Evaluation of Unsurfaced Airfield Criteria for Operation of C-17 Aircraft

To determine the impact of C-17 aircraft on unsurfaced airfields, the U.S. Army Engineer Waterways Experiment Station was asked to construct full-scale pavement section items and traffic them to failure with a fully loaded C-17 aircraft main gear assembly (six wheels). The extrapolation of existing criteria used on two and four wheel aircraft gear studies was suspect, particularly when considering the configuration of the C-17 aircraft main gear. Three strengths of surfacing material (6, 9, and 12 California Bearing Ratio) were used to evaluate the current criteria. The results of full-scale pavement trafficking indicate that current criteria should be considered appropriate for use as a tool in designing/evaluating the expected performance of unsurfaced airfields for operations of C-17 aircraft. It should be noted that surface shearing occurred in the landing/braking zone on unsurfaced airfields during flight tests in 1997. The criteria addressed in this paper does not consider the rutting caused by braking shear.