**Development of a Computer Program  COMFAA  for Calculating Pavement
Thickness and Strength**

**June 4, 2003**

**Federal Aviation Administration**

**Airport Technology Research and Development Branch**

**William J. Hughes Technical Center**

**Atlantic City International Airport**

**New Jersey, 08405**

TABLE OF CONTENTS

[Section]{.underline} [Page]{.underline}

[1. INTRODUCTION 1](#introduction)

[1.1 ACN Computation Mode 1](#acn-computation-mode)

[1.2 Design Pavement Mode 1](#design-pavement-mode)

[2. PROGRAM MODIFICATIONS 1](#program-modifications)

[2.1 Additions to the Aircraft Library
3](#additions-to-the-aircraft-library)

[2.2 Metrication of COMFAA 3](#metrication-of-comfaa)

[2.3 Installation of the PCC Design Model from AC 150/5320-6D
4](#installation-of-the-pcc-design-model-from-ac-1505320-6d)

[2.3.1 Installation of Visual Basic Version of H51
4](#installation-of-visual-basic-version-of-h51)

[2.3.2 Extension of H51 Capabilities 5](#extension-of-h51-capabilities)

[2.4 Calculation of Slab Thickness 6](#calculation-of-slab-thickness)

[2.5 Reliability of COMFAA 10](#reliability-of-comfaa)

[2.5.1 ACNS Calculated Using the COMFAA, ACNR, and ACNF Programs
10](#acns-calculated-using-the-comfaa-acnr-and-acnf-programs)

[2.5.2 ACN Numbers for C-17A on Rigid Pavements
12](#acn-numbers-for-c-17a-on-rigid-pavements)

[2.5.3 Slab Thickness Calculated Using COMFAA and AC 150/5320-6D
14](#slab-thickness-calculated-using-comfaa-and-ac-1505320-6d)

[2.6 Analysis of Two Closely Spaced Triple Twin Tandems Using COMFAA
15](#analysis-of-two-closely-spaced-triple-twin-tandems-using-comfaa)

[3. REFERENCES 18](#references)

[APPENDIXES]{.underline}

[A Characteristics of Aircraft Added to
COMFAA](#__RefHeading___Toc9328113)

[B Comparison of Results Calculated by H51 FORTRAN and Visual Basic
Versions](#__RefHeading___Toc9328114)

[C Rigid and Flexible Pavement ACNs for Aircraft Added to
COMFAA](#__RefHeading___Toc9328115)

[D Wheel Arrangement for Complex Gear
Configurations](#__RefHeading___Toc9328116)

LIST OF ILLUSTRATIONS

[Figure]{.underline} [Page]{.underline}

[Figure 1. Graphical User Interface for COMFAA Displaying Data in Metric
Units 4](#__RefHeading___Toc12261916)

[Figure 2. Calculation of Slab Edge Stress for Any Wheel Location Using
the Concept of Superposition 5](#__RefHeading___Toc12261917)

[Figure 3. Search Paths for Maximum Stress Location
6](#__RefHeading___Toc12261918)

[Figure 4. Algorithm for Calculating Slab Thickness
8](#__RefHeading___Toc12261919)

[Figure 5. COMFAA Graphic Interface with Design Thickness Result
9](#__RefHeading___Toc12261920)

[Figure 6. COMFAA Results for C-17A Aircraft
13](#__RefHeading___Toc12261921)

[Figure 7. COMFAA Results for Three Wheels out of Six on C-17A Aircraft
14](#__RefHeading___Toc12261922)

[Figure 8. Two Closely Spaced Triple Twin Tandems
16](#__RefHeading___Toc12261923)

[Figure 9. Contribution of Individual Wheels to Slab Edge Stress at
Location \"A\" for Two Triple Twin Tandems (Slab Thickness = 14.90
inches (37.85 cm), k = 100 pci (27.1 kg/cm^3^))
16](#__RefHeading___Toc12261924)

[Figure 10. Contribution of Individual Wheels to Slab Edge Stress at
Location \"A\" for Two Triple Twin Tandems (Slab Thickness = 12.62
inches, k = 200 pci) 17](#__RefHeading___Toc12261925)

[Figure 11. 3-D Surface of Edge Stress Depending on Wheel Position at
Coordinates x and y (Slab Thickness = 12.62 inches, k = 200 pci)
17](#__RefHeading___Toc12261926)

[Figure 12. Surface Chart, Viewed from Above, of Edge Stress Depending
on Wheel Position at Coordinates x and y (Slab Thickness = 12.62 inches,
k = 200 pci) 18](#__RefHeading___Toc12261927)

LIST OF TABLES

[Table]{.underline} [Page]{.underline}

[1. Aircraft Added to COMFAA Library 3](#__RefHeading___Toc9328141)

[2. ACNs for IL75T Aircraft 11](#__RefHeading___Toc9328142)

[3. ACNs for IL75T Aircraft 11](#__RefHeading___Toc9328143)

[4. ACNs for Selected Aircraft on Rigid Pavements
12](#__RefHeading___Toc9328144)

[5. ACNs for Selected Aircraft on Flexible Pavements
12](#__RefHeading___Toc9328145)

[6. ACNs for C-17A Aircraft on Rigid Pavements
13](#__RefHeading___Toc9328146)

[7. ACNs for Three out of Six Wheels for C-17A Aircraft on Rigid
Pavements 13](#__RefHeading___Toc9328147)

[8. Input Data for Thickness Designs 14](#__RefHeading___Toc9328148)

[9. Results of Thickness Designs 15](#__RefHeading___Toc9328149)

[10. Comparison of Design Thicknesses Obtained by AC 150/5320-6C and
COMFAA 15](#__RefHeading___Toc9328150)

ACRONYMS AND ABBREVIATIONS

AC Advisory Circular

ACN Aircraft Classification Number

ACNF ICAO Program for Calculating ACNs for Flexible Pavements

ACNR ICAO Program for Calculating ACNs for Rigid Pavements

CBR California Bearing Ratio

cm Centimeter

FAA Federal Aviation Administration

GW Gross Weight of the Aircraft

HTML Hyper Text Markup Language

ICAO International Civil Aviation Organization

k Modulus of Subgrade Reaction

kg Kilogram

kp Kilopound

LEDFAA Layered Elastic Design - FAA

MN/m^3^ Meganewton per Cubic Meter

Mpa Megapascal

PCA Portland Cement Association

PCC Portland Cement Concrete

pci Pounds per Cubic Inch

psi Pounds per Square Inch

Rc Concrete Flexural Strength for PCC Layer

RTBIS Function Using Bisection Method for Finding Root of the Equation

# INTRODUCTION

COMFAA is a general-purpose program that operates in two computational
modes: Aircraft Classification Number (ACN) Computation Mode and Design
Pavement Mode. This program is based on modifications made to the FAA's
ACNComp computer program dated August 1997.

## ACN Computation Mode

In ACN Computation Mode, COMFAA performs the following functions:

a.  Calculates the ACN for aircraft on flexible pavements.

b.  Calculates the ACN number for aircraft on rigid pavements.

c.  Calculates flexible pavement thickness based on the California
    Bearing Ratio (CBR) method in Advisory Circular (AC) 150/5320-6D for
    default values of CBR (15, 10, 6, and 3).

d.  Calculates rigid pavement slab thickness based on the Portland
    Cement Association (PCA) method for default values of k (552.6,
    294.7, 147.4, and 73.7 lb/in^3^ -- 150.0, 80.0, 40.0, and 20.0
    kg/cm^3^).

## Design Pavement Mode

In Design Pavement Mode, COMFAA:

a.  Calculates flexible pavement thickness based on the CBR method in AC
    150/5320-6D for the CBR value specified by the user.

b.  Calculates rigid pavement slab thickness based on Federal Aviation
    Administration (FAA) AC 150/5320-6D for the k value specified by the
    user.

ACNs are calculated according to Annex 14 of the International Civil
Aviation Organization (ICAO) Airport Pavement Design Manual. The
computer programs listed in Appendix 4 of the ICAO manual have been
implemented in COMFAA and these implementations are believed to
accurately reproduce the ACNs computed by the ICAO programs. However,
inconsistencies may exist between the ICAO listings and the COMFAA
implementations. COMFAA is not a substitute for the ICAO programs.

# PROGRAM MODIFICATIONS

The following modifications were made to ACNComp, August 1997 version,
to develop the COMFAA program:

a.  ACNCOMP was checked and modified so that the characteristics for the
    aircraft in the internal library and listed in the current edition
    of the ICAO publication, \"Aerodrome Design Manual: Part 3 --
    Pavements\" \[a.\], are in agreement.

b.  Thirty aircraft were added to the aircraft library. COMFAA now
    contains all of the aircraft in the current edition of the ICAO
    Design Manual \[a.\].

c.  The frame labeled \"Computational Mode\", with two option buttons,
    was added to the Graphic User Interface. The user now has the option
    to select either the ACN Computation mode or the Pavement Design
    mode.

d.  The Portland Cement Concrete (PCC) design model from FAA AC
    150/5320-6D \[b.\] was installed. The thickness design in this
    version is now based on edge stress, rather than interior stress.

e.  The user cannot change the aircraft tire pressure in the ACN
    Computation Mode or the Tire Contact Area in the Pavement Design
    Mode unless the aircraft is in the external library.

f.  When the user saves an aircraft in the external library, an
    additional parameter, Tire Contact Area, is saved in the external
    file, ACNacrft.Ext.

g.  H51 \[c.\] capabilities were extended to include slab stress
    calculations for gear configurations not included in the H51
    program.

h.  Metrication was added.

i.  The Conventional Windows Help File was updated and converted into an
    HTML help file format. The updates to the Help File text include the
    following:

    1.  An explanation that the slab thickness is calculated from
        interior stress if the user does not specify a k value and from
        edge stress if the user specifies a k value when using the
        \"Change Pavement Structure\" feature.

    2.  Information was added regarding the Rc (concrete flexural
        strength for PCC layer) field in the output grid for the topic
        \"Change Pavement Structure.\"

j.  The readme.txt file was modified.

k.  It was discovered that a cutoff value larger than the 3\* (Radius of
    Relative Stiffness) standard by ICAO is required for the C-17A to
    avoid unreasonable results for ACNs.

l.  The reliability of the calculations affected by the modifications
    was evaluated and verified to be accurate.

m.  Dimensions for the C-17A gear configuration were modified according
    to the report \"C-17 Pavement Design and Evaluation Criteria.\"

Details of the work performed are given in the following sections.

## Additions to the Aircraft Library

A comparison of the aircraft contained in the ICAO Design Manual and
COMFAA was conducted. Table 1 lists the 30 aircraft that were added to
the existing list of 60 aircraft in the COMFAA internal library as a
result of the comparison. Appendix A contains the aircraft
characteristics.

