Since the advent of turbojet aircraft with their greater weight and high landing speeds, braking performance on runway surfaces, particularly when wet, has become a significant safety consideration.
Pavement Maintenance and Evaluation Research
Regardless of pavement type or surface treatment, runway friction characteristics will change over time depending on type and frequency of aircraft activity, weather, environmental issues, and other factors. In addition to ordinary mechanical wear and tear from aircraft tires, contaminants can collect on runway pavement surfaces to decrease their friction properties. Contaminants such as rubber deposits, dust particles, jet fuel, oil spillage, water, snow, ice, and slush all cause friction loss on runway pavement surfaces. Rubber deposits occur in the touchdown areas on runways and can be quite extensive. Heavy rubber deposits can completely cover the pavement surface texture thereby causing loss of aircraft braking capability and directional control when runways are wet.
Scheduling Pavement Evaluations
The operator of any airport with significant jet aircraft traffic should schedule periodic friction evaluations of each runway that accommodates jet aircraft. These evaluations should be carried out in accordance with the procedures outlined in either Section 2 or 3 of this chapter, depending upon the availability to the airport operator of continuous friction measuring equipment (CFME). Every runway for jet aircraft should be evaluated at least once each year. Depending on the volume and type (weight) of traffic on the runways, evaluations will be needed more frequently, with the most heavily used runways needing evaluation as often as weekly, as rubber deposits build up.
|Minimum Friction Survey Frequency
The table on the right should be used as guidance for scheduling runway friction surveys. This table is based on an average mix of turbojet aircraft operating on any particular runway.Surveys Without CFME
Research has shown that visual evaluations of pavement friction are not reliable. All airports with turbojet traffic should own or have access to use of CFME.
The Federal Aviation Administration (FAA) and National Transportation Safety Board (NTSB) have recognized the potential danger associated with poor runway surface conditions. FAA Advisory Circular 150/5320-12C (PDF 2.9M) requires runway friction testing at all U.S. carrier airports. FAA Inspectors are mandated to close runways and deny certification of airports when runway friction measurements are below recognized safe minimums.