Recalibration of Airport Pavement Structural Design System

Aircraft pavement thickness design remains tied to empirical relationships derived from full scale test data. With the introduction of the six wheel landing gears of the A380 and B777 the current failure criteria for the Australian developed pavement design program Aircraft Pavement Structural Design System (APSDS) were no longer valid. APSDS was recently recalibrated using a greater number of aircraft at different masses and a greater range of aircraft coverages than were used initially. The S77-1 pavement thicknesses against which the calibration was performed were generated using the replacement Alpha Factor values endorsed by the International Civil Aviation Organization (ICAO) in October 2007. Replacement values of the calibration constants have now been developed for the following three situations: 1. A single failure criterion over all subgrade California Bearing Ratios (CBRs) and wheel configurations. 2. A criterion for each value of CBR but combining all wheel configurations. 3. A criterion for each subgrade CBR and for each wheel configuration (1, 2, 4 and 6-wheel). The second scenario produced significant improvement in the agreement between S77-1 and APSDS pavement thicknesses when compared to that provided by the current calibration constants. By considering each aircraft wheel configuration separately, a more significant improvement was achieved. Combining all wheel configurations and subgrade CBRs into a single failure criterion provided the least improvement to the current APSDS calibration. The influence of subgrade CBR and aircraft wheel configuration were found to be significant and separate failure criteria should be adopted for each subgrade and each wheel configuration. This finding contrasts with the approach by the FAA in LEDFAA 1.3. LEDFAA 1.3 adopts a single failure criterion for all CBRs and all wheel configurations.