The ranges of subgrade strength covered by these standard subgrade categories (designated as A, B, C and D) are shown below.

The ICAO "Aerodrome Design Manual - Part 3 - Appendix 2" contains computer programs (source code) for the calculation of ICAO ACN's for aircraft operation on both rigid and flexible pavements. The ICAO ACN Fortran source code has been rewritten and recompiled by Transport Canada into two (2) executable stand-alone programs. The original input/output formats of the ICAO ACN programs were followed as closely as possible. The internal program calculations and equations of the ICAO programs were also followed and incorporated in the new .exe files. The result is the computation of aircraft ACN values that are fully compatible with the ICAO ACN/PCN strength reporting system for airfield pavements. The programs are available at http://www.tc.gc.ca/CivilAviation/.../software.htm