Do You Know Your PCN?

1. 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. 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

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 2100.13, FAA Rulemaking Policies, Chapter 11

7. 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

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 • Thickness is computed for 10,000 coverages These are fixed standard procedures. Other design procedures or traffic levels cannot be substituted.

11. 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

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 forRigid Pavement • Four subgrade strengths:

15. Subgrade Categories forFlexible 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. 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

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. 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

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. PCN Batch Mode

27. Additional Computational Modes

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. Flexible Pavements

30. Rigid Pavements

31. Processing COMFAA Output

32. Processing COMFAA Output

33. Form 5010 Elements

34. Interpretation of Results

35. Interpretation of Results

36. 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?

37. 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?

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