PCN – Pavement Classification Number: A Comprehensive Guide

Introduction

The Pavement Classification Number (PCN) system is a cornerstone of modern airport operations, safety, and planning. It provides a standardized, easily interpretable means for airports worldwide to communicate the load-bearing strength of their pavements—runways, taxiways, and aprons—to all stakeholders, including engineers, pilots, airlines, and regulators.

The PCN system ensures that aircraft do not operate on pavements beyond their structural capacity, which would otherwise risk costly damage and compromise safety. Understanding PCN is essential for anyone involved in airport planning, operations, or aviation engineering.

What is PCN?

PCN (Pavement Classification Number) is an internationally recognized numerical value, coupled with a four-letter code, that describes the load-carrying capacity of an airport pavement. It enables direct comparison with an aircraft’s impact on that pavement (measured by the Aircraft Classification Number, or ACN), ensuring safe and efficient aircraft movements.

A typical PCN code looks like: 65/R/B/W/T. Each part provides crucial information:

• 65: Numerical strength value
• R: Rigid pavement (concrete)
• B: Medium subgrade strength
• W: No tire pressure limit
• T: Determined by technical evaluation

Historical Context and the Need for Standardization

Before PCN, pavement strength was reported as maximum allowable aircraft weights for specific landing gear types—a cumbersome system prone to misinterpretation, especially during international operations. The lack of a global standard led to confusion, operational inefficiencies, and safety risks.

The International Civil Aviation Organization (ICAO) addressed this by introducing the ACN-PCN system in 1981. The Federal Aviation Administration (FAA) and other authorities soon adopted it, codifying the methodology in ICAO Annex 14 and FAA Advisory Circular 150/5335-5C. Since then, the PCN system has become the global language for airport pavement strength.

The ACN-PCN System

Aircraft Classification Number (ACN)

The Aircraft Classification Number (ACN) quantifies the pavement-loading effect of a specific aircraft, taking into account its weight, landing gear configuration, tire pressure, and the type and strength of the pavement it uses. Each aircraft has multiple ACN values, depending on:

• Pavement type (flexible or rigid)
• Subgrade category (A–D)

If an aircraft’s ACN is less than or equal to the pavement’s PCN, and its tire pressure does not exceed the allowable limit, the aircraft may operate without restriction. Otherwise, operation is restricted or prohibited.

Aircraft manufacturers publish ACN values in flight and planning manuals, and regulatory authorities maintain ACN databases for operational use.

Pavement Types in PCN

Flexible Pavement (“F”)

Flexible pavements are typically constructed of asphalt, which distributes loads through a layered system. The load is spread laterally and diminishes in intensity with depth.

• Advantages: Lower construction costs, easier repairs, adaptability
• Weaknesses: More susceptible to rutting and deformation under heavy, repeated loads, especially with weak subgrades or high tire pressures

Rigid Pavement (“R”)

Rigid pavements consist of Portland cement concrete slabs, distributing loads mostly by slab bending.

• Advantages: High durability, better performance on poor subgrades, longer service life
• Weaknesses: Higher initial cost, more expensive and complex repairs, sensitive to subgrade irregularities

Subgrade Category (A–D)

The subgrade is the soil or base beneath the pavement. Its strength is crucial in determining pavement performance and is categorized as:

• A (High)
• B (Medium)
• C (Low)
• D (Ultra Low)

For flexible pavements, the California Bearing Ratio (CBR) is used; for rigid pavements, the modulus of subgrade reaction (k-value) is referenced.

• A: CBR ≥13, k ≥120 MN/m³
• B: CBR 8–13, k 60–120
• C: CBR 4–8, k 25–60
• D: CBR <4, k <25

Subgrade determination requires geotechnical investigation, often using techniques like dynamic cone penetrometer or plate load tests.

Allowable Tire Pressure (W, X, Y, Z)

Tire pressure influences pavement wear, especially for flexible surfaces. PCN codes include a tire pressure limit, categorized as:

• W: No pressure limit
• X: Up to 218 psi (1.5 MPa)
• Y: Up to 145 psi (1.0 MPa)
• Z: Up to 73 psi (0.5 MPa)

Exceeding the allowable tire pressure may cause rutting or surface damage, particularly on older or thinner flexible pavements.