[]{#__RefHeading___Toc9328141 .anchor}Table 1. Aircraft Added to COMFAA
Library

  ----------------------- -------------- ---------------------------------
  Aircraft Group          Number         Added Aircraft Type

  Airbus                  1              A-310-200

                          2              A-320 Dual Tandem

  Boeing                  3              B-720

  McDonnell Douglas       4              DC-3

                          5              DC-4

                          6              DC-8-43

                          7              DC-10-15

                          8              MD-87

  Other Commercial        9              BAC 1-11 Series 400

                          10             BAC 1-11 Series 475

                          11             Caravelle 10

                          12             Caravelle 12

                          13             Canadair CL-44

                          14             CV 880 M

                          15             CV 990

                          16             Dash 7

                          17             F27 Friendship Mk500

                          18             F28 Fellowship Mk1000LPT

                          19             F28 Fellowship MK1000HTP

                          20             Fokker 50 HTP

                          21             HS125

                          22             HS748

                          23             IL62

                          24             IL76T

                          25             IL86

                          26             L-100-20

                          27             Trident 1E

                          28             TU134A

                          29             TU154B

                          30             VC10-1150
  ----------------------- -------------- ---------------------------------

## Metrication of COMFAA

Metrication was added to COMFAA similar to the metrication in LEDFAA. It
does not affect the calculations conducted by COMFAA, which are in
English units, as was done before metrication was added to the program.
Metrication only affects values displayed by the graphical interface.
For example, calculations with the variable \"TirePressure\" always use
the unit, pounds per square inch (psi). The value to be displayed for
the tire pressure is the value of \"TirePressure\" (in psi) multiplied
by a conversion coefficient that is assigned dependent on the condition
of the checkbox for metric values located in the lower left corner of
the main window, as shown in figure 1. The user can enter the value of
tire pressure in either English or Metric units.

> NOTE: For \"TirePressure,\" the value of the conversion coefficient is
> 1 when tire pressure is entered in English units or 6.894757 when tire
> pressure is entered in Metric units.

![](media/image1.png){width="5.0in" height="3.75in"}

[]{#__RefHeading___Toc12261916 .anchor}Figure 1. Graphical User
Interface for COMFAA Displaying Data in Metric Units

## Installation of the PCC Design Model from AC 150/5320-6D

The following modifications were made to enable COMFAA to calculate
single-aircraft rigid pavement thickness design according to the
Westergaard-based procedure specified in FAA AC 150/5320-6D \[b.\].

### Installation of Visual Basic Version of H51

H51 \[c.\] is a FORTRAN computer program that calculates slab edge
stresses resulting from loads applied by aircraft landing gears. It is
based on the theory of a semi-infinite plate on an elastic foundation
\[c.\]. The H51 FORTRAN program was converted to Visual Basic, and the
new program (TestH51) was thoroughly debugged to ensure that the results
were the same as those from H51 within numerical roundoff. (The
comparison of the results from both programs is contained in appendix
B.) TestH51 was then installed into COMFAA and modified so that the
aircraft characteristics are read from the aircraft library. All of the
necessary input to TestH51 is provided by the COMFAA user through the
graphical interface.

### Extension of H51 Capabilities

H51 has a capability to directly calculate slab edge stresses for the
following limited number of gear configurations: single wheel, dual
(twin), dual twin, single tandem, dual (twin) tandem, dual twin tandem,
and triple dual (twin) tandem (tridem). However, H51 can be used to
calculate the slab edge stress for any gear configuration using the
concept of superposition. Figure 2 exemplifies the calculation of slab
edge stress for a wheel located at coordinates x and y using the concept
of superposition.

The calculation of the slab edge stress sA1, for a wheel located at
coordinates x and y, is accomplished in the following steps:

a.  Calculate the slab edge stress σ~A2~ for a twin tandem with
    x-transverse spacing and y-longitudinal spacing between the tires.

b.  Calculate the slab edge stress σ~A3~ for a single tandem with
    y-longitudinal spacing between the tires.

c.  Calculate the slab edge stress σ~A4~ for a single wheel displaced a
    distance x from the point of the calculated stress.

d.  Calculate the slab edge stress σ~A1~ for a wheel located at
    coordinates x and y, according to the formula σ~A1~ = σ~A2~ -
    σ~A3~ - σ~A4~.

For gear configurations not included in H51, COMFAA performs stress
calculations for all of the individual wheels of the gear. The final
slab edge stress produced by the gear is calculated from the summation
of all of the stresses produced by each wheel.

[]{#__RefHeading___Toc12261917 .anchor}Figure 2. Calculation of Slab
Edge Stress for Any Wheel Location Using the Concept of Superposition

Initially, the location of maximum stress is not known and can be
located either under one of the wheels or at some location between the
wheels. A subroutine was written based on a golden section search
procedure \[d.\], which searches for the maximum stress along the slab
edge. Two cases were analyzed, as shown in figure 3. First, when a gear
is positioned perpendicular to the slab edge, the search is conducted
along the x-axis between the points \"A\" and \"B.\" Second, when a gear
is positioned parallel to the slab edge, the search is conducted along
the y-axis between the points \"C\" and \"D.\"

![](media/image2.wmf){width="4.413888888888889in"
height="3.345138888888889in"}

[]{#__RefHeading___Toc12261918 .anchor}Figure 3. Search Paths for
Maximum Stress Location

## Calculation of Slab Thickness

The calculated maximum slab edge stress for a specified slab thickness
is compared with the maximum allowable stress for the specific PCC. If
the calculated maximum stress is significantly different from the
maximum allowable stress, the slab thickness is adjusted. For example,
the FAA program for rigid airport pavements (R805FAA) \[e.\] uses an
approximation method to estimate PCC edge stresses and obtains PCC
thickness by an iterative method. A review of the source code for
R805FAA shows that the thickness obtained is then adjusted by a
coefficient that is calculated based on the number of aircraft
coverages. A similar approach was used in a subroutine of COMFAA, the
difference being that the subroutine uses the H51 code for calculating
slab edge stresses. The purpose of this subroutine is to find the slab
thickness, H~Slab~, for which the slab edge stress, calculated by
COMFAA, satisfies the following equation:

$\sigma(H_{\text{Slab}}) \leq \frac{\text{Rc}}{1\text{.}3 \ast 0\text{.}\text{75}}$
(1)

where: σ(H~Slab~) Maximum tensile edge stress at the bottom of the slab
for slab thickness H~Slab~.

> R~c~ Flexural strength of PCC slab.
>
> 1.3 Safety factor.
>
> 0.75 Reduction factor based on the assumption that a joint may
> transfer 25 percent of the load to the other side of the joint.

The slab edge stresses are calculated for gear loads located either
parallel or perpendicular to the joint. From the two calculated
stresses, the maximum stress is selected, which satisfies equation 1.

A procedure, RTBIS, implementing a bisection method was written to find
the slab thickness H~Slab~ for which the maximum slab edge stress is
calculated by COMFAA with the precision of 0.01 inch. Figure 4 presents
a flowchart for the algorithm implemented in COMFAA.

Initially, the algorithm determines a slab thickness interval within
which the solution exists. It then starts a loop. The maximum slab edge
stress is evaluated in the middle of the interval. If the maximum stress
is higher than the maximum allowable stress, a new interval is taken
between the midpoint and the upper bound of the interval and the stress
is evaluated at the midpoint of the new interval H~Slab~ = H~Slab~ + DH
where DH is half the distance between H~Slab~ and the upper bound of the
interval. If the maximum stress is lower than the maximum allowable
stress, then the new interval is taken between the lower bound of the
interval and the midpoint and the stress is evaluated at the midpoint of
the new interval H~Slab~ = H~Slab~ -- DH, where DH is half the distance
between H~Slab~ and the lower bound of the interval. The loop continues
until the size of the interval is smaller than 0.01 inch.

Finally, the slab thickness, H~Slab~, is adjusted by a factor of *a*, as
applied in the following equation:

$H_{\text{Adj}\text{.}\text{Slab}} = \alpha \ast H_{\text{Slab}}$ (2)

where α Function for adjusting slab thickness by using the fatigue curve
developed by the Corps of Engineers from test track data and
observations of in-service pavements. Calculations are made in
accordance with the following equations \[e.\]:

$\alpha = 1 + 0\text{.}\text{15603}\text{*log}_{\text{10}}\left( \frac{\text{COVERAGE}}{\text{5000}} \right)\begin{matrix}
 & \begin{matrix}
\text{for} & (\text{COVERAGE} \geq \text{5000})
\end{matrix}
\end{matrix}$ (3)

or

$\alpha = 1 + 0\text{.}\text{07058}\text{*log}_{\text{10}}\left( \frac{\text{COVERAGE}}{\text{5000}} \right)\begin{matrix}
 & \begin{matrix}
\text{for} & (\text{COVERAGE} < \text{5000})
\end{matrix}
\end{matrix}$ (4)

Figure 5 presents a COMFAA screen with a design thickness result. COMFAA
runs calculations for rigid pavements in two different computational
modes: ACN Computation Mode and Pavement Design Mode. In the ACN
Computation Mode, ACN calculations and slab thickness calculations are
based on the slab interior stress \[a.\]. In the Pavement Design Mode,
slab thickness calculations implement the FAA Westergaard edge stress as
in the design charts in AC 150/5320-6D \[b.\].

To choose the computational mode, select the appropriate option button
in the computational mode frame, as shown in figure 5. When the option
button labeled \"ACN Computation\" is selected and the button labeled
\"ACN [R]{.underline}igid\" is clicked on, PCC slab thicknesses and ACNs
are calculated for four pavement structures having subgrades with
specified k values (552.6, 294.7, 147.4, and 73.7 lb/in^3^- 150.0, 80.0,
40.0, and 20 kg/cm^3^). These calculations are based on the slab
interior stress.

![](media/image3.wmf){width="3.779861111111111in"
height="4.882638888888889in"}

[]{#__RefHeading___Toc12261919 .anchor}Figure 4. Algorithm for
Calculating Slab Thickness

![](media/image4.png){width="4.5in" height="3.375in"}

[]{#__RefHeading___Toc12261920 .anchor}Figure 5. COMFAA Graphic
Interface with Design Thickness Result

If the option button labeled \"Pavement Design\" is selected and the
button labeled \"Rigid Design\" is clicked on, the program computes PCC
slab thickness for the k value specified by the user. (To specify the k
value, click on the field labeled \"k lb/in\^3\" and type the k value in
a message box.) These calculations are based on the slab edge stress.

For the case shown in figure 5, the design thickness of a slab is 17.90
inches (45.47 cm) on a subgrade with a k value of 100 lb/in^3^ (27.1
kg/cm^3^) and loaded with a 400,000-pound (181,437 kg) dual tandem gear
aircraft at 10,000 coverages, in which the coverages can be obtained
from the total pass number divided by the pass/coverage ratio in AC
150/5320-6D \[b.\].

