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ACN-PCN – Technical Evaluation
Example: Flexible Pavement
PCN Calculation
35
Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
35
ACN-PCN – Technical Evaluation
Basic Steps to Determine Pavement Classification Number
1) Identify pavement features and properties
2) Determine traffic mixture
3) Convert traffic to equivalent traffic of “critical” airplane
4) Determine allowable operating weight of critical airplane
5) Determine ACN of critical airplane at allowable weight
6) Report PCN
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Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
36
ACN-PCN – Technical Evaluation
1) Identify pavement features and properties
The pavement must be referenced to a standard pavement
section for evaluation purposes
5” 19 “ P-154
P-401
Asphalt
P-154 Subbase Course
P-209 Base Course
Minimum required asphalt surface layer
Minimum required P-209 layer (CBR +80)
Variable P-154 layer (CBR +20)
Minimum requirements defined in AC 150/5320-6D
37
Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
37
ACN-PCN – Technical Evaluation
For this example assume the following existing pavement
structure (must express in terms of minimum layer requirements)
5” P-401
8” P-209
19 “ P-154
SUBGRADE CBR = 9.0
10” P-401
12” P-209
21.5” P-209
4” P-401
18.25” P-401 19 “ P-154
10” P-401
All sections are structurally equivalent to 32 inch pavement
Section
defined in
terms of
minimum
layer
requirements
38
Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
38
ACN-PCN – Technical Evaluation
2) Determine Traffic Mixture
Identify the airplanes that have or plan to use the airport
during the pavement design period
Include all significant traffic
Non-scheduled events
Charters
Etc.
39
Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
39
ACN-PCN – Technical Evaluation
For this example assume the following traffic mixture
Airplane
Operating Weight,
(lbs)
Tire
Pressure
(psi)
Annual
Departures
B727-200 185,000 148 400
B737-300 130,000 195 6,000
A319-100 145,000 196 1,200
B747-400 820,000 200 3,000
B767-300ER 370,000 190 2,000
DC8-63 330,000 194 800
A300-B4 370,000 217 1,500
B777-200 600,000 215 300
40
Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
40
ACN-PCN – Technical Evaluation
3) Convert traffic to equivalent traffic of critical airplane
a) Determine traffic volume in terms of traffic cycles
b) Determine the pavement thickness necessary for each
individual airplane
The airplane requiring the thickest pavement becomes the critical
airplane
c) Traffic conversion performed in two stages
Equivalent departures based on gear type
Ratio of wheel loads
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Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
41
ACN-PCN - Coverages
Pavement design calculations require knowing how many
times the pavement is fully loaded. One full load application
is called a “Coverage”.
However, airplane operations are easily counted by how
many times the airplane “passes” over a pavement
Because airplanes seldom travel along the exact same line
of pavement, It may take many passes to fully load a unique
point in the pavement
The ratio of Passes to Coverages (P/C) is used to convert
counted passes to coverages. The ratio is unique for each
airplane.
42
Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
42
ACN-PCN - Coverages
FAA pavement design procedures use “Annual Departures”
as the traffic count for design purposes.
- Arrival traffic is ignored
-- One landing and takeoff = one Annual Departure
This may not be the best representation of the airport traffic
depending upon airport operations
43
Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
43
ACN-PCN - Coverages
Assumed procedure for FAA pavement design
Airplane is refueled – arrival weight < departure weight
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