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Equivalent Traffic
Cycle conversion
R1= Equivalent Traffic cycles of
critical airplane
R2= Traffic cycles of given
airplane expressed in terms of
critical gear
W1=Wheel load of critical airplane
W2=Wheel load of airplane in
question
W
Log R Log R W
1
2
1 2 = × Airplane
(W2)
Single
Wheel
Load, lb
(R2)
(2D) TC
(A)1/2
Wheel
Load
Ratio
(R1)
Equivalent
747-400 TC
727-200 43,938 256 0.950 194
737-300 30,875 3,840 0.796 716
A319-100 34,438 768 0.841 268
747-400 48,688 3,000 1.000 3000
767-200ER 43,938 2,000 0.950 1,368
DC8-63 39,188 800 0.897 403
A300-B4 43,938 1,500 0.950 1,041
777-200 47,500 468 0.988 434
12,632 7,424
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Spreadsheet for calculation of equivalent traffic
ACN-PCN – Technical Evaluation
69
Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
69
Spreadsheet for calculation of equivalent traffic
ACN-PCN – Technical Evaluation
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ACN-PCN – Technical Evaluation
4) Determine allowable operating weight of critical airplane
Using COMFAA
• In pavement thickness mode,
• Enter the critical airplane at the equivalent departure level
• Iterate to the known pavement thickness by changing the
airplane weight
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ACN-PCN – Technical Evaluation
Determine the maximum gross weight permitted on the
known pavement section for the “critical” airplane.
Critical airplane 747-400
Known pavement thickness 32.0 inches
Subgrade CBR 9.0 (Code B)
Tire pressure 200 psi (Code X)
Percent Weight on the main gear 95.0 %
P/C ratio 1.73
Pavement life 20 years
Annual equivalent departures (TC) 7,424
Total Coverages (TC/1.73) x 20 85,827
ACN-PCN – Technical Evaluation
Iterate to find allowable
weigh which produces
the know pavement
thickness
Enter total coverage or
departure level and
CBR
In pavement
thickness mode
ACN-PCN – Technical Evaluation
4) Determine ACN of critical airplane at allowable weight
Using COMFAA
• In ACN Computation mode,
• Enter the critical airplane at the allowable operation weight
Note that coverages defaults to 10,000 per ICAO procedure
• Calculate ACN
coverage will default to
10,000
Read ACN for desired
subgrade category
ACN-PCN – Technical Evaluation
Enter allowable
operating weight
In ACN
Computation mode
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ACN-PCN – Technical Evaluation
Using the previous parameters, the B747 could operate at
797,500 lbs
From COMFAA, determine ACN values at this weight.
= 56/F/B/X/T
This evaluation would suggest minor restriction of 2 airplanes
with ACN’s over the PCN value
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ACN-PCN – Using Technical Method
Using Technical Method of PCN (flexible example)
PCN = 56/F/B/X/U
Airplane
Operating
Weight, lbs
Tire Pressure
(psi)
% GW
Main Gear
For ACN
AC
N
F/B
Annual
Departures
B727-200 185,000 148 96.00 48 400
B737-300 130,000 195 90.86 32 6,000
A319-100 145,000 196 92.60 34 1,200
B747-400 820,000 200 93.32 59 3,000
B767-300ER 370,000 190 92.40 50 2,000
DC8-63 330,000 194 96.12 53 800
A300-B4 370,000 205 94.00 57 1,500
B777-200 600,000 215 95.42 52 300
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Case Study
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ACN-PCN – Case Study
Consider the following pavement section
Category B subgrade support
P-501 Concrete
Effective Support
Existing thickness = 18.25 inches
Flexural Strength = 700 psi,
Effective K-value = 323 pci
Sections comprised of P-304 and P-155
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