COMFAA 3.0 Beta

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COMFAA 3.0 Beta
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Acknowledgments

• Gordon Hayhoe, Rodney Joel and Jeff Rapol, FAA.
• Ken DeBord and Mike Roginski, Boeing Commercial
  Airplane Co.

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Outline

• Brief review of ACN/PCN system and ICAO
  definitions.
• FAA guidance on PCN calculation.
• Draft AC 150/5335-5B and computer programs
  (COMFAA 3.0 and new support program).
• Flexible example using COMFAA 3.0.
• Rigid example using COMFAA 3.0 for a large hub
  airport.
• Using COMFAA 3.0 additional features.

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The ACN/PCN System - General

• Aircraft Classification Number (ACN) is specified
  as a standard by ICAO in Annex 14 to the
  Convention on International Civil Aviation.
• Aircraft manufacturers are required to publish
  properly computed ACN values for all of their
  aircraft.
• Pavement Classification Number (PCN) procedures
  are given in the ICAO Aerodrome Design Manual,
  Part 3, Pavements.
• The PCN procedures in the manual are for guidance
  only and a great deal of latitude is provided.
• Airport operators are responsible for determining
  and publishing PCN values for runways.

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ICAO Documents
Annex 14 to the Convention on International Civil
Aviation
ICAO Aerodrome Design ManualPart 3 Pavements
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ACN/PCN System - Definitions

• ACN A number expressing the relative effect of
  an aircraft on a pavement for a specified
  standard subgrade strength.
• PCN - A number expressing the bearing strength of
  a pavement for unrestricted operations.
• Therefore, if a particular aircraft at a given
  weight has an ACN less than, or equal to, the PCN
  of a particular pavement (ACN ? PCN), then no
  restrictions need to be placed on operation of
  that aircraft on that pavement.
• Special provisions for overload evaluation.

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ACN Computation

• ACN is computed as the ratio of a computed
  (derived) single-wheel load to a reference
  single-wheel load.
• Flexible Based on the US Army Corps of Engineers
  ESWL CBR method of design using alpha factors
  adopted by ICAO October 2007. Thickness is
  computed for 10,000 coverages.
• Rigid PCA Westergaard interior stress method of
  design. Thickness is computed for 10,000
  coverages.
• These are fixed, standard procedures. Other
  design procedures or traffic levels cannot be
  substituted.

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Subgrade Strength for ACN Computation

• Flexible The CBR of the subgrade soil.
• Rigid The k-value at the top of the support,
  including all subbase layers.
• It is not the same as the k-value of the subgrade
  soil.

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PCN Reporting Format

• 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 in this example)
• Pavement Type (F Flexible, R Rigid)
• Subgrade Strength Category (A, B, C or D)
• Allowable Tire Pressure (X ? 1.5 MPa 218 psi)
• PCN Evaluation Method (U Using, T Technical)

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Proposed Change to ICAO PCN Tire Pressure Limits
(Flexible Only)
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PCN Using Aircraft Method

• Find the ACN of all of the aircraft regularly
  using the pavement and pick the largest ACN to be
  the PCN of the pavement.
• But see page 3-27 of the 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.
• Where is the line between regular and overload
  operation?

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PCN Technical 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.

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FAA Guidance on PCN Calculation

• The FAA is responsible for certifying all
  commercial airports in the U.S. and is the
  organization generally responsible for complying
  with international agreements on aviation.
• Well defined procedures are therefore required
  for determining and publishing PCN values for
  runways at all commercial airports in the U.S.

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AC 150/5335-5A (2006)Standardized Method of
Reporting Airport Pavement Strength PCN

• Complete rewrite of AC 150/5335-5.
• Standardized the procedures for computing and
  reporting PCN values for inclusion in the 5010
  database.
• AC 150/5335-5A is based in large part on the
  procedures described in Boeing Report D6-82203
  Precise Methods for Estimating Pavement
  Classification Number, 1998.
• D6-82203 is, in turn, based largely on
  recommendations contained in the ICAO Aerodrome
  Design Manual.

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Draft Advisory Circular 150/5335-5B

• AC 150/5335-5A, PCN, to be replaced by AC
  150/5335-5B.
• Draft AC was posted for comment October 2009.
• Comment period has ended.
• Copy of draft AC is included on the CD.

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AC 150/5335-5B STANDARDIZED METHOD OF REPORTING
AIRPORT PAVEMENT STRENGTH - PCN

• The Pavement Classification Number (PCN) field
  has been added to FAA Form 5010 and data
  collection is underway.
• During each airport inspection, the airport owner
  will be asked to provide runway PCN information.
• WHY?
• With release of AC 150/5320-6E, the design
  aircraft concept has been replaced.
• This means the Aircraft Gross Weight fields on
  the 5010 will no longer be used to describe load
  carrying capacity of runways.

