presented to: 2010 faa worldwide airport technology transfer conference by: gordon hayhoe, faa...
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Presented to: 2010 FAA Worldwide Airport Technology Transfer Conference
By: Gordon Hayhoe, FAA AJP-6312, WJHTC
Date: April 20, 2010
Federal AviationAdministration
PCN and CDF Overload Methods
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ICAO ACN Overload CriteriaChapter 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.
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Relative ACN Values
2
1
2
1
2
Pavements FlexibleFor
tt
ACNACN
2
1
2
1
2
Pavements RigidFor
tt
ACNACN
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Relative ACN Values
2aircraft of ACN1aircraft of ACN
2
1
ACNACN
coverages 10,000at 2aircraft for cknessDesign thicoverages 10,000at 1aircraft for cknessDesign thi
2
1
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Exact and Approximate Rigid ACN
0
10
20
30
40
50
60
70
80
0 100 200 300 400 500 600
Reference Slab Thickness, h, mm
Der
ived
Sin
gle
Whe
el L
oad,
DSW
L, to
nnes
k = 150 80 2040
Dark lines areDSWL = Constant * h2
2Constant1000
2 tDSWLACN
Figure 1-4 from ICAO Pavement Design Manual, k units are MN/m3
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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.
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Using Cumulative Damage Factor (CDF) for Overload
IIT
IF
II
CDFCDF
NNCDF
Rule) sMiner'(by
NI = number of coverages applied to a pavement by aircraft I NIF = number of coverages to failure for aircraft I
CDFT = Total CDF for all aircraft in the traffic mix
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Computational Procedure
1. Compute CDF for current airplane mix2. Check structural condition for current mix, 3. Compute CDF for overload aircraft4. Compare CDF with and without overload
aircraft5. Evaluate increase in theoretical damage
(CDF) from overload operations
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How to Determine CDF Limiting Criteria?
• ACNR is the ratio of ACNs for the overload aircraft to the design aircraft.
• St is the sensitivity of change in pavement life to change in pavement thickness.
• See the paper for details
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Numerical Example - 1• Run COMFAA in Flexible ACN Mode.
• 737-500 at 134,000 lbs, B subgrade, ACN = 37.4 (t1 = 27.84).
• Adjust load until ACN = 1.1 x 37.4 (ACN = 0.1).
• 737-500 at 144,500 lbs, ACN = 41.1, (t2 = 29.19). Represents an overload aircraft at the ACN limit.
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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
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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
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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.
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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
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Numerical Example - 6
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Numerical Example - 7
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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.
787 Annual Deps.
Total CDF
737 CDF
787 CDF
12 1.05 1.00 0.65 24 1.35 1.00 1.31 36 2.00 1.00 1.96 48 2.65 1.00 2.62
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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?
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