# 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 apron (or ramp). This helps to ensure that the airport runway, taxiway, and apron (or ramp) are not subjected to excessive wear and tear, thus prolonging the usable life of the runway while promoting safe operations of the aircraft landing thereon.

## 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 the PCN numerical value, indicating the load-carrying capacity of the pavement. This is always reported as a whole number, rounded from the determined capacity. The value is calculated based on a number of factors, such as aircraft geometry and a pavement's traffic patterns, and is not necessarily the direct bearing 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 (most typically concrete) or a flexible (most typically asphalt) design.

The third part is another letter from A to D expressing the strength of what is underneath the pavement section, known as the subgrade. So a subgrade of A would be very strong, like concrete-stabilised clay. A subgrade of D would be very weak, like uncompacted soil.

Flexible pavements The flexible pavements have four subgrade categories as given below:

Category Strength Value
HIGH A CBR 15 (All CBR above 13%)
Medium B CBR 10 (For CBR between 8% to 13%)
Low Strength C CBR 6 (For CBR between 4% to 8%)
Ultra Low D CBR 3 (For CBR below 4%)

Rigid pavements The rigid pavements have four subgrade categories as given below:

Category Strength Value
HIGH A k = 150 MN/m² (550 lb/in²) (All k values above 120 MN/m²)
Medium B k = 80 MN/m² (300 lb/in²) (For values between 60 and 120 MN/m²)
Low Strength C k = 40 MN/m² (150 lb/in²) (For values between 25 and 60 MN/m²)
Ultra Low D k = 20 MN/m² (75 lb/in²) (All k values below 25 MN/m²)

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. Concrete surfaces can support tire pressures greater than those of existing commercial aircraft and are therefore nearly always rated W. Other letter classifications are as follows:

Category Pavement class Maximum tire pressure
Unlimited W No Pressure Limit
High X 1.75 MPa (254 psi)
Medium Y 1.25 MPa (181 psi)
Low Z 0.5 MPa (72 psi)

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 pavement's value indicating load-carrying capacity is 80 (unitless), is rigid (and thus is likely concrete), is on a medium-strength subgrade, has no limit on tire pressure, and has been calculated through technical evaluation.