake of simplicity, the FAA grounds headings to the nearest ten so even if the heading is 308 degrees, the runway would be called three one instead.
Since most runways are oriented to take advantage of prevailing winds to assist in takeoffs and landings, they can be used in either direction. This is why most runways have two numbers. The second number differs by 18 or 180 degrees.
Busy Airports and Runways numbers
Some airports are busier than others. Airports that have two parallel runways going in the same direction are designated as the left or right runway with an L or R. In this case, runway 31 would be called 31R or 31L. If there are three parallel runways, the designation of C will be assigned to the runway in the center. In this case, you would have 31L, 31R, and 31C.
Exceptionally busy airports like ATL in Atlanta and LAX in Los Angeles may have more than three runways parallel to each other. In these instances, even though all runways have the same heading, the number for some of the runways is shifted by ten degrees, making for a one-digit difference.
In the case of DFW (Dallas-Fort Worth), there are five runways with the same heading. Those on the east side of the airport have the traditional L, R, and C designations according to standard runway numbers, while those located to the west have been increased by 10 degrees while utilizing the L and R designations.
This process is currently happening at the Wichita Eisenhower International airport. Runways 1L/19R, 1R/19L. The numbers refer to parallel runways and the R and L represent the left and right.
The 14/32 will be modified to 2L/20R, 2R/20L, and 15/33. After 1954, this is the first time the runways will be renamed. Many times, the distinction doesn’t even matter much since the pilots can visually determine the correct runway. However mislabeling can also cause serious consequences like the 2006 Comair Flight 5191 crash in Lexington, Kentucky. The crash killed forty-nine individuals.
The investigation of the case revealed that the crew couldn’t correctly determine the runway. And took off from the shorter runway that resulted in the crash. Keeping up with the constantly changing magnetic fields can be a bit of a pain and extra effort. However, as long as it is keeping the flights safe, it’s worth all the effort.
1- Single Physical Runways
A runway designator consists of a two-digit number, which is the whole number nearest to one-tenth of the magnetic North when viewed from the direction of approach. For example, if the azimuth of the centreline is 153 then the runway designator will be 15.
When this rule results in a single-digit number then the designator is preceded by a zero (e.g. if the runway centerline azimuth is 82, then the designator will be 08). North-oriented runways are designated 36 (not 00). In simple words, the runway designator represents the heading used for taking off or landing on the runway.
If the runway is used in both directions, then each of them receives its own designator. This means that although there is one physical surface used for take-offs and landings, it is treated as two runways. The difference between the numbers is 18, e.g. if one of the runways is 12 then the other will be 30.
2- Parallel Runways
On parallel runways, the number is supplemented with a letter that defines the relative position of each of them. The possible letters are L (left), R (right), and C (center), in line with the point of view of the observer standing at the runway threshold.
For example, two parallel runways (East direction) would be designated as 09L and 09R. If the runways were three, then the designations would be 09L, 09C, and 09R. Note that the opposite ends (27 in this case) would also include the observer’s viewpoint, which means that the opposite direction of 09L would be 27R and vice versa.
Example of three parallel runways. Note that the opposite end of 18 left is designated as 36 right
If more than 3 parallel runways exist, then some of the runways are named to the nearest one-tenth magnetic azimuth and the other adjacent runways are designated to the next one-tenth. For example, a group of four parallel runways (facing North) can be designated as e.g. 36L, 36R, 35L, and 35R.
Example of four parallel runways
In the case of parallel runways, each runways numbers designation number shall be supplemented by a letter as follows, in the order shown from left to right when viewed from the direction of approach:
- two parallel runways: “L” “R”;
- three parallel runways: “L” “C” “R”;
- four parallel runways: “L” “R” “L” “R”;
- five parallel runways: “L” “C” “R” “L” “R” or “L” “R” “L” “C” “R”;
- six parallel runways: “L” “C” “R” “L” “C” “R”.