The white lines on airport runways play an important role in guiding pilots during takeoff and landing. They provide visual cues that help pilots maintain proper positioning on the runway and stay on the correct glidepath as they come in for a landing. But what exactly are these ubiquitous white lines called?
Runway Markings
The specific white lines painted on runways are known as runway markings. These markings are standardized across airports worldwide in accordance with regulations set by the International Civil Aviation Organization (ICAO). The markings communicate essential information to pilots and drivers operating aircraft and ground vehicles on the airport’s taxiways and runways.
Runway markings serve several key functions:
- Indicate the edges of the usable runway
- Divide the runway into sections
- Mark the touchdown zone where a plane should aim to first contact the runway
- Guide pilots to stay on the runway centerline during takeoff and landing
- Prevent planes from taxiing into unsafe areas
Adhering to the internationally standardized system allows pilots familiar with one airport to readily understand the markings at any other airport around the world. Consistent markings are critical for maintaining safety in the fast-paced, complex aviation environment.
Types of Runway Markings
Runway markings fall into three major categories:
Centerline Markings
As the name suggests, centerline markings delineate the center point of the runway. These are a series of uniformly spaced white dashes that run the full length of the runway. Centerline markings provide pilots with a visual guide to stay aligned with the runway center as they take off or come in for landing. Maintaining centerline alignment is critical for ensuring adequate clearance from the runway edges and avoiding collisions with other aircraft.
Edge Markings
White solid lines along each edge of the runway denote the usable width of the runway. By staying within these edge lines, pilots ensure wingtip clearance to avoid accidents. Edge markings also provide distance references that assist pilots in assessing their position and speed.
Threshold and End Markings
Markings across the runway at both ends identify the runway threshold and end. Threshold markings are a series of longitudinal stripes at the beginning of the usable runway. They indicate the point beyond which the runway should not be used for landing. End markings consist of solid lines perpendicular to the runway to identify its endpoint. These help pilots avoid overrunning the runway during landing or takeoff.
Visual Aids for Pilots
Runway markings work together with other visual cues to guide pilots and increase airport safety. These include:
Touchdown Zone Markings
Touchdown zone markings are a series of solid and dashed lines in the first 3,000 feet of the runway. They give pilots a target to aim for an ideal landing touchdown point. Touchdown markers help ensure adequate runway remains to safely slow down and stop the plane after touching down.
Threshold Markings
Green threshold lights are installed flush with the runway surface at the threshold. They help identify the beginning of the usable runway for landing. Yellow threshold lights stretched across the runway also increase visibility of the threshold point.
Runway Distance Remaining Signs
White signs with black numbers indicate how much runway distance remains. Pilots refer to these signs during takeoff and landing to ensure they do not exceed the available runway length. Exceeding the runway length risks overrunning the runway end.
Aiming Point Markings
Also known as target point markings, these white lines provide pilots a visual aiming point for the touchdown zone. They increase precision and safety during landing. Aiming point markings are highly conspicuous visual aids when visibility is limited.
How Pilots Use Runway Markings
Pilots use runway markings as visual cues for various flight procedures. Here are some examples:
Takeoff
During takeoff, pilots align the aircraft centerline with the runway centerline markings. They track the centerline markings and runway edge lines to accelerate down the runway straight and centered. The markings provide important positional references at high speeds.
Landing
On landing approach, pilots aim for the touchdown zone and aiming point markings. They refer to the large touchdown zone stripes while transitioning to land after crossing the runway threshold. Floating above the touchdown markings during flare allows touchdown in the optimal landing area.
Nighttime Operations
Runway markings are especially critical for nighttime takeoffs and landings when visibility is reduced. Pilots rely on illuminated runway markings to maintain orientation when runway lighting alone provides limited peripheral cues.
Backtaxi
To backtaxi a plane, pilots align the nosewheel with dashed taxiway centerline markings to guide the reverse movement. Solid lines would not be visible backing up. Edge markings prevent drifting off the taxiway.
