¶ Introduction
The Aircraft Classification Number -- Pavement Classification Number (ACN-PCN) is a standardized method set by the ICAO to report airport runway, taxiway, and apron pavement strength. It is used to assess the operation conditions of an aircraft depending on its weight and on the strength of the pavements.
This information is published in a standardized format following the guidelines provided in the Annex 14 of ICAO Regulations.
¶ PCN: Pavement Classification Number
The PCN is a five-part code associated to any section of the airport pavements (runway, taxiways, aprons or ramps) and indicates its mechanical resistance with respect to excessive wear and tear.
Each part of the code is separated by a forward-slash.
- PCN numerical value: it indicates the load-carrying capacity of the pavement.
- First letter: it indicates the rigidity of the pavement
- R for rigid (most typically concrete)
- F for flexible (most typically asphalt)
- Second letter: it expresses the strength of what is underneath the pavement section, known as the subgrade
- A for high strength: characterized by K = 150 MN/m3 and representing all K values above 120 MN/m3 for rigid pavements, and by CBR = 15 and representing all CBR values above 13 for flexible pavements.
- B for medium strength: characterized by K = 80 MN/m3 and representing a range in K of 60 to 120 MN/m3 for rigid pavements, and by CBR = 10 and representing a range in CBR of 8 to 13 for flexible pavements.
- C for low strength: characterized by K = 40 MN/m3 and representing a range in K of 25 to 60 MN/m3 for rigid pavements, and by CBR = 6 and representing a range in CBR of 4 to 8 for flexible pavements.
- D for ultralow strength: characterized by K = 20 MN/m3 and representing all K values below 25 MN/m3 for rigid pavements, and by CBR = 3 and representing all CBR values below 4 for flexible pavements.
- Third letter: it expresses the maximum tire pressure that the pavement can support
- W: Unlimited: no pressure limit
- X: High: pressure limited to 1.75 MPa
- Y: Medium: pressure limited to 1.25 MPa
- Z: Low: pressure limited to 0.50 MPa
- Fourth letter: it describes how the PCN numerical value was determined
- T indicates technical evaluation
- U indicates usage -- a physical testing regime
Example 1. If the bearing strength of a rigid pavement, resting on a medium strength subgrade, has been assessed by technical evaluation to be PCN 80 and there is no tire pressure limitation, then the reported information would be:
PCN 80 / R / B / W / T
Example 2. If the bearing strength of a composite pavement, behaving like a flexible pavement and resting on a high strength subgrade, has been assessed by using aircraft experience to be PCN 50 and the maximum tire pressure allowable is 1.25 MPa, then the reported information would be:
PCN 50 / F / A / Y / U
Example 3.--- If the bearing strength of a flexible pavement, resting on a medium strength subgrade, has been assessed by technical evaluation to be PCN 40 and the maximum allowable tire pressure is 0.80 MPa, then the reported information would be:
PCN 40 / F / B / 0.80 MPa /T
PCN is normally published on charts.
¶ ACN: Aircraft Classification Number
The ACN is a single unique number that expresses the relative effect of an airplane of a given weight on a pavement structure for a specified standard subgrade strength.
The airplane manufacturer provides the official computation of a reference ACN value. Nevertheless, the computation of the actual ACN requires detailed information on the operational characteristics of the airplane such as maximum centre of gravity, maximum ramp weight, wheel spacing, tire pressure, and other factors.
A typical ACN for a given aircraft is normally provided as follows:
An exhaustive list of the ACN for most of the existing aircraft can be found in IVAO HQ documentation.
The actual ACN of a given aircraft of weight M and corresponding to a pavement with known characteristics can be calculated as follows:
Mmin is the Operating Empty Weight
Mmax is the Maximum Apron Weight
M is the landing Weight
ACNmin and ACNmax are the ACN corresponding to Mmin and Mmax respectively.
The calculated ACN is then compared to the PCN of the foreseen airport pavements to assess the feasibility of the aircraft manoeuvre and operations.
¶ Practice of ACN/PCN method
¶ General principle
An aircraft, characterized by its actual operating weight (at pushback, taxi, takeoff and landing), is authorized to operate and manoeuvre on a given airport zone (ramp, apron, taxiway, runway) depending on the comparison between its actual ACN and the published PCN of the concerned pavement.
If ACN < PCN the aircraft can manoeuvre without restrictions.
If ACN > PCN the aircraft can be accepted under specific limitations, concerning for example its maximum weight or the operation frequency.
The requirements imposed by the ACN/PCN method are essentially meant to preserve the quality of the airport pavements and improve their lifetime. This is the reason why operation under specific limitations is accepted since it does not affect the safety of aircraft and people.
¶ Tolerance of acceptation
Nevertheless, whenever the difference between the ACN and the PCN exceeds 10% for flexible pavements or 5% for rigid ones, specific
studies are carried out to assess the operation feasibility and associated maintenance over costs.
¶ Flowchart of the ACN/PCN method
The ANC/PCN method can be synthesized by the following algorithm that must be used step by step to evaluate the allowable load on the concerned pavement and compare it with the actual aircraft weight.
- none
- ICAO Documentation Annex 14 - Aerodromes - Volume I - Aerodrome Design and Operation - 8th Edition July 2018 - Chapter 2.6
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