Maximizing throughput at soft airfields

Aircraft operations on soft fields are limited due to field rutting. Each subsequent aircraft pass, defined as one takeoff and one landing, increases field rutting until the field reaches a point where further aircraft operations are no longer permissible. The ability of aircraft to operate on soft fields is often expressed as a function of aircraft landing weight and the California Bearing Ratio (CBR) of the field (which measures the ability of the soil to resist compressive loads). Because soft fields can support only a limited number of takeoffs and landings, it is important to understand how to maximize the cargo throughput at these soft fields. The calculations in this document show that there exists an optimum landing weight that allows for maximum cargo delivery. This optimum landing weight is constant and independent of both aircraft ramp weight and field CBR. There is also is a maximum landing weight at which a given cargo requirement can be met. The author illustrates these calculations using the C-17A, which is one of the options being considered in the joint future theater airlift analysis of alternatives.