In an industry where safety is paramount, every potential risk must be closely monitored and mitigated. As a result of the aviation industry's newfound understanding of how surface conditions can impact upon the wheel-braking capability of aircraft, pavement engineering has become a high priority.
Reduction of braking capacity is especially severe during winter operations, when runways and taxiways are wet or icy, but there are many other factors that come into play.
"If there is any kind of contaminant, such as snow, ice or water, this can impact upon braking," explains Professor Susan Tighe of the University of Waterloo in Canada. "Although winter conditions are the most likely to result in contamination, heavy rain can also affect braking conditions. Rubber, too, can build up on the runway and must be removed periodically, while foreign object debris ingested into the aircraft pose similar problems. And if the pavement surface is disintegrating - through the spalling of concrete or the ravelling of asphalt surfaces - this will make braking more unpredictable as well."
Tighe is the Norman W McLeod chair in sustainable pavement engineering, and the Canada research chair in pavement and infrastructure management at the University of Waterloo, where she is also director of the Centre for Pavement and Transportation Technology (CPATT). Her 18-plus years of experience in pavement design and management make her uniquely aware of pavement-related safety risks, as well as the need to raise awareness among all stakeholders and others who play a part in ensuring safe ground operations.
"The International Civil Aviation Organization, Federal Aviation Administration, Transport Canada and other airport authorities regulate pavement performance at airports, and mandate regular and frequent testing of airfields to ensure safety," says Tighe. "The challenge lies in the ever-changing nature of runway conditions. It is difficult to make real-time surface condition information available to pilots, but there is now a concerted effort being made across the industry to keep them informed," says Tighe.
Airport pavement management system
The potential dangers of impaired braking response have made Tighe and others keenly aware of the importance of implementing an airport pavement management system (APMS), which assists decision-makers in developing economically viable ways to keep pavements in a serviceable condition.
In essence, an APMS provides a consistent, objective and systematic procedure for determining airfield priorities and drawing up pavement maintenance schedules. It also helps to allocate resources effectively. While on the one hand, it uses available data to provide specific recommendations about what action should be taken to ensure a pavement network remains at an acceptable level of service, on the other, it can also help to minimise pavement-related expenditure.
The cost factor is significant. Historically, most agencies that are responsible for managing airport pavements have made decisions about maintenance and rehabilitation (M&R) on the basis of their experience and the best-known engineering practices. Tighe points out, however, that since 1985 the number of agencies using APMS for the management of such a critical asset has grown dramatically. As it stands, around 84% of state aviation agencies in the US use APMS, not least because US law states that an airport agency is only eligible for federal funding if it can show that it has an effective pavement maintenance management system in place.
Implementation of the APMS
The implementation of an APMS primarily involves identifying likely users and their needs, before selecting the appropriate software, conducting a pavement inventory, evaluating airfield conditions, and then customising the APMS system to analyse data and generate reports to suit those specific requirements.
Ensuring that implementation succeeds depends a great deal on providing adequate training and maintaining an up-to-date database of assets and their condition. This requires buy-in from all levels of management and the commitment of sufficient resources. To have long-term value, an APMS must adapt to any changes, such as airport expansion, and this requires investment.
Airport operators and airlines face the challenge of ensuring that limited financial resources are properly allocated to cover what is often a growing backlog of pavement rehabilitation needs. By implementing an APMS, these stakeholders will have the right tools at their disposal to determine their pavement needs, optimise the selection of M&R projects and evaluate the long-term impacts of these projects.
Monitoring pavement conditions
An APMS can go a long way towards ensuring that pavements are maintained in the best possible condition, but technology can also help to address problems that arise when surface conditions change. The key focus is on monitoring and measuring processes.
"While at the moment friction is a primary measure, here at the University of Waterloo we are currently working on a very important new device in partnership with Team Eagle," says Tighe. "It is key to have real-time data, particularly in such a dynamic environment. Also, with larger planes and heavier aircraft, this is essential to providing durable surfaces."
The work to which Tighe refers is intended to answer a significant question: what observable and measurable runway conditions can be communicated to aviators so that they can safely and accurately predict wheel-braking, aborted take-off and landing stopping distances?
The answer depends upon collecting the right data and using that data in real time to accurately reflect the situation on the ground. Partners including Team Eagle, Waterloo International Airport, WestJet and aircraft anti-skid braking system expert Arnie Beck have been working on the braking availability tester (BAT) to find the answers.
Cutting-edge brake testing
The BAT is a measurement mechanism that emulates the braking system of an aircraft on contaminated surfaces to provide predictive braking availability, which in turn can determine if aircraft can safely land or take off from a contaminated runway. It is not the same as a friction tester; rather it is a system that can be challenged to see how plane anti-skid braking systems react when braking aggressively in deformable contaminants.
"This is one way of trying to improve modern-day practice by developing a state-of-the-art device that combines measuring the pavement surface under the contaminant with that above it, considering that the braking availability with aircraft anti-skid braking systems often takes place within the deformable contamination itself - above the surface," Tighe says. "Civil engineers try to design the pavement surfaces so they are durable - ensuring they last a long time with minimal distress - and exhibit high friction.
"In the future," she concludes. "I believe that we need to provide real-time data wherever possible and invest enough money in our pavement surfaces to maintain them at a high level of service. This should be facilitated through proper pavement management to ensure that we design, construct and maintain surfaces that accommodate all traffic and weather conditions."