## Reliability of COMFAA

The reliability of COMFAA was checked with respect to the calculation of
ACNs, slab edge stress, and slab thickness.

### ACNs Calculated Using the COMFAA, ACNR, and ACNF Programs

Appendix C, table C-1, contains a comparison of the ACNs for rigid
pavements calculated by COMFAA to those obtained from the ICAO Design
Manual \[a.\]. Appendix C, table C-2, contains a comparison of ACNs for
flexible pavements calculated by COMFAA to those obtained from the ICAO
Design Manual. From a review of tables C-1 and C-2, it can be concluded
that for 27 of the 30 added aircraft, the ACNs calculated using the
COMFAA program are similar to the ACNs obtained from the ICAO Design
Manual. Significant differences in the ACNs exist only for Canadair CL
44, DC-10-15, and IL76T aircraft. The ACNs for Canadair CL 44 calculated
by COMFAA are about 5 points higher than the ACNs obtained from the ICAO
Design Manual.

A significant difference of 5.7 points in the ACN number exists for
DC-10-15 aircraft on rigid pavements with a subgrade having k=20
MN/m^3^. Normally, the calculations of ACNs for rigid pavements are done
with the default rigid cutoff value of 3. With a rigid cutoff value of
1.23, the ACN number for a rigid pavement with a k=20 MN/m^3^ subgrade
is 72, which is closer to the ICAO Design Manual number of 74 for the
DC-10-15.

There are significant differences between ACNs calculated by COMFAA and
the ACNs obtained from the ICAO Design Manual for the IL76T aircraft.
Moreover, the ACNs for rigid pavements are unreasonable, because the ACN
number calculated by COMFAA for a rigid pavement with a subgrade having
k=20 MN/m^3^ is lower than that with a subgrade having k=40 MN/m^3^.
This is contrary to what is expected. The ACN number for aircraft
increases when the subgrade in a pavement structure becomes weaker.
However, the ICAO numbers for IL76T aircraft for rigid pavements also
appear to be unreasonable. The ACNs in this case are almost constant,
showing no effect of subgrade strength on the ACNs, contrary to the ACNs
for other aircraft.

Tables 2 and 3 show ACNs for the IL76T. Table 2 shows ACNs calculated by
COMFAA, where 23.5 percent of the load is on one main gear leg (four
main gear legs), as provided by the ICAO Design Manual. Assuming 47
percent (table 3) of the load on one main gear leg (two main gear legs),
the calculated ACN numbers are closer to the ICAO ACN numbers. However,
there are still significant differences.

[]{#__RefHeading___Toc9328142
.anchor}^Table\ 2.\ ACNs\ for\ IL76T\ Aircraft^

  ----------------------------- ----------- ------- ------- ------- ----------- ------- ------- -------
                                Rigid                               Flexible                    
                                Pavements                           Pavements                   

  ACN Calculated by the COMFAA  11.0        13.2    15.4    14.4    9.0         10.3    12.5    16.5
  Program                                                                                       

  ACN from the ICAO Design      38          38      38      39      37          40      45      53
  Manual                                                                                        

  Difference in ACN Number      -27.0       -24.8   -22.6   -24.6   -28.0       -29.7   -32.5   -36.5
  ----------------------------- ----------- ------- ------- ------- ----------- ------- ------- -------

[]{#__RefHeading___Toc9328143
.anchor}^Table\ 3.\ ACNs\ for\ IL76T\ Aircraft^

  ----------------------------- ----------- ------ ------ ------ ----------- ------- ------- ------
                                Rigid                            Flexible                    
                                Pavements                        Pavements                   

  ACN Calculated by the COMFAA  29.4        33.1   30.0   33.8   24.1        27.3    33.8    45.4
  Program                                                                                    

  ACN from the ICAO Design      38          38     38     39     37          40      45      53
  Manual                                                                                     

  Difference in ACN Number      -8.6        -4.9   -8.0   -5.2   12.9        -12.7   -11.2   -7.6
  ----------------------------- ----------- ------ ------ ------ ----------- ------- ------- ------

The minor differences between ACNs calculated by COMFAA and those
obtained from the ICAO Design Manual could be attributed to rounding of
the ACNs in the ICAO Design Manual. A comparison with programs ACNR
\[f.\] and ACNF \[g.\], which are two computer programs developed based
on \[a.\], was made to check for similar differences. The results are
presented in tables 4 and 5. For most of the gear configurations, which
can be classified as single, dual, tandem, and dual tandem, the
differences between the ACNs calculated by COMFAA and those obtained in
the ICAO design manual are very small. In most of the cases, ICAO ACNs
look like rounded numbers calculated by COMFAA. For example, for
flexible pavement (subgrade CBR=15), the COMFAA number for the A310
aircraft is 35.9, the ICAO number is 36, and the ACNF number is 35.80.
For a flexible pavement (subgrade CBR=6), the COMFAA ACN number for a
DC-10-15 is 73.4, 72 according to the ICAO Design Manual and 73.39
according to ACNF. This indicates that the ACN calculated by ACNF
supports those calculated by COMFAA. Therefore, the ACNs calculated by
COMFAA can be considered reliable and the program can be used to
calculate ACNs for the gear configurations, which can be classified as
single, dual, tandem, and dual tandem.

For the complex gear configurations, as shown in appendix D, COMFAA ACNs
are either similar to ICAO ACNs and/or to ACNF or ACNR ACNs, except for
aircraft Canadair CL 44. For Canadair CL 44 aircraft on rigid pavements,
the ICAO ACNs and ACNs calculated by ACNR are similar; however, ACNs
calculated by COMFAA are higher. Overall, COMFAA can be used to
calculate ACNs for complex configurations, since most ACNs for complex
gear configurations calculated by COMFAA are similar to either ICAO ACNs
or ACNs calculated by ACNR or ACNF.

[]{#__RefHeading___Toc9328144 .anchor}Table 4. ACNs for Selected
Aircraft on Rigid Pavements

  ----------- ------------- ------ ------ ------ ------------- ---- ---- ---- ------------- ------ ------ ------
  Aircraft    ACN by COMFAA                      ACN by ICAO                  ACN by ACNR                 
  Type                                           Design Man.                  \[f.\]                      

              Subgrade k                         Subgrade k                   Subgrade k                  
              \[MN/m^3^\]                        \[MN/m^3^\]                  \[MN/m^3^\]                 

              150           80     40     20     150           80   40   20   150           80     40     20

  A310        32.4          38.7   46.2   53.2   33            39   46   54   33            38.4   45.4   52.3

  A320 DT     16.5          19.8   23.6   27.2   18            21   24   28   16.7          19.7   23.3   26.9

  Caravelle   13.7          16.4   19.3   21.9   15            17   20   22   32.8          33.7   34.7   35.6
  10                                                                                                      

  Canadair CL 30.0          35.2   40.6   45.4   25            30   35   40   25.3          29.9   35.4   40.5
  44                                                                                                      

  CV 880 M    25.8          30.8   35.8   40.3   26            31   36   41   25.7          30.0   34.9   39.3

  MD-87       43.7          46.0   48.0   49.7   45            47   49   50   43.7          46.0   48.1   49.7

  DC-10-15    48.5          57.2   68.5   79.7   48            56   67   74   48.7          56.3   67.0   78.0

  IL76T       11.0          13.2   15.4   14.4   38            38   38   39   10.9          12.2   14.0   13.6

  L1011-1     44.3          51.7   61.7   72.2   45            52   62   73   46.3          51.9   61.1   71.3

  TU154B      17.5          23.8   30.4   36.2   19            25   32   38   15.8          18.2   23.6   29.0
  ----------- ------------- ------ ------ ------ ------------- ---- ---- ---- ------------- ------ ------ ------

[]{#__RefHeading___Toc9328145 .anchor}Table 5. ACNs for Selected
Aircraft on Flexible Pavements

  ----------- ---------- ------ ------ ------- ---------- ---- ---- ------ ---------- ------- ------- -------
  Aircraft    ACN by                           ACN by                      ACN by                     
  Type        COMFAA                           ICAO                        ACNF                       
                                               Design                      \[g.\]                     
                                               Man.                                                   

              Subgrade                         Subgrade                    Subgrade                   
              CBR                              CBR                         CBR                        

              15         10     6      3       15         10   6    3      15         10      6       3

  A310        35.9       39.7   48.1   63.2    36         40   48   64     35.80      39.73   48.11   63.18

  A320 DT     17.6       19.2   23.1   31.7    18         19   23   32     17.63      19.22   23.06   31.69

  Caravelle   14.7       16.5   19.3   23.1    15         17   19   23     13.88      15.49   18.72   22.89
  10                                                                                                  

  Canadair CL 31.5       35.6   40.3   48.1    27         30   36   47     31.52      35.61   40.27   48.13
  44                                                                                                  

  CV 880 M    26.5       30.6   35.7   44.0    27         31   36   44     26.53      30.62   35.77   43.98

  MD-87       38.6       41.1   46.0   49.2    39         42   46   50     37.89      39.13   42.59   46.42

  DC-10-15    55.8       61.5   73.4   100.2   55         61   72   100    55.39      60.85   72.15   98.88

  IL76T       9.0        10.4   12.5   16.5    37         40   45   53     8.23       9.31    10.90   13.96

  L1011-1     51.9       56.4   66.1   90.2    52         56   66   91     51.95      56.42   66.13   90.19

  TU154B      19.2       22.4   28.4   37.1    20         24   30   38     19.16      22.35   28.35   37.02
  ----------- ---------- ------ ------ ------- ---------- ---- ---- ------ ---------- ------- ------- -------

### ACN Numbers for C-17A on Rigid Pavements

In the case of the C-17A, COMFAA provides inconsistent results for ACNs
for rigid pavements on high and medium strength subgrades, as shown in
figure 6. Calculations of ACNs for rigid pavements use a rigid cutoff
value of 3, which is the standard for the ICAO computation of ACNs.
Increasing the value of the rigid cutoff gives consistent results, as
shown in table 6, but this procedure is not standard.

To fully understand the impact of changes in the rigid cutoff value on
ACNs, calculations of ACNs were made with different rigid cutoff values
for two types of gear loadings, as shown in figures 6 and 7. The ACNs
are presented in Tables 6 and 7. Table 6 presents ACNs for the C‑17A.
Table 7 presents ACNs for three out of six wheels of the C-17A. Tables 6
and 7 show that, for certain rigid cutoff values and certain subgrade
strengths, ACNs for both gear configurations can be identical. For
example, with a rigid cutoff value of 2 and a subgrade strength of 150
pci (40.7 kg/cm^3^), the ACN for both gear configurations is 57.7. For
the C-17A, an increase in the rigid cutoff value causes changes in ACNs
by the inclusion of additional wheels in the calculation of the ACNs. It
can be concluded that in the case of inconsistent ACN values for certain
gear configurations, consistency can be achieved by increasing the value
of the rigid cutoff.

