The Stopping Power of Pavement

The FAA’s new runway friction research is aimed at improving landing safety

A Royal Netherlands Aerospace Centre Cessna Citation test aircraft brakes through a water pit formed on a runway at the NASA Wallops Flight Facility in Virginia to collect wet runway braking data. The pilot reduces thrust to idle immediately before entering and applies maximum braking while in the water at speeds ranging from 50 to 100 knots. (Image: FAA)

By Curt Biberdorf, FAA

The FAA is researching how to improve a pilot’s landing distance assessment before touching down in wet conditions and has also approved another way of reporting runway conditions after landing when a surface is contaminated by rain, slush, snow, or ice.

“Recent landing overruns have raised questions regarding some of the current models, standards, and guidance materials found in regulations,” said Somil Shah, an aerospace engineer at the FAA William J. Hughes Technical Center.

One example was a United Express Embraer ERJ-145 that slid off a runway at Ottawa International Airport in Canada in 2010. During the accident investigation, comparing the wet runway braking model to the actual braking friction found an almost 50 percent reduction in braking capability.

A rubber damming material placed on a runway at the NASA Wallops Flight Facility in Virginia forms a water pit to allow researchers to change the water depth and roll the aircraft into it at different speeds to cover the test matrix. (Image: FAA)

In 2023, the FAA worked with the Royal Netherlands Aerospace Centre (NLR) in runway braking testing to evaluate the effects of water level thickness and ground speed on braking performance.

NLR’s Cessna Citation test aircraft splashed through standing water on a runway at speeds up to 100 knots at the NASA Wallops Flight Facility in Virginia. FAA staff measured the pavement friction of the runway and skid resistance.

Data analysis and reporting is set to be completed in 2024 and may result in changes to the wet runway braking models that pilots can use to determine the distance needed to safely stop.

After an aircraft lands on a surface contaminated by liquid or frozen precipitation, the pilot evaluates braking ability. Through a different research effort, pilots now also can use information measured and reported from sensors on the aircraft.

A British pendulum tester measures skid resistance, and an Ames Engineering laser texture scanner estimates runway properties to enable research staff to correlate the information with flight test data collected during testing on a runway at the NASA Wallops Flight Facility in Virginia. (Image: FAA)

The FAA evaluated two prototype systems that collect data from the aircraft to report on runway conditions and concluded they were feasible. The agency developed updated guidance for airlines to incorporate them into their operations.

“These systems don’t necessarily have to be perfect, but they are much more accurate than the subjective-based system,” said Angela Campbell, an aerospace engineer at the FAA William J. Hughes Technical Center. “The technology works. Based on the research, we have a lot of faith in it.”

The FAA plans to establish an objective, data-driven assessment of the runway condition that relies mainly on aircraft braking action reports and can be supplemented by pilot braking action reports.

With better modeling and improved information on runway braking conditions, the FAA aims to reduce the number of runway excursions.