A method for developing preliminary friction deterioration model on runway

A deterioration model of friction was set up by analyzing the lateral variability of a runway in a regional airport. Airfield runways must provide adequate skid resistance to give the rotation to the wheels, and to ensure the directional control and the safe braking of aircraft operating on the surface. The degree of skid resistance provided by a pavement is expressed in terms of the surface "Coefficient of Friction" (COF) which is simply defined as the ratio of the measured horizontal force (braking) to the vertical one (loading) acting on a test wheel, braked to give a predefined percentage of slip, as the wheel passes over the surface. Runway friction testing is usually performed by making four test runs along the length of the runway (two on each side of centreline every 3 metres). Through this procedure, areas of low friction could not be identified and the required maintenance actions not programmed. As a matter of fact, runway friction deteriorates with the coverages, which represent the number of times when a particular point on the pavement is expected to be stressed as a result of aircraft operations. Coverages are function of aircraft type (configuration of the landing gear: wheelbase of main gear, number and spacing of wheels), the width of tire-contact area, and the lateral distribution of the aircraft wheel-path relative to the guideline marking (pavement centreline). In this study an experimental analysis was carried out on the regional airport of Rome Ciampino, in order to evaluate the longitudinal and crosswise variability of friction on the runway. The friction tests were made by equipment Adhéra of LPC on about 40 traces (or profiles) every 20 m (i.e. about 3400 friction tests) and a friction map of the runway was developed. The analysis showed a significant lateral, as well as longitudinal, variability of friction, and it suggested that a subdivision of the runway in homogeneous areas should be made (e.g. central touchdown area, lateral touchdown area, etc). Moreover, a criteria for developing deterioration model through short term experimental measurements was illustrated. As a matter of fact, friction mapping was used to develop an empirical friction deterioration model by regression analysis, in which the friction values are function of number of coverages and contact pressure