We Need to Do Better About the Top 6 mm

Alex Sydney
October
2022

Managing airfield pavement is a massive task, and the pandemic has made it more difficult. As airports lose employees, there are too few people managing maintenance, let alone looking to the future. As long-term employees leave, their experience monitoring the airfield is lost, and new employees do not have the intrinsic knowledge required to assess airfield safety as effectively.

One area often overlooked is, in some ways, the most important: the top 6 mm of runways. Guidance from FAA circulars and ICAO is outdated and does not reflect important improvements in technology and pavement engineering. Further, some airports build robust friction management programs, while others never measure friction.


Alex Sydney has worked at Halliday Technologies since 2011, where she developed the airport market for the RT3 Flight friction equipment. Sydney performs several roles in the company but especially enjoys working closely with customers to help them use friction data to make informed decisions about their surfaces. She has an MBA from The Ohio State University and has worked in customer-focused positions in several industries.

The concept is complicated. Friction is about how tires engage with the pavement. Surface contaminants vary, and no two surfaces are the same. We know concrete performs differently from asphalt and can vary based on where the aggregate was mined, how wet the material was when it was placed, and surface texture. Further, low-cost bidder requirements drive decisions that sometimes impede airports from selecting the highest quality installer.

I have heard scenarios where half of a runway shredded aircraft tires because the macro texture was too sharp, while the other half (laid by a different contractor) was fine. I have personally seen more than one new runway with significantly lower friction than the replaced runway because the macro texture was too smooth—likely because the mix was too wet. I have encountered asphalt runways glued together with crack-seal products, and other runways with many different surface textures because sections were replaced at different times. All these factors impact friction and therefore safety.

After pavement installation, surface friction may improve in the first few years as the aggregate is exposed to environmental conditions. But pavement also deteriorates from aircraft landings, how aircraft exit runways and routine maintenance. Importantly, pavement deterioration is not linear. Once it begins, it accelerates.

In short, airfield surfaces are dynamic, and we need to monitor pavement changes carefully so we can anticipate failure. I often hear, “This pavement is only 10 years old, so it should be ok.” Or “This pavement is 15 years old and should be replaced.” But why are we making decisions based on age? Decisions should be based on performance and detailed, objective data.

There are abundant choices for friction testing equipment. However, testers from different manufacturers do not measure identically. Each airport must determine which equipment will give it reliable, repeatable and precise results over time, so personnel can see trends in the data. They also need to combine friction data with visual observations to understand how the surface generates those values.

I often get quizzical looks when I walk a runway, take photos of macro and micro textures, touch the surface and take notes. This process allows me to relate visual observations with friction data to guide decisions about cleaning, remediation or replacement.

To maximize return on investment, airports must use a performance-driven understanding of their surfaces. That means measuring friction, observing changes in the pavement and identifying deterioration before replacement is needed. This approach should not be limited to Class 1 airports with money for friction testers. Airports with smaller budgets should share equipment.

Those in the industry who focus on the top 6 mm of pavement should encourage the use of quality equipment that provides reliable friction results. We should create tools that help airport employees synthesize data easily, quickly identify problem areas and incorporate their knowledge into decisions. That way, knowledge is not lost when employees leave the airport.

Pavement engineers, equipment manufacturers, materials companies and regulatory groups need to improve their understanding of how changes to pavement surfaces impact tire performance. We must encourage practical research so lessons learned are implementable. And we must identify best practices for pavement-surface management, based on the number and type of planes landing and local environmental conditions.

The industry needs to create a repository of documents that “normal people” can understand, with best practices about the latest insights. Airport operators do not want to read technical documents filled with calculations; they want to know how to interpret friction results and pavement observations to make good decisions about their airfields.

As an industry, we need to do a better job helping airport operators successfully manage their pavements. We each need to play our part in understanding the top 6 mm of pavement and make decisions that will increase safety, maximize performance and optimize spending.

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