Rules and Regulations
All runway markings must adhere to international standards published in ICAO’s Annex 14. Key regulations include:
- Runway centerline stripes are at least 30 meters long and 45-90 cm wide
- Regular spacing between centerline stripes ranges from 15-30 meters
- Edge marking stripes are at least 45 cm wide
- Touchdown zone markings consist of symmetrical pairs of solid and dashed lines
In the United States, the FAA enforces specific rules on runway markings under CFR Part 139.311. Airports must keep markings properly maintained and visible to perform their safety functions.
Specialized Markings
In addition to the common markings already discussed, some runways feature specialized markings for certain aircraft performance, operations, or visual effects. Here are a few examples:
Displaced Threshold Markings
A displaced threshold shifts the runway threshold farther down the runway from the physical start point. A section of diagonal yellow chevrons covers the displaced initial section not to be used for landing. Takeoffs can use the full length. Displaced thresholds provide obstacle clearance for landing.
Blast Pads
Some runways feature an extra paved blast pad beyond the end. These provide an emergency overrun area for planes struggling to slow and stop. Bold yellow chevrons cover the blast pad area to show it is not part of the usable runway.
Vortex Generators
These high-visibility orange markings help deter crosswinds along a runway. The markings create small wingtip-like turbulence to counteract crosswind vortex action.
Triangular Runway End Markers
Large yellow right triangles mark the very ends of some runways. This provides highly visible warnings that the paved surface is ending.
Runway Marking Materials
Runways use long-lasting, highly durable materials to mark the surface. Typical materials include:
- Water-based paints
- Epoxy paints
- Thermoplastic markings
- Preformed thermoplastic markings
Factors considered in selecting runway marking materials include visibility, durability, retroreflectivity, and required maintenance frequency.
Creating Effective Markings
Many considerations go into designing optimal runway markings:
- Markings must be thick and bright enough for easy visibility from the cockpit during landing, which is the hardest time to see them.
- Runway surface color is chosen to maximize marking contrast.
- Glass beads are embedded to create retroreflection and enhance visibility.
- Durable materials withstand weathering effects and jet blast forces.
- Reflectivity is continually monitored and maintained for visibility.
- Markings are repainted and restored as needed to preserve function.
Following standardized practices in materials science, engineering, and aviation human factors is key to making markings that effectively serve pilots.
Evolution of Runway Markings
Runway markings have evolved to increase precision and airport capacity:
| Time Period | Marking Advances |
|---|---|
| Up to 1930s | Centerlines introduced on some runways |
| 1940s | ICAO begins developing worldwide standards |
| 1950s | Runway threshold markings introduced |
| 1960-70s | Edge markings, aiming point markings, and touchdown zone markings widely adopted |
| 1980-90s | Markings adapted for new large aircraft like A380 |
| 2000s | Innovative materials like porcelain and preformed thermoplastics used |
Today’s markings allow pilots to maximize use of runways safely. Continuous innovations in materials and markings will support future advances in aviation.
Key Takeaways
The white markings on airport runways serve the vital function of guiding pilots during takeoffs and landings. Key takeaways include:
- The markings are formally known as runway markings and are standardized worldwide.
- Centerline, edge, threshold, and end markings are the main types.
- Markings help pilots stay centered on the runway and avoid dangerous deviations.
- Touchdown zone and aiming point markings facilitate safe landing positioning.
- Pilots rely on illuminated markings for critical visual cues at night.
- Strict global regulations govern key properties of runway markings.
Runway markings have evolved over decades to support aviation safety as runways become busier. The system of markings provides pilots invaluable visual guidance from the moment of touching down through takeoff into the sky once more.
Conclusion
The white lines painted on airport runways may seem simple, but they play an outsized role in guiding pilots and maintaining safety for every aircraft that comes in for a landing or takes off into the skies. The standardized system of runway markings developed by aviation authorities provides visual tools pilots worldwide rely on. While runway markings will continue to evolve with innovations, they already serve as an indispensable component enabling the miracle of flight to safely connect our modern world. So next time you are coasting down the runway for takeoff or touching down gracefully after a flight, take a moment to appreciate those white lines that silently guide your journey.