Pavement Classification Number
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The Pavement Classification Number (PCN) is an International Civil Aviation Organization standard used in combination with the Aircraft Classification Number (ACN) to indicate the strength of a runway, taxiway or airport ramp (or apron). This helps to ensure that the airport ramp is not subjected to excessive wear and tear and thus lengthen its life.
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[edit] Usage
Although important for the runway the major use of this number is for the apron. On landing the aircraft is light on fuel and usually less than 50% of the weight of the aircraft touches the runway in one go. On takeoff the aircraft is heavy but as the aircraft accelerates the weight gradually moves from the wheels to the wings. It is while the aircraft is being loaded and taxiing prior to departure, that the apron experiences significant loads from aircraft weight.
Typically this is only used for asphalt or concrete runways and would not be used for grass or gravel.
[edit] How it Works
The PCN is actually expressed as a five part code, separated by forward-slashes, describing the piece of pavement concerned.
The first part is a numeric value expressing the actual assessed strength of the pavement. The second part is a letter: either an R or an F, depending on whether the pavement itself is of a rigid or a flexible design.
The third part is another letter from A to D expressing the strength of what is underneath the pavement, known as the subgrade. So a subgrade of A would be very strong, most likely a reinforced concrete subbase. A subgrade of D would be very weak, most likely uncompacted soil.
The fourth part is either a letter, or a number with units expressing the maximum tire pressure that the pavement can support. In terms of letters, W is the highest, indicating that the pavement can support tires of any pressure, the others are as follows:
| Pavement Class | Maximum Tire Pressure (psi) |
|---|---|
| X | 217 |
| Y | 145 |
| Z | 73 |
The fifth and final part just describes how the first value was worked out, a T indicates technical evaluation, and a U indicates usage -- a physical testing regime.
So a PCN of 80/R/B/W/T means that the underlying (probably asphalt) has a bearing strength of 80, is rigid, it's on a medium subgrade, it can withstand a tire pressure of 217 psi, and this has been calculated through technical evaluation.