[]{#__RefHeading___Toc9328146 .anchor}Table 6. ACNs for C-17A Aircraft
on Rigid Pavements

  -------------- -------- -------- -------- -------- -------- -------- --------
  k \[kg/cm^3^\] Rigid                                                 
                 Cutoff                                                

                 1        1.5      2        2.5      3        3.5      4

  150            38.0     56.9     57.7     57.7     53.5     45.0     43.5

  80             38.4     64.9     64.9     56.4     48.2     47.8     47.8

  40             71.5     71.6     62.4     56.7     56.7     56.7     56.7

  20             77.1     72.8     70.6     70.6     70.6     70.6     70.6
  -------------- -------- -------- -------- -------- -------- -------- --------

[]{#__RefHeading___Toc9328147 .anchor}Table 7. ACNs for Three out of Six
Wheels for C-17A Aircraft on Rigid Pavements

  -------------- -------- -------- -------- -------- -------- -------- --------
  k \[kg/cm^3^\] Rigid                                                 
                 Cutoff                                                

                 1        1.5      2        2.5      3        3.5      4

  150            38.0     56.9     57.7     57.7     57.7     57.7     57.7

  80             38.4     64.9     64.9     64.9     64.9     64.9     64.9

  40             71.5     71.6     71.6     71.6     71.6     71.6     71.6

  20             77.1     77.1     77.1     77.1     77.1     77.1     77.1
  -------------- -------- -------- -------- -------- -------- -------- --------

![](media/image5.png){width="4.5in" height="3.375in"}

[]{#__RefHeading___Toc12261921 .anchor}Figure 6. COMFAA Results for
C-17A Aircraft

![](media/image6.png){width="4.5in" height="3.375in"}

[]{#__RefHeading___Toc12261922 .anchor}Figure 7. COMFAA Results for
Three Wheels out of Six on C-17A Aircraft

### Slab Thickness Calculated Using COMFAA and AC 150/5320-6D

Seven cases were analyzed to compare the design thicknesses obtained
from COMFAA, AC 150/5320-6D, and R805FAA. The input data for these cases
are included in table 8. Table 9 presents a comparison of design
thicknesses obtained from the three sources. The last column in table 9
shows the difference between the design thickness obtained from R805FAA
and from COMFAA.

[]{#__RefHeading___Toc9328148 .anchor}Table 8. Input Data for Thickness
Designs

+---+------------+--------+------+--------+----+------+-----+------+
| N | Air        | Annual | P    | Covera | k  | Conc | G   | Tire |
| o | craft/Gear | Depa   | ass/ | ges^1^ |    | rete | ear | Con  |
| . | Con        | rtures | Cov. |        |    |      | Wei | tact |
|   | figuration |        | R    |        |    | Flex | ght | Area |
|   |            |        | atio |        |    | ural |     |      |
|   |            |        |      |        |    |      |     |      |
|   |            |        |      |        |    | Stre |     |      |
|   |            |        |      |        |    | ngth |     |      |
+---+------------+--------+------+--------+----+------+-----+------+
|   |            |        |      |        | lb | psi  | lbs | i    |
|   |            |        |      |        | /i |      |     | n^2^ |
|   |            |        |      |        | n^ |      |     |      |
|   |            |        |      |        | 3^ |      |     |      |
+---+------------+--------+------+--------+----+------+-----+------+
| 1 | Single     | 1200   | 5.18 | 4,633  | 1  | 750  | 35, | 29   |
|   | Wheel      |        |      |        | 00 |      | 625 | 6.87 |
+---+------------+--------+------+--------+----+------+-----+------+
| 2 | Dual Wheel | 1200   | 3.48 | 6,897  | 1  | 750  | 95, | 23   |
|   |            |        |      |        | 00 |      | 000 | 7.50 |
+---+------------+--------+------+--------+----+------+-----+------+
| 3 | Dual       | 6000   | 3.68 | 32,609 | 2  | 700  | 1   | 23   |
|   | Tandem     |        |      |        | 00 |      | 90, | 7.50 |
|   |            |        |      |        |    |      | 000 |      |
+---+------------+--------+------+--------+----+------+-----+------+
| 4 | A-300      | 6000   | 3.51 | 34,188 | 2  | 700  | 1   | 20   |
|   | Model B2   |        |      |        | 00 |      | 42, | 7.47 |
|   |            |        |      |        |    |      | 500 |      |
+---+------------+--------+------+--------+----+------+-----+------+
| 5 | B-747 SP   | 15000  | 3.70 | 81,081 | 50 | 800  | 1   | 21   |
|   |            |        |      |        |    |      | 66, | 0.00 |
|   |            |        |      |        |    |      | 250 |      |
+---+------------+--------+------+--------+----+------+-----+------+
| 6 | B-767      | 25000  | 3.90 | 1      | 3  | 650  | 1   | 20   |
|   |            |        |      | 28,205 | 00 |      | 42, | 2.46 |
|   |            |        |      |        |    |      | 500 |      |
+---+------------+--------+------+--------+----+------+-----+------+
| 7 | DC-10-10   | 25000  | 3.64 | 1      | 3  | 650  | 2   | 29   |
|   |            |        |      | 37,363 | 00 |      | 13, | 4.00 |
|   |            |        |      |        |    |      | 750 |      |
+---+------------+--------+------+--------+----+------+-----+------+

^1^Coverages are determined by multiplying annual departures by 20 and
dividing that product by the pass-to-coverage ratio \[b.\].

[]{#__RefHeading___Toc9328149 .anchor}Table 9. Results of Thickness
Designs

+----+---------------+-----+----------+-----------+-------------------+
| N  | Aircraft/Gear | Des |          |           | Difference        |
| o. | Configuration | ign |          |           | (inches)          |
|    |               | Th  |          |           |                   |
|    |               | ick |          |           | H~R805FAA~ -      |
|    |               | nes |          |           | H~COMFAA~         |
|    |               | s - |          |           |                   |
|    |               | H   |          |           |                   |
|    |               | (i  |          |           |                   |
|    |               | nch |          |           |                   |
|    |               | es) |          |           |                   |
+----+---------------+-----+----------+-----------+-------------------+
|    |               | 6D  | R805FAA  | COMFAA    |                   |
+----+---------------+-----+----------+-----------+-------------------+
| 1  | Single Wheel  | 1   | 10.00    | 9.98      | 0.02              |
|    |               | 0.2 |          |           |                   |
+----+---------------+-----+----------+-----------+-------------------+
| 2  | Dual Wheel    | 1   | 15.42    | 15.30     | 0.12              |
|    |               | 5.3 |          |           |                   |
+----+---------------+-----+----------+-----------+-------------------+
| 3  | Dual Tandem   | 1   | 16.99    | 16.65     | 0.34              |
|    |               | 7.0 |          |           |                   |
+----+---------------+-----+----------+-----------+-------------------+
| 4  | A-300 Model   | 1   | 12.96    | 12.72     | 0.24              |
|    | B2            | 3.0 |          |           |                   |
+----+---------------+-----+----------+-----------+-------------------+
| 5  | B-747 SP      | 1   | 17.55    | 17.43     | 0.12              |
|    |               | 7.8 |          |           |                   |
+----+---------------+-----+----------+-----------+-------------------+
| 6  | B-767         | 1   | 12.62    | 12.54     | 0.08              |
|    |               | 2.4 |          |           |                   |
+----+---------------+-----+----------+-----------+-------------------+
| 7  | DC-10-10      | 1   | 15.27    | 15.12     | 0.15              |
|    |               | 5.5 |          |           |                   |
+----+---------------+-----+----------+-----------+-------------------+

An additional investigation was conducted to see if there are any
differences between the design thicknesses calculated by AC 150/5320-6C
and those calculated by COMFAA. Overall, from tables 9 and 10, it can be
observed that the thicknesses calculated by the two methods are in
agreement. It can be concluded that COMFAA produces acceptable results.

[]{#__RefHeading___Toc9328150 .anchor}Table 10. Comparison of Design
Thicknesses Obtained by AC 150/5320-6C and COMFAA

+-------------------------+-----------+-----+-----+-----+-----+------+
| Major Input Data        | Tools     | Ann |     |     |     |      |
|                         |           | ual |     |     |     |      |
|                         |           | Pas |     |     |     |      |
|                         |           | ses |     |     |     |      |
|                         |           | (10 |     |     |     |      |
|                         |           | 00) |     |     |     |      |
+-------------------------+-----------+-----+-----+-----+-----+------+
|                         |           | 1.2 | 3.0 | 6.0 | 1   | 25.0 |
|                         |           |     |     |     | 5.0 |      |
+-------------------------+-----------+-----+-----+-----+-----+------+
| B-747-100, GW=800kp     | FAA-6C    | 1   | 1   | 1   | 14  | 14.4 |
|                         |           | 1.9 | 2.6 | 3.2 |     |      |
| R = 700psi, k=350 pci   |           |     |     |     |     |      |
+-------------------------+-----------+-----+-----+-----+-----+------+
|                         | ACNComp   | 1   | 1   | 1   | 1   | 14.3 |
|                         |           | 1.9 | 2.6 | 3.2 | 3.9 |      |
+-------------------------+-----------+-----+-----+-----+-----+------+
| DC-10-10, GW=400kp      | FAA-6C    | 1   | 1   | 16  | 1   | 17.3 |
|                         |           | 4.8 | 5.3 |     | 6.9 |      |
| R=800psi, k=50 pci      |           |     |     |     |     |      |
+-------------------------+-----------+-----+-----+-----+-----+------+
|                         | ACNComp   | 1   | 1   | 1   | 1   | 17.3 |
|                         |           | 4.4 | 5.3 | 6.0 | 6.8 |      |
+-------------------------+-----------+-----+-----+-----+-----+------+
| L1011-100, GW=500kp     | FAA-6C    | 1   | 1   | 1   | 15  | 15.5 |
|                         |           | 2.8 | 3.7 | 4.2 |     |      |
| R = 735 psi, k=100 pci  |           |     |     |     |     |      |
+-------------------------+-----------+-----+-----+-----+-----+------+
|                         | ACNComp   | 1   | 1   | 1   | 1   | 15.4 |
|                         |           | 2.8 | 3.6 | 4.2 | 4.9 |      |
+-------------------------+-----------+-----+-----+-----+-----+------+

## Analysis of Two Closely Spaced Triple Twin Tandems Using COMFAA

Figure 8 presents dimensions of two closely spaced triple twin tandems,
which are analyzed with COMFAA. The purpose of the analysis is to
determine the impact of a second triple twin tandem on the maximum slab
edge stress. The single tire load for the analyzed case is 58,852 pounds
(26,695 kg) and the tire pressure is 194 psi (1338 kPa).

Figures 9 and 10 show the results for two cases: Case 1 ― slab thickness
14.90 inches (37.85 cm), subgrade modulus k = 100 pci (27.1 kg/cm^3^),
and Case 2 ― slab thickness 12.62 inches (32.05 cm), subgrade modulus k
= 200 pci (54.3 kg/cm^3^).