Evaluation Methods: Technical (“T”) vs. Using Aircraft (“U”)

Technical Evaluation (T):

• Involves detailed engineering analysis using pavement design software (e.g., FAARFIELD, COMFAA)
• Considers pavement structure, materials, subgrade, and projected aircraft traffic
• Required for new construction and major rehabilitation
• Provides high accuracy and regulatory compliance

Using Aircraft Method (U):

• Based on operational experience with the heaviest aircraft using the pavement without causing visible distress
• Used when technical data is limited or unavailable
• Less precise; should be reviewed if aircraft mix changes

Five-Part PCN Code: Format and Interpretation

A complete PCN code looks like: 43/R/B/X/T

• 43: Numerical value (pavement strength; higher = stronger)
• R: Pavement type (R = rigid, F = flexible)
• B: Subgrade strength (A = high, B = medium, C = low, D = ultra-low)
• X: Allowable tire pressure (W, X, Y, Z)
• T: Evaluation method (T = technical, U = using aircraft)

This format allows for universal, unambiguous reporting and comparison.

How the ACN-PCN Comparison Works in Practice

Before authorizing an aircraft for a specific runway, taxiway, or apron, operators compare the aircraft’s ACN (for pavement type and subgrade category) to the published PCN:

• If ACN ≤ PCN: Operation without restriction
• If ACN > PCN: Operation may be restricted or require engineering analysis; risk of pavement damage increases

Exceeding PCN by more than 10% (flexible) or 5% (rigid) is generally not recommended without a special evaluation.

Subgrade Strength: CBR and k-Value in Detail

• CBR (California Bearing Ratio): Measures soil’s ability to bear load, used for flexible pavements.
• k-Value (Modulus of Subgrade Reaction): Measures stiffness of the supporting soil, used for rigid pavements.

Higher values mean stronger subgrades, requiring less pavement thickness for the same structural capacity.

Tire Pressure and Pavement Life

High tire pressures—common in modern jets—can cause significant stress and rapid wear on flexible pavements. This is why the PCN code’s tire pressure limit is critical in preventing rutting and surface failures, extending pavement life, and reducing maintenance costs.

PCN and Airport Infrastructure Planning

PCN values are fundamental for:

• Determining which aircraft can use which pavements
• Planning future expansions or upgrades
• Prioritizing maintenance and rehabilitation
• Regulatory compliance (FAA, ICAO)
• Investment justification and pavement management

PCN is published in FAA Form 5010 (USA) and Aeronautical Information Publications (AIPs) worldwide.

Determining PCN: Step-by-Step

1. Collect Pavement Data: Thickness, materials, condition
2. Subgrade Investigation: CBR or k-value testing
3. Aircraft Fleet Data: Weights, gear, tire pressure
4. Choose Evaluation Method: Technical (preferred) or Using Aircraft
5. Calculate PCN: With approved software or empirical data
6. Report and Publish: In all regulatory/operational documents
7. Review Regularly: Especially after repairs, upgrades, or changes in aircraft mix

Practical Example

Suppose a runway has a PCN of 50/F/B/X/T. A Boeing 737-800 has an ACN of 45 (for flexible, medium subgrade) and a tire pressure of 180 psi. Since ACN < PCN and tire pressure < 218 psi (category X), the aircraft can operate unrestricted.

Conversely, a heavier aircraft with an ACN of 60 would require special approval or risk damaging the pavement.

PCN in Regulatory Documents

• FAA Form 5010: US airports’ master record, including PCN values for all runways
• ICAO AIP: Aeronautical Information Publication, mandatory for all international airports
• Internal Pavement Management Systems: For ongoing tracking, maintenance, and planning

Advanced Topics: Overlay Design, Fatigue, and Life-Cycle

Overlay Design

Upgrading a pavement (overlay) often requires recalculating PCN to reflect the new structure. This is especially relevant as aircraft fleets evolve and pavement ages.

Fatigue Life and Cumulative Damage

PCN reflects a balance between safe operation and acceptable pavement life, factoring in cumulative load effects. Overloading accelerates fatigue and can force early, costly repairs.

The Future of PCN: Digital Management and Smart Airports

With the rise of digital pavement management systems, PCN values are now integrated into smart airport platforms. These systems use real-time data and predictive analytics to optimize pavement maintenance, update PCN values, and support sustainable airport growth.

Conclusion

The Pavement Classification Number (PCN) system is essential for safe, efficient, and sustainable airport operations worldwide. By providing a clear, standardized language for pavement strength, PCN enables airports to match infrastructure to the demands of modern aviation, protect investments, and ensure compliance with international standards. Whether you are an airport manager, engineer, pilot, or regulator, understanding and applying the PCN system is key to managing airport pavements with confidence.

Related Terms

• ACN (Aircraft Classification Number)
• Flexible Pavement
• Rigid Pavement
• Subgrade Category
• Tire Pressure
• Technical Evaluation
• Using Aircraft Method
• FAA Advisory Circular 150/5335-5C
• ICAO Annex 14

Further Reading

• ICAO Annex 14 – Aerodromes
• FAA Advisory Circular 150/5335-5C
• FAA Form 5010

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