1. Presented to: 2010 FAA Worldwide Airport Technology Transfer Conference By: Gordon Hayhoe, FAA AJP-6312, WJHTC Date: April 20, 2010 Federal Aviation Administration PCN and CDF Overload Methods

2. 2 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 20082 ICAO ACN Overload Criteria Chapter 2 of the ICAO Pavement Design Manual Guidance on Overload Operations For those operations in which magnitude of overload and/or the frequency of use do not justify a detailed analysis the following criteria are suggested: a.For flexible pavements occasional movements by aircraft with ACN not exceeding 10 per cent above the reported PCN should not adversely affect the pavement. b.For rigid pavements, in which a rigid pavement layer provides a primary element of the structure, occasional movements by aircraft with ACN not exceeding 5 per cent above the reported PCN should not adversely affect the pavement. c.If the pavement structure is unknown the 5 per cent limitation should apply; and d.The annual number of overload movements should not exceed approximately 5 per cent of the total annual aircraft movements.

3. 3 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 20083 Relative ACN Values

4. 4 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 20084 Relative ACN Values

5. 5 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 20085 Exact and Approximate Rigid ACN Figure 1-4 from ICAO Pavement Design Manual, k units are MN/m 3

6. 6 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 20086  ACN Computation Pavement thickness for the overload aircraft is not the same as for the design aircraft (used to compute pavement PCN). ACN Traffic for the overload aircraft is the same as for the design aircraft (10,000 coverages). But by definition the traffic for the overload aircraft is much less than for the design aircraft.

7. 7 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 20087 Using Cumulative Damage Factor (CDF) for Overload

8. 8 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 20088 Computational Procedure 1. Compute CDF for current airplane mix 2. Check structural condition for current mix, 3. Compute CDF for overload aircraft 4. Compare CDF with and without overload aircraft 5. Evaluate increase in theoretical damage (  CDF) from overload operations

9. 9 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 20089 How to Determine  CDF Limiting Criteria? ACN R is the ratio of ACNs for the overload aircraft to the design aircraft. S t is the sensitivity of change in pavement life to change in pavement thickness. See the paper for details

10. 10 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 200810 Numerical Example - 1 Run COMFAA in Flexible ACN Mode. 737-500 at 134,000 lbs, B subgrade, ACN = 37.4 (t 1 = 27.84). Adjust load until ACN = 1.1 x 37.4 (  ACN = 0.1). 737-500 at 144,500 lbs, ACN = 41.1, (t 2 = 29.19). Represents an overload aircraft at the  ACN limit.

11. 11 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 200811 Numerical Example - 2 Run FAARFIELD with: –4-in P-401 –8-in P-109 –Balance P-154 –737-500 at 134,000 lbs and 1,200 annual departures Run Design on the subbase: –10.9-in P-154 –CDF = 1.0

12. 12 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 200812 Numerical Example - 3 Increase the load to 144,500 lbs at the same traffic and run Life –CDF = 2.14 over 20 years –Total departures to CDF of 1.0 = 11,208 in 9.3 years  CDF corresponding to  ACN = 0.1 is  CDF = 1.14 Increasing annual departures by 1,368 also gives  CDF = 1.14

13. 13 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 200813 Numerical Example - 4 Therefore a  CDF can represent either an increase in load or an increase in traffic, or a combination of the two. But a  ACN is affected only by an increase in load. Traffic is fixed and the structure is a dependent variable.

14. 14 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 200814 Numerical Example - 5 Add a true overload aircraft to the 737-500 at 134,000 lbs. –787 at 486,000 lbs at 12 annual departures Run Life: –CDF = 1.05 –  CDF = 0.05 –CDF for the 737 = 1.0 –CDF for the 787 = 0.65

15. 15 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 200815 Numerical Example - 6

16. 16 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 200816 Numerical Example - 7

17. 17 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 200817 Numerical Example - 8 737 ACN = 37.4. 787 ACN = 80.1, does not meet the  ACN criterion. Probably need to apply a minimum total number of departures for overload aircraft with CDF >= 1.0, at least 240, maybe as many as 1,000. Also remember tire pressure.

18. 18 Federal Aviation Administration Overload for FAA TT Conference April 20, 2010 February 20, 200818 ACN-PCN versus CDF Is it possible to compare the ACN- PCN procedure with the CDF procedure and to derive compatible overload criteria? Is the equation derived in the paper valid?