There has been a need for a more descriptive explanation of concrete rigid pavement design charts as used in the Airplane Characteristics for Airport Planning document. Lockheed has made certain modifications to the published Portland Cement Association (PCA) computer program which assisted in preparation of the charts. This explanation will permit one to better understand the development and use of the charts for the design and evaluation of airfield pavements as well as of the use of the program for landing gear design.