Because ICAO lays down the method of determining ACN for both flexible and rigid pavements, this step has been achieved easily. NATO has published individual ACN values for the range of aircraft likely to use its airfields in Standard NATO Agreement 7131 ACN-PCN and Allied Engineering Publication 46a. NATO’s has replaced the older Load Classification (LCN) system in NATO Criteria and Standards for Airfields with ACN.

The February 2003 ASWG meeting decided to let nations use their own national design theories to determine PCN. An inquiry of the U.S. Corps amongst several nations learned that the pavement design method used by individual nations lead to different pavement thickness (and PCNs). Consequently, different nations get different results. This, and the fact that the PCN reporting system does not reflect the actual pavement life are considered as shortfalls of the ACN-PCN system. Therefore additional information such as the number of aircraft passes used to make the calculation must be provided (runway only). Nations shall provide the following information:

• Airfield name, runway(s) and PCN value(s);
• Type of aircraft for which the PCN values are based;
• Number of aircraft passes used to make the calculation.

The additional information allows NATO to compare NATO airfield strength values as required and shown in the previous table.

A small group of national pavement experts of several NATO nations meet each other on a regular basis to discuss pavement topics. Items such as bearing capacity (STANAG 7131 Ed1; AEP-46A ACN/PCN), runway friction and braking conditions (STANAG 3634 Ed4) and visual inspections and pavement management (AEP-56) are discussed for broad usage within NATO nations.

With the current world situation, there is an increasing need for NATO standards with respect to airfield pavement design to support joint military operations. It is critical to mission planners that methods steps are taken to insure that global methods for reporting the structural capacity of an airfield are available. Several Nations have implemented mechanistic design/evaluation systems with criteria that appear to be yielding reasonable results. Many of these procedures are based on linear, elastic theory coupled with empirical relationships for relating computed stress/strain to allowable aircraft load. This approach is well understood and well documented. The elastic layer mechanistic/empirical methods are also very adaptable to new criteria. For example, it is not very difficult to add/remove/modify the criteria (fatigue relationships). This makes it attractive since results from continuing research and development could be incorporated as necessary. With the current emphasis and requirements for better design/evaluation methods, a NATO standard could be established that would be well accepted among the Nations.