States are required to evaluate and publish the strength of airport pavements using ICAOs ACN-PCN system. The method concentrates on classifying the relative damage of aircraft. ICAO foresees that each pavement authority will define a Pavement Classification Number (PCN) by whatever means is considered suitable to indicate the support level of a particular pavement such that all aircraft with a published ACN equal to or less than the reported PCN can use that pavement safely, without load bearing failure or undue damage to the structure.

The ACN-PCN system provides a standardised international airplane/pavement rating system replacing the various S, T, TT, LCN, AUW, ISWL, etc., rating systems throughout the world. In 1981 ICAO promulgated the ACN/PCN method as the single universal system for determining the weight limitation of aircraft operating on airport pavements by a procedure of comparing an airport’s Pavement Classification Number (PCN) with an Aircraft Classification Number (ACN). To avoid accelerated deterioration and excessive maintenance costs and for the safeguarding of pavement integrity and assurance of optimum service life ICAO utilises the ACN /PCN load classification method for reporting pavement strength. According to this world-wide standard, aircraft can safely operate on a pavement if their ACN is less than or equal to the pavement load bearing capacity or PCN. An aircraft having an ACN equal to or less than the PCN can operate without weight restrictions on a pavement.

It must be noted that the ACN/PCN method is not a design or evaluation method, but purely a classification system. Unfortunately the fact that the method of calculating ACN utilises two common design and analysis methods (the CBR equation and Westergaard theories) has led a surprisingly large number of people to assume that it is a design and evaluation method. It is not uncommon for reference to be made to PCN’s calculated by the ACN/PCN method. In fact the ICAO documentation makes it very clear that it is not a design/evaluation method and that the PCN is simply the ACN of the most damaging aircraft that can use the pavement on a regular basis (regular being defined by the operator).

The ACN/PCN method only deals with aircraft weighting in excess of 5.700 kg ( 12,566 lb.) as the airports with pavement for smaller size aircraft need only report the maximum allowable mass and the maximum allowable tire pressure if applicable. The ACN/PCN system ensures that both aircraft and pavement can be utilised to their maxi-mum extend without detrimental effects. According to the Design Manual the method is meant only for publication of pavement strength data in the Aeronautical Information Publication (AIPs). It is not intended for design or evaluation of pavements, nor does it contemplate the use of a specific method by the airport authority either for the design or evaluation of pavements. Although the Design Manual states that any method may be used to determine the load rating of the pavements, it is obvious that the use of layered elastic method in conjunction with calibrated failure criteria is preferred.