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AC 150/5335-5B PCN
Gross Weight data may transition.
PCN data request now part of all airport
inspections

• The Master Record is required to be updated
  periodically.
• PCN is now mandatory and Gross Weight data will
  possibly be phased out with time.

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Draft AC 150/5335-5B - Changes from AC
150/5335-5A

• The procedure for selecting the critical aircraft
  has been substantially revised.
• The procedure for computing equivalent departures
  has been replaced by a new procedure based on
  cumulative damage factor (CDF).
• Except for obtaining the structure and aircraft
  properties, the procedure has been completely
  automated in a revised version of the computer
  program COMFAA (COMFAA 3.0).
• A spreadsheet application has been developed to
  facilitate determining the evaluation thickness.

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Draft AC 150/5335-5B

• The design procedures recommended in the new AC
  are
• CBR ESWL with the new alpha factors for flexible
  pavements.
• Edge stress Westergaard as implemented in AC
  150/5320-6C and -6D.
• The PCA center stress method can also be selected
  in COMFAA 3.0.
• These were selected for backward compatibility
  with established methods and compatibility with
  the ACN computation procedure.

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New PCN Methodology

• The current methodology (-5A) finds the critical
  aircraft and then finds the ACN of that aircraft
  at the maximum allowable gross weight. That ACN
  is then the PCN.
• The new methodology is the same except that the
  ACN at maximum allowable gross weight is
  calculated for all of the aircraft in the mix.
  The CDF procedure is used for equivalent
  coverages.
• The largest ACN value is then selected as the
  PCN.
• There is a need to eliminate occasional or
  overload aircraft from the mix.

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ACN-PCN Technical Evaluation

• 7 Basic Steps to Determine Pavement
  Classification Number in AC 150/5335-6B
• Identify pavement features and properties.
• Determine traffic mixture.
• Convert traffic to equivalent traffic of
  critical aircraft.
• Determine allowable operating weight of critical
  airplane.
• Determine ACN of critical airplane at allowable
  weight.
• Repeat with each airplane the critical airplane.
• Report PCN.

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AC 150/5335-5B Computer Programs

• COMFAA 3.0 Program
• Support Spreadsheet for COMFAA (Excel)
• Input Support
• Flexible Layer Equivalency Worksheet
• Rigid Pavement k-Value Worksheet
• Output Support
• Output Data Parsing
• Rigid and Flexible Chart Creation
• FAA Form 5010 Preparation

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COMFAA Support Spreadsheet

• Flexible Layer Equivalency
• The equivalent pavement has three layers
• 5 in. P-401,
• 8 in. P-209,
• P-154.
• The spreadsheet determines the maximum thickness
  for the equivalent pavement based on the
  user-defined layer equivalency factors.

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COMFAA Support SpreadsheetFlexible Pavement Input

• ENTER (or confirm) layer equivalency factors.
• Refer to Table A2-1.
• ENTER all existing pavement layers starting at
  the surface of the pavement.
• ENTER the subgrade CBR value.

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COMFAA Support SpreadsheetFlexible Pavement
Output

• The spreadsheet determines and consolidates
  COMFAA software input values and recommends three
  of five necessary PCN codes.
• The spreadsheet updates the graphical
  representation of the existing and equivalent
  pavement.

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Using the COMFAA 3.0 Program
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COMFAA Input
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Aircraft Window COMFAA Input
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Main Window - COMFAA Input
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COMFAA Output
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COMFAA Detailed Output Screen
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COMFAA Output Details (I)

• PCN based on using aircraft ACN can be reported
  as 54.

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COMFAA Output Details (II)
COMFAA generates a table based on the CDF method.
For each aircraft, allowable gross weight and
corresponding PCN are identified.
CBR 9 indicates B subgrade designation.
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COMFAA Output Details (III)

• CDF method identifies (3) aircraft that
  contribute substantial structural damage based on
  pavement structure 727-200, 747-400, and
  A300-B4.
• PCN based on technical CDF method can be reported
  as the highest PCN of these aircraft 73.

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COMFAA Detailed Output Screen
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COMFAA Support Spreadsheet

• Data Parse
• Copy/Paste output data into Cell B5
• Click Create Flexible Pavement Charts
• Airplanes are ordered by PCN number, with the
  aircraft at top giving the highest PCN when
  treated as critical.

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COMFAA Support SpreadsheetFlexible Charts

• Thickness Comparison
• Compare thickness and gross weights.
• When CDF thickness (yellow) is less than
  evaluation thickness (red), excess PCN is
  available.

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COMFAA Support SpreadsheetFlexible Charts

• PCN Comparison
• PCN needed for using traffic is 54.
• PCN based on CDF analysis can be reported as high
  as 73.

