Landing aircraft deposit rubber on the runways, as you will often see if you look at a busy airport runway. Have you ever wondered how this is removed? Letting it build up can be dangerous, so airports have a well-defined process in place to remove it, with chemical, high-pressure water, or air.
Rubber on the runway
Aircraft will usually land in the same area of the runway, known as the touchdown zone. This is standard practice (and guidelines and marking for this are specified in ICAO standards for airports). This is slightly forward of the runway edge (for safety and in case of early touchdown or emergencies) but still allows maximum runway length after landing. It is also strengthened for the extra loads, even down to enhanced foundations.
This area is marked by ICAO-defined markings but is also easily spotted by the presence of rubber marks from previous landings.
The rubber is stripped from aircraft tires during landing. This happens as the stationary wheels begin to spin after making contact with the ground. As they get up to speed, they are dragging on the runway surface. The friction (enhanced by the aircraft’s weight) causes tire rubber to be removed and harden on the runway surface.
Removing the rubber
Leaving rubber on the runway can be dangerous. It reduces the friction with aircraft tires, affecting braking and control of the aircraft. And in wet conditions, the risk of hydroplaning is increased.
As such, all airports remove rubber from the runway surface periodically. How the buildup should be checked and how often is usually mandated by aviation regulators (based on ICAO standards and guidance). This will obviously depend on the runway use. For example, the US FAA advises checking rubber deposits every week for runways with 210 or more daily landings, down to as low as yearly for runways with less than 15 daily landings.
The removal of rubber focuses on restoring the friction of the runway surface. It is not as simple as removing the visible blacks marks. Checking the runway surface involves a physical measure of the pavement friction values, not just a visual inspection.
In fact, some of the markings may remain as to remove them could mean damaging the runway surface; clearly not something you want to do every week at a busy airport.
There are three main ways to remove rubber deposits, with guidance for each given in the ICAO Airport Services Manual (chapter 8). There is a degree of choice for airports in which method to use. But there are some circumstances where some methods are preferable. The following methods are used:
- Use of chemical solvents
- Blasting with high-pressure water
- Use of hot compressed air
Use of chemical solvents
Solvents are applied to the runway surface, left for some time, and then removed with water. Over time, chemical solutions have evolved to be high-performance and not to cause damage to the runway surface. Concrete surfaces use a base of cresylic acid and benzene, while asphalt surfaces use alkaline chemicals.
Such chemicals are expensive and require special handling and removal. The runway is also out of use for the time it takes to apply the treatment (ICAO suggests a standard touchdown zone are could take eight hours for application and removal).
Blasting with high-pressure water
Blasting the surface with high-pressure water causes the hardened rubber to break free from the runway surface. This is usually applied by jet from a specialized water tanker, although smaller airports may use hand-operated sprays.
The pressure used depends on both the equipment (ultra-high pressure equipment is better but more expensive) and the depth of rubber to remove. The surface will usually be tested before to determine the appropriate pressure.
In practice, many airports use a combination of chemical and high-pressure water treatment.
Use of hot compressed air
High-temperature air/gas mixtures can remove rubber in a similar way to water jets. With this method, there is more likelihood of particles being left on the runway surface, so this must be checked and cleaned afterward.
There are also cases of airports using air and abrasive particles (such as sand). This can work but will further increase the risk of debris and foreign object damage.
Would you like to share any thoughts or comments about airport rubber removal or any other aspects of runway maintenance? It’s not a topic we discuss often, so let us know in the comments.