Figures 9 and 10 show the contribution of each individual wheel to the
maximum slab edge stress at the bottom of the slab. In both cases, the
contribution of one triple twin tandem to the maximum slab edge stress
is significant, while the contribution of a second triple twin tandem is
negligible. It can be concluded that it is sufficient to consider only
one triple twin tandem when determining the maximum slab edge stress
using the H51 model.

The contribution of a single wheel to the edge stress, based on the
location of the wheel, is shown in figures 11 and 12. The wheel is
positioned perpendicular to the slab edge. The figures show that the
contribution of the wheel to the edge stress is insignificant when the
wheel is located more than 190 inches (482.6 cm) from the point of edge
stress evaluation.

[]{#__RefHeading___Toc12261923 .anchor}Figure 8. Two Closely Spaced
Triple Twin Tandems

[]{#__RefHeading___Toc12261924 .anchor}Figure 9. Contribution of
Individual Wheels to Slab Edge Stress at Location \"A\" for Two Triple
Twin Tandems (Slab Thickness = 14.90 inches (37.85 cm), k = 100 pci
(27.1 kg/cm^3^))

[]{#__RefHeading___Toc12261925 .anchor}Figure 10. Contribution of
Individual Wheels to Slab Edge Stress at Location \"A\" for Two Triple
Twin Tandems (Slab Thickness = 12.62 inches (32.05 cm), k = 200 pci
(54.3 kg/cm^3^))

![](media/image7.wmf)

[]{#__RefHeading___Toc12261926 .anchor}Figure 11. 3-D Surface of Edge
Stress Depending on Wheel Position at Coordinates x and y (Slab
Thickness = 12.62 inches (32.05 cm), k = 200 pci (54.3 kg/cm^3^))

![](media/image8.wmf)

[]{#__RefHeading___Toc12261927 .anchor}Figure 12. Surface Chart, Viewed
from Above, of Edge Stress Depending on Wheel Position at Coordinates x
and y (Slab Thickness = 12.62 inches (32.05 cm), k = 200 pci (54.3
kg/cm^3^))

# REFERENCES

a.  \"Aerodrome Design Manual: Part 3 Pavements,\" Second Edition, Doc.
    9157-AN/901, Part 3, International Civil Aviation Organization,
    1983.

b.  \"Airport Pavement Design and Evaluation,\" AC 150/5320-6D, July 7,
    1995.

c.  Kreger, W.C., \"Computerized Aircraft Ground Flotation
    Analysis-Edge-Loaded Rigid Pavement,\" General Dynamics Research
    Program, Task RDP 414-61-506, January 1967.

d.  Press, W.H., Flannery B.P., Teukolsky, S.A., and Vettering, W.T.,
    \"Numerical Recipes: The Art of Scientific Computing,\" Cambridge
    University Press, 1986.

e.  R805FAA Computer Program \"Computer Aided Design for Rigid Airport
    Pavements (R805FAA),\" U.S. Department of Transportation, Federal
    Aviation Administration, Washington, D.C., May 31, 1988.

f.  ACNR Computer Program \"ICAO Aircraft Classification Number (ACN)
    Analysis for Aerodrome Pavements,\" International Civil Aviation
    Organization (ICAO), Aerodromes, Air Routes and Ground Aids Section.

g.  ACNF Computer Program \"ICAO Aircraft Classification Number (ACN)
    Analysis for Aerodrome Pavements,\" International Civil Aviation
    Organization (ICAO), Aerodromes, Air Routes and Ground Aids Section.

[]{#__RefHeading___Toc9328113 .anchor}APPENDIX A  CHARACTERISTICS OF
AIRCRAFT ADDED TO COMFAA

<table>
<colgroup>
<col style="width: 3%" />
<col style="width: 16%" />
<col style="width: 13%" />
<col style="width: 9%" />
<col style="width: 8%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 0%" />
<col style="width: 6%" />
<col style="width: 7%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 5%" />
</colgroup>
<tbody>
<tr class="odd">
<td rowspan="3">No.</td>
<td rowspan="3">Aircraft Type</td>
<td rowspan="3">Wheel Arrangement</td>
<td colspan="2">Gear Load</td>
<td rowspan="3">Load on One Main Gear</td>
<td colspan="3">Tire Pressure</td>
<td colspan="4">Wheel Spacing</td>
</tr>
<tr class="even">
<td rowspan="2">kg</td>
<td rowspan="2">lbs</td>
<td rowspan="2">Mpa</td>
<td colspan="2" rowspan="2">psi</td>
<td colspan="2">Transverse</td>
<td colspan="2">Longitudinal</td>
</tr>
<tr class="odd">
<td>cm</td>
<td>in</td>
<td>cm</td>
<td>in</td>
</tr>
<tr class="even">
<td>1</td>
<td>A-310-200</td>
<td>Dual Tandem</td>
<td>132,000</td>
<td>291,010</td>
<td>0.467</td>
<td colspan="2">1.23</td>
<td>178</td>
<td>93</td>
<td>36.6</td>
<td>140</td>
<td>55.1</td>
</tr>
<tr class="odd">
<td>2</td>
<td>A-320 Dual Tandem</td>
<td>Dual Tandem</td>
<td>68,000</td>
<td>149,914</td>
<td>0.471</td>
<td colspan="2">1.12</td>
<td>162</td>
<td>78</td>
<td>30.7</td>
<td>100</td>
<td>39.4</td>
</tr>
<tr class="even">
<td>3</td>
<td>B720</td>
<td>Dual Tandem</td>
<td>104,326</td>
<td>229,999</td>
<td>0.474</td>
<td colspan="2">1</td>
<td>145</td>
<td>81</td>
<td>31.9</td>
<td>124</td>
<td>48.8</td>
</tr>
<tr class="odd">
<td>4</td>
<td>DC-3</td>
<td>Single</td>
<td>11,430</td>
<td>25,199</td>
<td>0.468</td>
<td colspan="2">0.31</td>
<td>45</td>
<td>-</td>
<td>-</td>
<td>-</td>
<td>-</td>
</tr>
<tr class="even">
<td>5</td>
<td>DC-4</td>
<td>Dual</td>
<td>33,113</td>
<td>73,002</td>
<td>0.468</td>
<td colspan="2">0.53</td>
<td>77</td>
<td>74</td>
<td>29.1</td>
<td>-</td>
<td>-</td>
</tr>
<tr class="odd">
<td>6</td>
<td>DC-8-43</td>
<td>Dual Tandem</td>
<td>144,242</td>
<td>317,999</td>
<td>0.465</td>
<td colspan="2">1.22</td>
<td>177</td>
<td>76</td>
<td>29.92</td>
<td>140</td>
<td>55.12</td>
</tr>
<tr class="even">
<td>7</td>
<td>DC-10-15</td>
<td>Dual Tandem</td>
<td>207,746</td>
<td>458,002</td>
<td>0.467</td>
<td colspan="2">1.34</td>
<td>194</td>
<td>137</td>
<td>53.9</td>
<td>163</td>
<td>64.2</td>
</tr>
<tr class="odd">
<td>8</td>
<td>MD-87</td>
<td>Dual</td>
<td>68,266</td>
<td>150,501</td>
<td>0.474</td>
<td colspan="2">1.17</td>
<td>170</td>
<td>71</td>
<td>28.0</td>
<td>-</td>
<td>-</td>
</tr>
<tr class="even">
<td>9</td>
<td>BAC 1-11 Series 400</td>
<td>Dual</td>
<td>39,690</td>
<td>87,501</td>
<td>0.475</td>
<td colspan="2">0.93</td>
<td>135</td>
<td>53</td>
<td>20.9</td>
<td>-</td>
<td>-</td>
</tr>
<tr class="odd">
<td>10</td>
<td>BAC 1-11 Series 475</td>
<td>Dual</td>
<td>44,679</td>
<td>98,500</td>
<td>0.475</td>
<td colspan="2">0.57</td>
<td>83</td>
<td>62</td>
<td>24.4</td>
<td>-</td>
<td>-</td>
</tr>
<tr class="even">
<td>11</td>
<td>Caravelle 10</td>
<td>Complex see Table 3</td>
<td>52,000</td>
<td>114,640</td>
<td>0.461</td>
<td colspan="2">0.75</td>
<td>109</td>
<td>40</td>
<td>15.7</td>
<td>107</td>
<td>42.1</td>
</tr>
<tr class="odd">
<td>12</td>
<td>Caravelle 12</td>
<td>Complex see Table 3</td>
<td>55,960</td>
<td>123,371</td>
<td>0.46</td>
<td colspan="2">0.88</td>
<td>128</td>
<td>41</td>
<td>16.1</td>
<td>107</td>
<td>42.1</td>
</tr>
<tr class="even">
<td>13</td>
<td>Canadair CL 44</td>
<td>Complex see Table 3</td>
<td>95,708</td>
<td>211,000</td>
<td>0.475</td>
<td colspan="2">1.12</td>
<td>162</td>
<td>51</td>
<td>20.1</td>
<td>122</td>
<td>48</td>
</tr>
<tr class="odd">
<td>14</td>
<td>CV 880 M</td>
<td>Dual Tandem</td>
<td>87,770</td>
<td>193,500</td>
<td>0.466</td>
<td colspan="2">1.03</td>
<td>149</td>
<td>55</td>
<td>21.7</td>
<td>114</td>
<td>44.9</td>
</tr>
<tr class="even">
<td>15</td>
<td>CV 990</td>
<td>Dual Tandem</td>
<td>115,666</td>
<td>255,000</td>
<td>0.485</td>
<td colspan="2">1.28</td>
<td>186</td>
<td>61</td>
<td>24.0</td>
<td>118</td>
<td>46.5</td>
</tr>
<tr class="odd">
<td>16</td>
<td>Dash 7</td>
<td>Dual</td>
<td>19,867</td>
<td>43,799</td>
<td>0.468</td>
<td colspan="2">0.74</td>
<td>107</td>
<td>42</td>
<td>16.5</td>
<td>-</td>
<td>-</td>
</tr>
<tr class="even">
<td>17</td>
<td><p>F27 Friendship</p>
<p>Mk500</p></td>
<td>Dual</td>
<td>19,777</td>
<td>43,601</td>
<td>0.475</td>
<td colspan="2">0.54</td>
<td>78</td>
<td>45</td>
<td>17.7</td>
<td>-</td>
<td>-</td>
</tr>
<tr class="odd">
<td>18</td>
<td><p>F28 Fellowship</p>
<p>Mk1000LPT</p></td>
<td>Dual</td>
<td>29,484</td>
<td>65,001</td>
<td>0.463</td>
<td colspan="2">0.58</td>
<td>84</td>
<td>58</td>
<td>22.8</td>
<td>-</td>
<td>-</td>
</tr>
<tr class="even">
<td>19</td>
<td><p>F28 Fellowship</p>
<p>Mk1000HTP</p></td>
<td>Dual</td>
<td>29,484</td>
<td>65,001</td>
<td>0.463</td>
<td colspan="2">0.69</td>
<td>100</td>
<td>55</td>
<td>21.7</td>
<td>-</td>
<td>-</td>
</tr>
<tr class="odd">
<td>20</td>
<td>Fokker 100</td>
<td>Dual</td>
<td>44,680</td>
<td>98,503</td>
<td>0.478</td>
<td colspan="2">0.98</td>
<td>142</td>
<td>59</td>
<td>23.2</td>
<td>-</td>
<td>-</td>
</tr>
<tr class="even">
<td>21</td>
<td>HS125</td>
<td>Dual</td>
<td>10,600</td>
<td>23,369</td>
<td>0.455</td>
<td colspan="2">0.77</td>
<td>112</td>
<td>32</td>
<td>12.6</td>
<td>-</td>
<td>-</td>
</tr>
<tr class="odd">
<td>22</td>
<td>HS748</td>
<td>Dual</td>
<td>21,092</td>
<td>46,500</td>
<td>0.436</td>
<td colspan="2">0.59</td>
<td>86</td>
<td>48</td>
<td>18.9</td>
<td>-</td>
<td>-</td>
</tr>
<tr class="even">
<td>23</td>
<td>IL62</td>
<td>Dual Tandem</td>
<td>162,600</td>
<td>358,472</td>
<td>0.47</td>
<td colspan="2">1.08</td>
<td>157</td>
<td>80</td>
<td>31.5</td>
<td>165</td>
<td>65</td>
</tr>
<tr class="odd">
<td>24</td>
<td>IL76T</td>
<td>Complex see Table 3</td>
<td>171,000</td>
<td>376,990</td>
<td>0.235</td>
<td colspan="2">0.64</td>
<td>93</td>
<td>-</td>
<td>-</td>
<td>258</td>
<td>101.6</td>
</tr>
<tr class="even">
<td>25</td>
<td>IL86</td>
<td>3 DT Units</td>
<td>209,500</td>
<td>461,868</td>
<td>0.312</td>
<td colspan="2">0.88</td>
<td>128</td>
<td>125</td>
<td>49.2</td>
<td>149</td>
<td>58.7</td>
</tr>
<tr class="odd">
<td>26</td>
<td>L-100-20</td>
<td>Tandem</td>
<td>70,670</td>
<td>155,801</td>
<td>0.482</td>
<td colspan="2">0.72</td>
<td>104</td>
<td>-</td>
<td>-</td>
<td>154</td>
<td>60.6</td>
</tr>
<tr class="even">
<td>27</td>
<td>Trident 1E</td>
<td>Complex see Table 3</td>
<td>61,160</td>
<td>134,835</td>
<td>0.46</td>
<td colspan="2">1.03</td>
<td>149</td>
<td>32</td>
<td>12.6</td>
<td>-</td>
<td>-</td>
</tr>
<tr class="odd">
<td>28</td>
<td>TU134A</td>
<td>Dual Tandem</td>
<td>47,600</td>
<td>104,940</td>
<td>0.456</td>
<td colspan="2">0.83</td>
<td>120</td>
<td>56</td>
<td>22.0</td>
<td>99</td>
<td>39</td>
</tr>
<tr class="even">
<td>29</td>
<td>TU154B</td>
<td>Complex see Table3</td>
<td>98,000</td>
<td>216,053</td>
<td>0.451</td>
<td colspan="2">0.93</td>
<td>135</td>
<td>62</td>
<td>24.4</td>
<td>98</td>
<td>38.6</td>
</tr>
<tr class="odd">
<td>30</td>
<td>VC10-1150</td>
<td>Dual Tandem</td>
<td>151,953</td>
<td>334,999</td>
<td>0.483</td>
<td colspan="2">1.01</td>
<td>146</td>
<td>86</td>
<td>33.9</td>
<td>155</td>
<td>61</td>
</tr>
</tbody>
</table>