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Technical Method Example Case 1

• International hub airport.
• Rigid pavement.
• Large number of narrow-body, dual-wheel-gear
  aircraft.
• Example courtesy of Rodney Joel.

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CASE 1

• Traffic Data

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CASE 1

• Existing Pavement Data

Effective k at top of base 323 psi/in
17? PCC, R 775 psi
8? CTB
k-value 160 psi/in
The original design based on procedures in AC
150/5320-6D called for 16.3 inches of PCC. This
value was rounded to 17.0 inches.
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CASE 1

• Pavement thickness requirements based on actual
  annual departures
• FAA AC 150/5320-6D
• PCA method
• B737-700 appears to be the design airplane
  based on 5335-5A procedures.
• B737-700 is comprised of several D gear airplanes.

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CASE 1 Current Procedure

• Following 5335-5A procedures the B737-700 would
  become the Critical Aircraft due to its
  individual pavement thickness requirement.
• This is true for either the 5320-6D procedure or
  the PCA center slab procedure.
• It was speculated that the B737 was artificially
  elevated as the design airplane due to high
  departure levels caused by lumping several D-gear
  airplanes into one.

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CASE 1

• PCN values calculated by following the procedures
  in AC 150/5335-5A and assuming that each airplane
  is the design airplane.
• In this mix, the B737-700 is comprised of several
  D gear airplanes, some with lower operating
  weights.

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CASE 1
Airplanes can operate without restriction

• ACN values for each airplane (from COMFAA)
• Assuming the B737-700 as the design airplane per
  the procedures in 5335-5A
• Calculated PCN 59.8/R/BPCN (60/R/B)

Weight Restrictions
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Case 1 New CDF PCN Procedure

• The procedure for finding equivalent coverages in
  AC 150/5335-5A is based on gear equivalency
  factors and the ratio of wheel loads.
• An alternative procedure based on cumulative
  damage factors (CDF) gave more consistent, and
  rational, results.
• The new procedure for finding equivalent
  coverages has been incorporated in the new AC
  150/5335-5B.

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COMFAA 3.0 Case 1
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COMFAA Support Spreadsheet

• Rigid Pavement k-Value
• Each subbase layer contributes to an improved
  subgrade support k-value.
• ENTER all existing pavement layers.
• ENTER the flexural strength of the concrete and
  the subgrade support k-value.
• The spreadsheet updates the graphical
  representation of the existing and equivalent
  pavement.

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COMFAA 3.0 Aircraft Window
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COMFAA 3.0 Case 1 Results
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COMFAA 3.0 Case 1 Results
Copy and Paste Data into Support Spreadsheet
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COMFAA Support SpreadsheetCase 1

• Data Parse
• Copy/Paste output data into Cell B5
• Click Create Rigid Pavement Charts
• Airplanes are ordered by PCN number, with the
  aircraft at top giving the highest PCN when
  treated as critical.
• Next, click Rigid Chart tab.

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COMFAA Support SpreadsheetRigid Charts Case 1

• Thickness Comparison
• Compare thickness and gross weights.
• When CDF thickness (yellow) is less than
  evaluation thickness (red), excess PCN is
  available.

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COMFAA Support SpreadsheetRigid Charts Case 1

• PCN Comparison
• 6 most demanding aircraft in mix.
• PCN needed for using traffic is 70.
• PCN based on CDF analysis can be reported as high
  as 96.
• Next, click on Form 5010 tab.

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COMFAA Support SpreadsheetRigid Charts Case 1

• Form 5010
• Enter PCN Number.
• PCN can be reported as96/R/B/W/T

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Case 1 PCN ComparisonPCN calculated assuming
each airplane is treated as the design airplane
A380
B747
B777
B757
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COMFAA 3.0 Options

• Batch
• Runs all airplanes in succession.
• Automatically invoked by PCN Flex and Rigid Batch
  function.
• Metric
• PCA Thick
• Equivalent coverages computed with the PCA
  interior stress design method.
• PCA GW
• Maximum gross weight computed with the PCA
  interior stress design method.

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COMFAA 3.0 Computational Modes

• ACN Computes ACN at indicated gross weight
  strength.
• PCN Computes PCN using CDF-based procedure.
• Thickness Computes by AC 150/5320-6D procedure.
• MGW Computes maximum gross weight for airplane.
• Life Computes coverages to failure for
  indicated thickness.
• Interior Stress
• Edge Stress

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COMFAA 2.0 Will Continue to be Supported
Simpler and Old Alphas
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More Information

• Contact Dr. Gordon Hayhoe
• Gordon.Hayhoe_at_faa.gov
• FAA Airport Technology RD Group
• www.airporttech.tc.faa.gov
• Click on Downloads then Pavements

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Questions?