1. Monty Wade, P.E Applied Pavement Technology, Inc. April 4, 2012
Do You Know Your PCN?
Monty Wade, P.E
Applied Pavement Technology, Inc.
April 4, 2012

2. Overview ACN-PCN definitions and concept History of ACN-PCN procedure
ICAO methodology
FAA Advisory Circular 150/5335-5B
COMFAA program and support spreadsheet
Interpretation of results

3. ACN-PCN Definitions
Aircraft Classification Number (ACN) – single unique number to express effect of an individual airplane on different pavements
Pavement Classification Number (PCN) – single unique number to express the load-carrying capacity of a pavement, without specifying a particular airplane or pavement structure

4. Concept of ACN-PCN System
A pavement with a given PCN can support, without weight restriction, an aircraft with an ACN rating equal to or less than the pavement PCN.

5. Session 11. ACN-PCN Procedure
ACN-PCN Background
Established by International Civil Aviation Organization (ICAO) in 1981
Presented in Aerodrome Design Manual, Part 3: Pavements
FAA developed a procedure to determine PCN in compliance with ICAO standards
FAA moving toward use of PCN in lieu of using allowable loads by gear type
Airport Consultants Council

6. Why ACN-PCN?
United States is a member of the International Civil Aviation Organization (ICAO) and is bound by treaty agreements to comply with their requirements to the maximum extent practical
FAA Order , FAA Rulemaking Policies, Chapter 11

7. FAA Guidance on ACN-PCN
Session 11. ACN-PCN Procedure
FAA Guidance on ACN-PCN
AC 150/5335-5B, Standardized Method of Reporting Airport Pavement Strength – PCN
Supporting software (COMFAA 3.0) and support spreadsheet
AC and COMFAA released on August 26, 2011
Support spreadsheet revised on February 12, 2102
PCN field has been added to FAA Form 5010
Airport Consultants Council

8. AC 150/5335-5B Requirements
Effective three years after the issue date of this AC, all public-use paved runways at primary airports serving air carrier aircraft should be assigned gross weight and PCN data using the guidance provided in this AC. Effective five years after the issue date of this AC, all public-use paved runways at nonprimary commercial service airports serving air carrier aircraft should be assigned gross weight and PCN data using the guidance provided in this AC.

9. AC 150/5335-5B Requirements
The FAA recommends the guidelines and specifications in this AC for reporting airport pavement strength using the standardized method. In general, use of this AC is not mandatory. However, use of this AC is mandatory for all projects funded with Federal grant monies through the Airport Improvement Program (AIP) and with revenue from the Passenger Facility Charge (PFC) Program. See Grant Assurance No. 34, “Policies, Standards, and Specifications,” and PFC Assurance No. 9, “Standards and Specifications.”

10. ACN Computation
Ratio of a computed single-wheel load to a reference single-wheel load
Flexible Pavements
Based on the USACOE ESWL CBR method
Alpha factors adopted by ICAO October 2007
Thickness is computed for 10,000 coverages
Rigid Pavements:
Based on PCA Westergaard interior stress method
These are fixed standard procedures. Other design procedures or traffic levels cannot be substituted.

11. Subgrade Strength for ACN
Session 11. ACN-PCN Procedure
Subgrade Strength for ACN
Flexible Pavements
CBR of the subgrade soil
Rigid Pavements
k-value at the top of the support
Includes all base/subbase layers
Don’t use k-value of subgrade soil
Airport Consultants Council

12. Official ACN Official ACNs are provided by the Aircraft Manufacturer
Also reports center of gravity, maximum gross load, and tire pressure used in calculation
Published by manufacturer in Airplane Characteristics for Airport Planning
Can be determined using FAA’s COMFAA 3.0 program

13. PCN Reporting Information
PCN values are reported in a coded format using 5 parts separated by “/”
Sample: 39/F/B/X/T
Information includes:
Numerical PCN Value = 39
Pavement Type = F (Flexible)
Subgrade Category = B (CBR of 10)
Allowable Tire Pressure = X (< 218 psi)
Evaluation Method = T (Technical Method)

14. Subgrade Categories for Rigid Pavement
Four subgrade strengths:

15. Subgrade Categories for Flexible Pavement
Four subgrade strengths:

16. Tire Pressure Categories
Four tire pressure categories:
Rigid pavements can typically be rated as W
In general, flexible pavements with 4 to 5 inches of well-placed HMA can generally be rated with code X or W, while thinner pavement of poorer quality asphalt should not be rated above code Y

17. Evaluation Method
Using Aircraft Method
Technical Evaluation Method

18. Session 11. ACN-PCN Procedure
Using Aircraft Method
Select the highest ACN of all aircraft regularly using the pavement to be the PCN
ICAO manual: “Support of a particularly heavy load, but only rarely, does not necessarily establish a capability to support equivalent loads on a regular repetitive basis”
This method is discouraged because of potential of over-estimating or under-estimating pavement capacity
Airport Consultants Council