[]{#__RefHeading___Toc9328114 .anchor}APPENDIX B  COMPARISON OF RESULTS
CALCULATED BY H51 FORTRAN AND VISUAL BASIC VERSIONS

**Listing B.1** TestH51 Input Data for A-300-600 Aircraft

[A-300-600]{.underline}

Runway Characteristics:

H K E MU RO DELTA

10 200 4000000 0.15 36.1354107661622 0

XLA, XLB, XLC, XLD = 27 0 65 0

XNA, XNB, XNC, XND = 2 1 2 1

Contact area of one tire = 232.427777777778 PHIE = 1.667

Inflation Pressure = 180 psi.

Gear Load = 167348 lb B = 150

**Listing B.2** TestH51 Input Data for B-777-200 Aircraft

[B-777-200]{.underline}

Runway Characteristics:

H K E MU RO DELTA

10 200 4000000 0.15 36.1354107661622 0

XLA, XLB, XLC, XLD = 56 0 65 0

XNA, XNB, XNC, XND = 2 1 3 1

Contact area of one tire = 491.758241758242 PHIE = 1.667

Inflation Pressure = 182 psi.

Gear Load = 537000 lb B = 150

**Listing B.3** TestH51 Input Data for IL76 Aircraft

[IL76]{.underline}

Runway Characteristics:

H K E MU RO DELTA

30 200 4000000 0.15 82.3709238474263 0

XLA, XLB, XLC, XLD = 24 56 58 0

XNA, XNB, XNC, XND = 2 2 2 1

Contact area of one tire = 320.245879120879 PHIE = 1.667

Inflation Pressure = 182 psi.

Gear Load = 466278 lb B = 150

Table B-1. Results for A-300-600 Aircraft

  ----- ----------- ------------ ---------------- ------------- ------------
  No.   Slab        GAMMA        Stress FORTRAN   Stress Vbasic Difference
        Thickness   (degree)     (psi)            (psi)         
        (in)                                                    

  1     10          0            1004.578         1004.575871   -0.000212%

  2                 60           1054.291         1054.288455   -0.000241%

  3                 90           945.305          945.3054643   0.000049%

  4     12          0            814.717          814.7168406   -0.000020%

  5                 60           833.604          833.6041241   0.000015%

  6                 90           755.909          755.9095996   0.000079%

  7     20          0            436.917          436.9165003   -0.000114%

  8                 60           426.846          426.8469253   0.000217%

  9                 90           397.995          397.9954854   0.000122%

  10    28          0            274.251          274.2508386   -0.000059%

  11                60           267.526          267.5260023   0.000001%

  12                90           255.716          255.7161598   0.000062%

  13    30          0            248.5            248.4995994   -0.000161%

  14                60           241.918          241.9179881   -0.000005%

  15                90           232.326          232.3262948   0.000127%
  ----- ----------- ------------ ---------------- ------------- ------------

Table B-2. Results for B-777-200 Aircraft

  ----- ----------- ------------ --------------- ------------- ------------
  No.   Slab        GAMMA        Stress FORTRAN  Stress Vbasic Difference
        Thickness   (degree)     (psi)           (psi)         
        (in)                                                   

  1     10          0            1220.749        1220.750891   0.000155%

  2                 60           1391.675        1391.674807   -0.000014%

  3                 90           972.494         972.491089    -0.000299%

  4     12          0            1021.577        1021.578512   0.000148%

  5                 60           1122.404        1122.402727   -0.000113%

  6                 90           866.44          866.4401079   0.000012%

  7     20          0            625.238         625.2371494   -0.000136%

  8                 60           624.298         624.2977675   -0.000037%

  9                 90           614.193         614.1912793   -0.000280%

  10    28          0            440.431         440.4310881   0.000020%

  11                60           426.891         426.8905455   -0.000106%

  12                90           458.038         458.0367487   -0.000273%

  13    30          0            406.216         406.2166814   0.000168%

  14                60           392.912         392.9105134   -0.000378%

  15                90           423.834         423.8327699   -0.000290%
  ----- ----------- ------------ --------------- ------------- ------------

Table B-3. Results for Il76 Aircraft

  ----- ----------- ------------ --------------- ------------- ------------
  No.   Slab        GAMMA        Stress FORTRAN  Stress Vbasic Difference
        Thickness   (degree)     (psi)           (psi)         
        (in)                                                   

  1     10          0            1009.358        1009.359067   0.000106%

  2                 60           1142.154        1142.155404   0.000123%

  3                 90           1061.429        1061.428613   -0.000036%

  4     12          0            887.207         887.207818    0.000092%

  5                 60           957.422         957.4172015   -0.000501%

  6                 90           891.804         891.8048697   0.000098%

  7     20          0            598.529         598.5295578   0.000093%

  8                 60           571.907         571.9084047   0.000246%

  9                 90           551.281         551.2808991   -0.000018%

  10    28          0            432.974         432.9747341   0.000170%

  11                60           397.195         397.1953286   0.000083%

  12                90           385.973         385.9738452   0.000219%

  13    30          0            399.173         399.1730765   0.000019%

  14                60           366.971         366.9717046   0.000192%

  15                90           357.659         357.6590433   0.000012%
  ----- ----------- ------------ --------------- ------------- ------------

[]{#__RefHeading___Toc9328115 .anchor}APPENDIX C  RIGID AND FLEXIBLE
PAVEMENT ACNS FOR AIRCRAFT ADDED TO COMFAA

