ACN-PCN method
index of the relative effect of an aircraft on a specific runway
The Aircraft Classification Number (ACN) – Pavement Classification Number (PCN) method is a standardized international airport pavement rating system promulgated by the ICAO in 1981. The method has been the official ICAO pavement rating system for pavements intended for aircraft of apron (ramp) mass greater than 5700 kg from 1981 to 2020. The method is scheduled to be replaced by the ACR-PCR method by November 28, 2024.
For the safe and efficient use of pavements, the method has been designed to:
enable aircraft operators to determine the permissible operating weights for their aircraft;
assist aircraft manufacturers to ensure compatibility between airfield pavements and the aircraft under development;
permit airport authorities to report on the aircraft they can accept and allow them to use any evaluation procedure of their choice to ascertain the loading the pavements can accept.
The method relies on the plain comparison of two numbers:
The ACN, a number that expresses the relative effect on an airplane of a given weight on a pavement structure for a specified standard subgrade strength;
The PCN, a number (and series of letters) representing the pavement bearing strength (on the same scale as ACN) of a given pavement section (runway, taxiway, apron) for unrestricted operations.
Aircraft Classification Number (ACN)
The ACN calculation process is fully described in ICAO Doc 9157 Aerodrome Design Manual – Part 3 "Pavements" (2nd ed.).
The procedure to calculate the ACN is as such:
Design a theoretical pavement according to a defined criterion:
For flexible pavements, design the pavement for 10,000 load applications of the aircraft according to the CBR design procedure combined with Boussinesq's solution for deflection in the elastic half-space
For rigid pavements, design the pavement to reach a standard flexural stress of 2.75 MPa at the bottom of the cement concrete layer according to Westergaard theory
Calculate the single wheel load, inflated at 1.25 MPa, that would require the same pavement – this is the Derived Single Wheel Load (DSWL)
The ACN is defined as twice the DSWL, expressed in thousands of kilograms
The ACN are calculated for four standard subgrade strengths, for flexible and rigid pavements, thus leading to 8 different values.
ACNs depend on the landing gear geometry (number of wheels and wheel spacing), the landing gear load (that is dependent upon the aircraft weight and center of gravity) and the tire pressure.
Normally, the aftmost center of gravity for the Maximum Ramp Weight (MRW) lead to the critical ACN.
Aircraft manufacturers publish the ACNs of their aircraft in their respective Aircraft Characteristics manuals.
The ICAO Aerodrome Design Manual contains the source code of computer programs for the calculation of ACNs.
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