19. Technical Evaluation Method
The ICAO manual covers in detail a very broad range of methods, including:
Any rational design procedure developed specifically for airport pavements but applied in reverse for pavement evaluation
Pavement surface deflection measured under the load from a representative aircraft
Non-destructive test results with backcalculation
Allows for design and evaluation procedures not in use when the manual was written
FAA procedure is an acceptable “technical evaluation” method

20. AC 150/5335-5B Approach Design approaches in new Advisory Circular:
Flexible pavements: ESWL CBR method
Rigid pavements: Westergaard’s edge stress as implemented in AC 150/5320-6C and -6D; PCA center stress method can also be selected in COMFAA 3.0
Selected for backward compatibility with established methods and compatibility with the ACN computation procedure

21. Primary Changes for -5B
The procedure for selecting the critical aircraft has been substantially revised: evaluates all aircraft opposed to single critical aircraft
The procedure for computing equivalent departures has been replaced with a procedure based on cumulative damage factor (CDF)
Procedure has been completely automated in COMFAA 3.0
A spreadsheet application has been developed to facilitate the evaluation and interpretation

22. Session 11. ACN-PCN Procedure
Traffic for PCN
20-year traffic from time of analysis
Generally based on aircraft departures
Pass/Coverage (P/C) – number of aircraft passes to fully load a unique point in the pavement
Traffic Cycle (TC) – complete cycle of an aircraft, including a landing pass, a takeoff pass, and associated taxi
Pass/Traffic Cycle (P/TC) – number of passes in a complete traffic cycle, which is based on:
Refueling operations (arrival vs. departure weights)
Runway/taxiway configuration
Airport Consultants Council

23. Overload Guidance Flexible pavement
ACN should not exceed 10% of the reported PCN
Rigid pavement
ACN should not exceed 5% of the reported PCN
Annual overload movements should not exceed ~5% of total annual aircraft movements

24. Overload Guidance
Occasional overloads should not adversely affect the pavement
Overloads should not be allowed:
If pavement is exhibiting signs of distress
During periods of thaw
When pavement/subgrade is weakened by water
Monitor pavement condition regularly

25. Uses of ACN-PCN System
Determine if pavement can support current or projected aircraft mix
Determine if a certain aircraft can land at your airport (once, regular, unlimited)
Determine allowable weight of an aircraft for a specified number of operations
Assess whether an aircraft will damage the pavement (remaining life)
Not a pavement design procedure (but recommend checking during design phase)

26. Session 11. ACN-PCN Procedure
PCN Batch Mode
Airport Consultants Council

27. Additional Computational Modes
Session 11. ACN-PCN Procedure
Additional Computational Modes
Airport Consultants Council

28. COMFAA Support Spreadsheet
Equivalent thickness for flexible pavement:
Effective “top-of-base” k-value for rigid pavement
Flexible and rigid PCN summary and charts (data parsing and interpretation)
Form 5010 elements
Revised on February 12, 2012

29. Session 11. ACN-PCN Procedure
Flexible Pavements
Airport Consultants Council

30. Rigid Pavements

31. Processing COMFAA Output

32. Processing COMFAA Output

33. Form 5010 Elements

34. Interpretation of Results
Session 11. ACN-PCN Procedure
Interpretation of Results
Airport Consultants Council

35. Interpretation of Results
Session 11. ACN-PCN Procedure
Interpretation of Results
Airport Consultants Council

36. What is the PCN of this facility with multiple sections?
Session 11. ACN-PCN Procedure
What is the PCN of this facility with multiple sections?
A runway consists of four sections
Determined PCNs are:
Section 1: 64/F/A/W/T
Section 2: 106/F/A/W/T
Section 3: 82/F/A/W/T
Section 4: 66/F/A/W/T
What PCN should be reported?
Airport Consultants Council

37. Can aircraft X land at this airport?
Session 11. ACN-PCN Procedure
Can aircraft X land at this airport?
Aircraft X wants to use the runway in the previous example
Aircraft X has an ACN of 68
Should the aircraft be allowed to use the runway?
Airport Consultants Council

38. Additional Notes
PCNs depend on the traffic mix used to determine them; need to re-evaluate posted PCN if significant changes to the original traffic mix occur
Recommend determining PCN during design
Analysis of composite pavements; can be considered flexible pavement when HMA thickness is 75 to 100 percent of PCC thickness

39. ACC Training Airport Pavement Design and Evaluation Workshop
2.5-day training session (1/2 day on PCN)
Presentation and discussion
Workshop problems
Typically taught twice per year
PCN Webinar
90-mintue session
Coming soon

40. Summary ACN-PCN definitions and concept History of ACN-PCN procedure
ICAO methodology
FAA Advisory Circular 150/5335-5B
COMFAA program and support spreadsheet
Interpretation of results