Table C-1. ACNs for Added Aircraft on Rigid Pavements

<table>
<colgroup>
<col style="width: 3%" />
<col style="width: 19%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 8%" />
<col style="width: 5%" />
<col style="width: 5%" />
<col style="width: 5%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td rowspan="3">No.</td>
<td rowspan="3">Aircraft Type</td>
<td colspan="4">ACN by COMFAA</td>
<td colspan="4">ACN by ICAO Design Man.</td>
<td colspan="4">Difference in ACN Number</td>
</tr>
<tr class="even">
<td colspan="4">Subgrade k [MN/m<sup>3</sup>]</td>
<td colspan="4">Subgrade k [MN/m<sup>3</sup>]</td>
<td colspan="4">Subgrade k [MN/m<sup>3</sup>]</td>
</tr>
<tr class="odd">
<td>150</td>
<td>80</td>
<td>40</td>
<td>20</td>
<td>150</td>
<td>80</td>
<td>40</td>
<td>20</td>
<td>150</td>
<td>80</td>
<td>40</td>
<td>20</td>
</tr>
<tr class="even">
<td>1</td>
<td>A-310-200</td>
<td>32.4</td>
<td>38.7</td>
<td>46.2</td>
<td>53.2</td>
<td>33</td>
<td>39</td>
<td>46</td>
<td>54</td>
<td>-0.6</td>
<td>-0.3</td>
<td>0.2</td>
<td>-0.8</td>
</tr>
<tr class="odd">
<td>2</td>
<td>A-320 Dual Tandem</td>
<td>16.5</td>
<td>19.8</td>
<td>23.6</td>
<td>27.2</td>
<td>18</td>
<td>21</td>
<td>24</td>
<td>28</td>
<td>-1.5</td>
<td>-1.2</td>
<td>-0.4</td>
<td>-0.8</td>
</tr>
<tr class="even">
<td>3</td>
<td>B720</td>
<td>25.2</td>
<td>30.8</td>
<td>37.2</td>
<td>42.9</td>
<td>25</td>
<td>30</td>
<td>37</td>
<td>42</td>
<td>0.2</td>
<td>0.8</td>
<td>0.2</td>
<td>0.9</td>
</tr>
<tr class="odd">
<td>4</td>
<td>DC-3</td>
<td>6.0</td>
<td>6.5</td>
<td>6.9</td>
<td>7.2</td>
<td>6</td>
<td>7</td>
<td>7</td>
<td>7</td>
<td>0.0</td>
<td>-0.5</td>
<td>-0.1</td>
<td>0.2</td>
</tr>
<tr class="even">
<td>5</td>
<td>DC-4</td>
<td>13.2</td>
<td>14.9</td>
<td>16.6</td>
<td>17.9</td>
<td>13</td>
<td>15</td>
<td>17</td>
<td>18</td>
<td>0.2</td>
<td>-0.1</td>
<td>-0.4</td>
<td>-0.1</td>
</tr>
<tr class="odd">
<td>6</td>
<td>DC-8-43</td>
<td>41</td>
<td>49</td>
<td>57</td>
<td>65</td>
<td>40.7</td>
<td>48.7</td>
<td>57.1</td>
<td>64.6</td>
<td>0.3</td>
<td>0.3</td>
<td>-0.1</td>
<td>0.4</td>
</tr>
<tr class="even">
<td>7</td>
<td>DC-10-15</td>
<td>48.5</td>
<td>57.2</td>
<td>68.5</td>
<td>79.7</td>
<td>48</td>
<td>56</td>
<td>67</td>
<td>74</td>
<td>0.5</td>
<td>1.2</td>
<td>1.5</td>
<td>5.7</td>
</tr>
<tr class="odd">
<td>8</td>
<td>MD-87</td>
<td>43.7</td>
<td>46.0</td>
<td>48.0</td>
<td>49.7</td>
<td>45</td>
<td>47</td>
<td>49</td>
<td>50</td>
<td>-1.3</td>
<td>-1.0</td>
<td>-1.0</td>
<td>-0.3</td>
</tr>
<tr class="even">
<td>9</td>
<td>BAC 1-11 Series 400</td>
<td>24.8</td>
<td>26.2</td>
<td>27.5</td>
<td>28.5</td>
<td>25</td>
<td>26</td>
<td>28</td>
<td>29</td>
<td>-0.2</td>
<td>0.2</td>
<td>-0.5</td>
<td>-0.5</td>
</tr>
<tr class="odd">
<td>10</td>
<td>BAC 1-11 Series 475</td>
<td>22.6</td>
<td>24.8</td>
<td>26.8</td>
<td>28.4</td>
<td>22</td>
<td>25</td>
<td>27</td>
<td>28</td>
<td>0.6</td>
<td>-0.2</td>
<td>-0.2</td>
<td>0.4</td>
</tr>
<tr class="even">
<td>11</td>
<td>Caravelle 10</td>
<td>13.7</td>
<td>16.4</td>
<td>19.3</td>
<td>21.9</td>
<td>15</td>
<td>17</td>
<td>20</td>
<td>22</td>
<td>-1.3</td>
<td>-0.6</td>
<td>-0.7</td>
<td>-0.1</td>
</tr>
<tr class="odd">
<td>12</td>
<td>Caravelle 12</td>
<td>16.4</td>
<td>19.3</td>
<td>22.3</td>
<td>25.0</td>
<td>16</td>
<td>19</td>
<td>22</td>
<td>25</td>
<td>0.4</td>
<td>0.3</td>
<td>0.3</td>
<td>0.0</td>
</tr>
<tr class="even">
<td>13</td>
<td>Canadair CL 44</td>
<td>30.0</td>
<td>35.2</td>
<td>40.6</td>
<td>45.4</td>
<td>25</td>
<td>30</td>
<td>35</td>
<td>40</td>
<td>5.0</td>
<td>5.2</td>
<td>5.6</td>
<td>5.4</td>
</tr>
<tr class="odd">
<td>14</td>
<td>CV 880 M</td>
<td>25.8</td>
<td>30.8</td>
<td>35.8</td>
<td>40.3</td>
<td>26</td>
<td>31</td>
<td>36</td>
<td>41</td>
<td>-0.2</td>
<td>-0.2</td>
<td>-0.2</td>
<td>-0.7</td>
</tr>
<tr class="even">
<td>15</td>
<td>CV 990</td>
<td>40.4</td>
<td>47.3</td>
<td>54.1</td>
<td>59.9</td>
<td>41</td>
<td>48</td>
<td>54</td>
<td>60</td>
<td>-0.6</td>
<td>-0.7</td>
<td>0.1</td>
<td>-0.1</td>
</tr>
<tr class="odd">
<td>16</td>
<td>Dash 7</td>
<td>11.2</td>
<td>12.0</td>
<td>12.6</td>
<td>13.2</td>
<td>11</td>
<td>12</td>
<td>13</td>
<td>13</td>
<td>0.2</td>
<td>0.0</td>
<td>-0.4</td>
<td>0.2</td>
</tr>
<tr class="even">
<td>17</td>
<td><p>F27 Friendship</p>
<p>Mk500</p></td>
<td>9.9</td>
<td>10.9</td>
<td>11.7</td>
<td>12.3</td>
<td>10</td>
<td>11</td>
<td>12</td>
<td>12</td>
<td>-0.1</td>
<td>-0.1</td>
<td>-0.3</td>
<td>0.3</td>
</tr>
<tr class="odd">
<td>18</td>
<td><p>F28 Fellowship</p>
<p>Mk1000LPT</p></td>
<td>13.7</td>
<td>15.1</td>
<td>16.4</td>
<td>17.4</td>
<td>14</td>
<td>15</td>
<td>17</td>
<td>18</td>
<td>-0.3</td>
<td>0.1</td>
<td>-0.6</td>
<td>-0.6</td>
</tr>
<tr class="even">
<td>19</td>
<td><p>F28 Fellowship</p>
<p>Mk1000HTP</p></td>
<td>15.0</td>
<td>16.3</td>
<td>17.4</td>
<td>18.4</td>
<td>15</td>
<td>16</td>
<td>18</td>
<td>18</td>
<td>0.0</td>
<td>0.3</td>
<td>-0.6</td>
<td>0.4</td>
</tr>
<tr class="odd">
<td>20</td>
<td>Fokker 100</td>
<td>27.7</td>
<td>29.3</td>
<td>30.8</td>
<td>31.9</td>
<td>28</td>
<td>29</td>
<td>31</td>
<td>32</td>
<td>-0.3</td>
<td>0.3</td>
<td>-0.2</td>
<td>-0.1</td>
</tr>
<tr class="even">
<td>21</td>
<td>HS125</td>
<td>5.9</td>
<td>6.3</td>
<td>6.6</td>
<td>6.8</td>
<td>6</td>
<td>6</td>
<td>7</td>
<td>7</td>
<td>-0.1</td>
<td>0.3</td>
<td>-0.4</td>
<td>-0.2</td>
</tr>
<tr class="odd">
<td>22</td>
<td>HS748</td>
<td>9.6</td>
<td>10.5</td>
<td>11.3</td>
<td>11.9</td>
<td>10</td>
<td>11</td>
<td>11</td>
<td>12</td>
<td>-0.4</td>
<td>-0.5</td>
<td>0.3</td>
<td>-0.1</td>
</tr>
<tr class="even">
<td>23</td>
<td>IL62</td>
<td>41.6</td>
<td>50.1</td>
<td>59.7</td>
<td>68.6</td>
<td>42</td>
<td>50</td>
<td>60</td>
<td>69</td>
<td>-0.4</td>
<td>0.1</td>
<td>-0.3</td>
<td>-0.4</td>
</tr>
<tr class="odd">
<td>24</td>
<td>IL76T</td>
<td>11.0</td>
<td>13.2</td>
<td>15.4</td>
<td>14.4</td>
<td>38</td>
<td>38</td>
<td>38</td>
<td>39</td>
<td>-27.0</td>
<td>-24.8</td>
<td>-22.6</td>
<td>-24.6</td>
</tr>
<tr class="even">
<td>25</td>
<td>IL86</td>
<td>25.6</td>
<td>30.7</td>
<td>37.9</td>
<td>45.7</td>
<td>25</td>
<td>31</td>
<td>38</td>
<td>46</td>
<td>0.6</td>
<td>-0.3</td>
<td>-0.1</td>
<td>-0.3</td>
</tr>
<tr class="odd">
<td>26</td>
<td>L-100-20</td>
<td>30.2</td>
<td>32.7</td>
<td>35.5</td>
<td>38.2</td>
<td>30</td>
<td>33</td>
<td>36</td>
<td>38</td>
<td>0.2</td>
<td>-0.3</td>
<td>-0.5</td>
<td>0.2</td>
</tr>
<tr class="even">
<td>27</td>
<td>Trident 1E</td>
<td>31.8</td>
<td>34.3</td>
<td>36.5</td>
<td>38.4</td>
<td>32</td>
<td>34</td>
<td>37</td>
<td>39</td>
<td>-0.2</td>
<td>0.3</td>
<td>-0.5</td>
<td>-0.6</td>
</tr>
<tr class="odd">
<td>28</td>
<td>TU134A</td>
<td>10.3</td>
<td>12.6</td>
<td>15.2</td>
<td>17.7</td>
<td>11</td>
<td>13</td>
<td>16</td>
<td>19</td>
<td>-0.7</td>
<td>-0.4</td>
<td>-0.8</td>
<td>-1.3</td>
</tr>
<tr class="even">
<td>29</td>
<td>TU154B</td>
<td>17.5</td>
<td>23.8</td>
<td>30.4</td>
<td>36.2</td>
<td>19</td>
<td>25</td>
<td>32</td>
<td>38</td>
<td>-1.5</td>
<td>-1.2</td>
<td>-1.6</td>
<td>-1.8</td>
</tr>
<tr class="odd">
<td>30</td>
<td>VC10-1150</td>
<td>37.5</td>
<td>45.9</td>
<td>55.5</td>
<td>64.2</td>
<td>38</td>
<td>46</td>
<td>56</td>
<td>65</td>
<td>-0.5</td>
<td>-0.1</td>
<td>-0.5</td>
<td>-0.8</td>
</tr>
</tbody>
</table>

