Everything You Need To Know About Runway Surface Friction

by | Sep 4, 2024 | Uncategorized

Aircraft tire landing on a runway with smaller graphic of aircraft taking off

Read Time: 3 Minutes

Runway surface friction is essential for aircraft safety, especially during landings and takeoffs. Friction helps aircraft maintain control, decelerate, and avoid skidding, but contaminants like rubber deposits, jet fuel, and de-icing fluids can cause life-threatening accidents for landing aircraft.

A Brief History of Runway Friction

In the early days of aviation, runways often lacked adequate friction, leading to dangerous landings in wet conditions. To address this, the FAA introduced guidelines for adding macrotexture grooves to runways, improving water drainage and reducing the risk of hydroplaning. This advancement significantly enhanced runway safety and remains a crucial part of modern runway design.

How Runway Friction Is Lost

Maintaining optimal runway friction is essential for safe aircraft operations. However, friction is often reduced due to several contaminants:

  • Rubber Deposits: As aircraft land, their tires accelerate from 0 to around 150 mph, leaving behind rubber deposits. The carbonized rubber residue accumulates on the runway over time, covering both the microtexture (fine pavement roughness) and macrotexture (larger-scale grooves) of the runway. This buildup significantly reduces the traction of aircraft, especially during wet conditions when the rubber becomes slick.
  • Jet Fuel: Fuel spills during aircraft operations can create slippery spots on the runway, contributing to friction loss and increasing the risk of skidding during landings and takeoffs.
  • De-Icing Fluids: While necessary for removing ice in cold weather, de-icing fluids can also reduce surface friction when left on the runway.

Maintaining Runway Surface Friction

Regular runway maintenance is crucial to ensure friction levels remain safe for aircraft operations. Friction testing is required before and after rubber removal, and involves using Continuous Friction Measuring Equipment (CFME) to assess the level of grip between the runway surface and aircraft tires. These devices simulate aircraft landings by towing the self-wetting trailer behind a truck, which measures surface friction and provides data to determine if the runway is within safety standards.

When friction is lost due to rubber buildup, rubber removal becomes necessary to restore the runway’s texture and friction. There are two common methods for removing rubber:

  • Chemical Removal: Chemical solutions are applied to the runway to break down rubber deposits, allowing for easy removal without damaging the surface. Chemical removal is cost-effective at just pennies per square foot, and can be done using standard equipment and in-house personnel. Some formulas like Avion offer eco-friendly products that abide by more recent environmental standards, making them a preferred method for many airports.
  • High-Pressure Water Blasting: This method uses jets of high-pressure water to blast away rubber buildup. While effective, water blasting can potentially damage the runway surface if not carefully conducted, leading to the need for additional maintenance. These machines can also be used to restore the microtexture on the runway surface.

Further Solutions for Restoring Friction

In cases where a runway’s surface has become polished or worn, additional measures may be required to restore friction:

  • Shot Blasting: This method propels small steel balls onto the runway surface to roughen it and remove contaminants. This is often used when polishing or wear has reduced the effectiveness of both microtexture and macrotexture, or when removal of runway paint is desired.
  • Mechanical Resurfacing: When the runway surface becomes overly worn, mechanical resurfacing can remove the top layer of pavement and restore the original texture.

Regulatory Requirements for Friction Testing and Rubber Removal

Airports must follow strict guidelines from regulatory bodies like the FAA and ICAO to maintain runway friction. Regular friction testing and rubber removal ensure that runways remain safe for aircraft operations.

The FAA mandates friction testing when friction coefficients fall below 0.50 during wet conditions. Testing must also be done at regular intervals or after weather events that could affect runway friction.

FAA guidelines specify that the depth of macrotexture grooves should be 1/8 to 1/4 inch. These grooves help channel water away from the surface, maintaining friction and reducing hydroplaning risks.

Rubber removal is necessary when:

  • Friction falls below acceptable levels based on testing.
  • Buildup visibly obstructs microtexture and macrotexture.

Maintaining friction through timely rubber removal ensures regulatory compliance and safe runway conditions.

Avion and GripTester Products for Runway Friction

For airports looking to maintain safe friction levels, Avion50 offers a powerful solution for chemical rubber removal, restoring runway texture and friction without the risks of surface damage. Paired with accurate friction testing equipment, like the GripTester, airports can ensure that their runways remain within safety standards before and after maintenance operations.

Further Reading