Computation of Aircraft Braking Distances

Wet runways are known to be a major contributing factor in overrun accidents. Studies have shown that low skid resistance caused by reduced friction on wet pavement leads to a longer braking distance and increases aircraft overrun risk. The common approaches to compute aircraft braking distance and overrun risk are based on either statistical predictive equations derived from accident data or analytical methods using estimated ground friction values. Both approaches are unable to calculate aircraft braking distance accurately because they cannot account for the complex relationship between wet-pavement skid resistance and the highly varied aircraft operating conditions (which are characterized by factors such as aircraft tire type, landing speed, wheel load, tire inflation pressure, and thickness of runway surface water film). To overcome this limitation, an improved procedure for calculating wet-pavement braking distance based on engineering mechanics and fluid dynamics theory is proposed. An analytical simulation model is first developed to evaluate the wet-pavement skid resistance available to an aircraft under a given operating condition, which is defined by aircraft speed, tire structural properties, pavement surface properties, wheel load, tire inflation pressure, and pavement surface water-film thickness. With actual measured data reported in the literature, a numerical example is presented to demonstrate the application of the proposed procedure. The example illustrates the calibration and validation of the tire model, followed by computation of braking distances under different operating conditions of wheel load, tire inflation pressure, landing speed, and water-film thickness.