Table C-2. ACNs for Added Aircraft on Flexible Pavements

<table>
<colgroup>
<col style="width: 3%" />
<col style="width: 19%" />
<col style="width: 6%" />
<col style="width: 5%" />
<col style="width: 5%" />
<col style="width: 7%" />
<col style="width: 5%" />
<col style="width: 5%" />
<col style="width: 5%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td rowspan="3">No.</td>
<td rowspan="3">Aircraft Type</td>
<td colspan="4">ACN by COMFAA</td>
<td colspan="4">ACN by ICAO Design Manual</td>
<td colspan="4">Difference in ACN Number</td>
</tr>
<tr class="even">
<td colspan="4">Subgrade CBR</td>
<td colspan="4">Subgrade CBR</td>
<td colspan="4">Subgrade CBR</td>
</tr>
<tr class="odd">
<td>15</td>
<td>10</td>
<td>6</td>
<td>3</td>
<td>15</td>
<td>10</td>
<td>6</td>
<td>3</td>
<td>15</td>
<td>10</td>
<td>6</td>
<td>3</td>
</tr>
<tr class="even">
<td>1</td>
<td>A-310-200</td>
<td>35.9</td>
<td>39.7</td>
<td>48.1</td>
<td>63.2</td>
<td>36</td>
<td>40</td>
<td>48</td>
<td>64</td>
<td>-0.1</td>
<td>-0.3</td>
<td>0.1</td>
<td>-0.8</td>
</tr>
<tr class="odd">
<td>2</td>
<td>A-320 Dual Tandem</td>
<td>17.6</td>
<td>19.2</td>
<td>23.1</td>
<td>31.7</td>
<td>18</td>
<td>19</td>
<td>23</td>
<td>32</td>
<td>-0.4</td>
<td>0.2</td>
<td>0.1</td>
<td>-0.3</td>
</tr>
<tr class="even">
<td>3</td>
<td>B720</td>
<td>28.6</td>
<td>31.7</td>
<td>39.3</td>
<td>51.3</td>
<td>29</td>
<td>31</td>
<td>39</td>
<td>51</td>
<td>-0.4</td>
<td>0.7</td>
<td>0.3</td>
<td>0.3</td>
</tr>
<tr class="odd">
<td>4</td>
<td>DC-3</td>
<td>3.9</td>
<td>5.5</td>
<td>7.5</td>
<td>9.2</td>
<td>4</td>
<td>6</td>
<td>8</td>
<td>9</td>
<td>-0.1</td>
<td>-0.5</td>
<td>-0.5</td>
<td>0.2</td>
</tr>
<tr class="even">
<td>5</td>
<td>DC-4</td>
<td>12.3</td>
<td>14.0</td>
<td>16.5</td>
<td>20.4</td>
<td>11</td>
<td>14</td>
<td>16</td>
<td>20</td>
<td>1.3</td>
<td>0.0</td>
<td>0.5</td>
<td>0.4</td>
</tr>
<tr class="odd">
<td>6</td>
<td>DC-8-43</td>
<td>43</td>
<td>49</td>
<td>59</td>
<td>74</td>
<td>43.1</td>
<td>49.5</td>
<td>58.8</td>
<td>73</td>
<td>-0.1</td>
<td>-0.5</td>
<td>0.2</td>
<td>1.0</td>
</tr>
<tr class="even">
<td>7</td>
<td>DC-10-15</td>
<td>55.8</td>
<td>61.5</td>
<td>73.4</td>
<td>100.2</td>
<td>55</td>
<td>61</td>
<td>72</td>
<td>100</td>
<td>0.8</td>
<td>0.5</td>
<td>1.4</td>
<td>0.2</td>
</tr>
<tr class="odd">
<td>8</td>
<td>MD-87</td>
<td>38.6</td>
<td>41.1</td>
<td>46.0</td>
<td>49.2</td>
<td>39</td>
<td>42</td>
<td>46</td>
<td>50</td>
<td>-0.4</td>
<td>-0.9</td>
<td>0.0</td>
<td>-0.8</td>
</tr>
<tr class="even">
<td>9</td>
<td>BAC 1-11 Series 400</td>
<td>22.1</td>
<td>23.9</td>
<td>26.7</td>
<td>28.6</td>
<td>22</td>
<td>24</td>
<td>27</td>
<td>29</td>
<td>0.1</td>
<td>-0.1</td>
<td>-0.3</td>
<td>-0.4</td>
</tr>
<tr class="odd">
<td>10</td>
<td>BAC 1-11 Series 475</td>
<td>19.2</td>
<td>24.1</td>
<td>27.5</td>
<td>31.1</td>
<td>19</td>
<td>24</td>
<td>28</td>
<td>31</td>
<td>0.2</td>
<td>0.1</td>
<td>-0.5</td>
<td>0.1</td>
</tr>
<tr class="even">
<td>11</td>
<td>Caravelle 10</td>
<td>14.7</td>
<td>16.5</td>
<td>19.3</td>
<td>23.1</td>
<td>15</td>
<td>17</td>
<td>19</td>
<td>23</td>
<td>-0.3</td>
<td>-0.5</td>
<td>0.3</td>
<td>0.1</td>
</tr>
<tr class="odd">
<td>12</td>
<td>Caravelle 12</td>
<td>17.1</td>
<td>19.0</td>
<td>21.6</td>
<td>25.6</td>
<td>17</td>
<td>19</td>
<td>21</td>
<td>26</td>
<td>0.1</td>
<td>0.0</td>
<td>0.6</td>
<td>-0.4</td>
</tr>
<tr class="even">
<td>13</td>
<td>Canadair CL 44</td>
<td>31.5</td>
<td>35.6</td>
<td>40.3</td>
<td>48.1</td>
<td>27</td>
<td>30</td>
<td>36</td>
<td>47</td>
<td>4.5</td>
<td>5.6</td>
<td>4.3</td>
<td>1.1</td>
</tr>
<tr class="odd">
<td>14</td>
<td>CV 880 M</td>
<td>26.5</td>
<td>30.6</td>
<td>35.7</td>
<td>44.0</td>
<td>27</td>
<td>31</td>
<td>36</td>
<td>44</td>
<td>-0.5</td>
<td>-0.4</td>
<td>-0.3</td>
<td>0.0</td>
</tr>
<tr class="even">
<td>15</td>
<td>CV 990</td>
<td>39.9</td>
<td>45.7</td>
<td>53.0</td>
<td>64.0</td>
<td>40</td>
<td>45</td>
<td>53</td>
<td>64</td>
<td>-0.1</td>
<td>0.7</td>
<td>0.0</td>
<td>0.0</td>
</tr>
<tr class="odd">
<td>16</td>
<td>Dash 7</td>
<td>9.5</td>
<td>10.7</td>
<td>12.3</td>
<td>13.7</td>
<td>10</td>
<td>11</td>
<td>12</td>
<td>14</td>
<td>-0.5</td>
<td>-0.3</td>
<td>0.3</td>
<td>-0.3</td>
</tr>
<tr class="even">
<td>17</td>
<td><p>F27 Friendship</p>
<p>Mk500</p></td>
<td>7.9</td>
<td>9.8</td>
<td>11.6</td>
<td>13.4</td>
<td>8</td>
<td>10</td>
<td>12</td>
<td>13</td>
<td>-0.1</td>
<td>-0.2</td>
<td>-0.4</td>
<td>0.4</td>
</tr>
<tr class="odd">
<td>18</td>
<td><p>F28 Fellowship</p>
<p>Mk1000LPT</p></td>
<td>11.3</td>
<td>14.1</td>
<td>16.3</td>
<td>19.3</td>
<td>11</td>
<td>14</td>
<td>16</td>
<td>19</td>
<td>0.3</td>
<td>0.1</td>
<td>0.3</td>
<td>0.3</td>
</tr>
<tr class="even">
<td>19</td>
<td><p>F28 Fellowship</p>
<p>Mk1000HTP</p></td>
<td>12.9</td>
<td>15.0</td>
<td>17.2</td>
<td>19.7</td>
<td>13</td>
<td>15</td>
<td>17</td>
<td>20</td>
<td>-0.1</td>
<td>0.0</td>
<td>0.2</td>
<td>-0.3</td>
</tr>
<tr class="odd">
<td>20</td>
<td>Fokker 100</td>
<td>24.7</td>
<td>26.4</td>
<td>29.8</td>
<td>32.2</td>
<td>25</td>
<td>27</td>
<td>30</td>
<td>32</td>
<td>-0.3</td>
<td>-0.6</td>
<td>-0.2</td>
<td>0.2</td>
</tr>
<tr class="even">
<td>21</td>
<td>HS125</td>
<td>4.8</td>
<td>5.4</td>
<td>6.3</td>
<td>7.0</td>
<td>5</td>
<td>5</td>
<td>6</td>
<td>7</td>
<td>-0.2</td>
<td>0.4</td>
<td>0.3</td>
<td>0.0</td>
</tr>
<tr class="odd">
<td>22</td>
<td>HS748</td>
<td>7.7</td>
<td>9.5</td>
<td>10.9</td>
<td>13.0</td>
<td>8</td>
<td>9</td>
<td>11</td>
<td>13</td>
<td>-0.3</td>
<td>0.5</td>
<td>-0.1</td>
<td>0.0</td>
</tr>
<tr class="even">
<td>23</td>
<td>IL62</td>
<td>47.7</td>
<td>54.4</td>
<td>64.1</td>
<td>79.1</td>
<td>47</td>
<td>54</td>
<td>64</td>
<td>79</td>
<td>0.7</td>
<td>0.4</td>
<td>0.1</td>
<td>0.1</td>
</tr>
<tr class="odd">
<td>24</td>
<td>IL76T</td>
<td>9.0</td>
<td>10.4</td>
<td>12.5</td>
<td>16.5</td>
<td>37</td>
<td>40</td>
<td>45</td>
<td>53</td>
<td>-28.0</td>
<td>-29.6</td>
<td>-32.5</td>
<td>-36.5</td>
</tr>
<tr class="even">
<td>25</td>
<td>IL86</td>
<td>33.6</td>
<td>36.0</td>
<td>43.2</td>
<td>60.7</td>
<td>34</td>
<td>36</td>
<td>43</td>
<td>61</td>
<td>-0.4</td>
<td>0.0</td>
<td>0.2</td>
<td>-0.3</td>
</tr>
<tr class="odd">
<td>26</td>
<td>L-100-20</td>
<td>27.1</td>
<td>30.8</td>
<td>32.9</td>
<td>38.4</td>
<td>27</td>
<td>31</td>
<td>33</td>
<td>38</td>
<td>0.1</td>
<td>-0.2</td>
<td>-0.1</td>
<td>0.4</td>
</tr>
<tr class="even">
<td>27</td>
<td>Trident 1E</td>
<td>22.5</td>
<td>24.5</td>
<td>27.2</td>
<td>31.9</td>
<td>23</td>
<td>24</td>
<td>27</td>
<td>32</td>
<td>-0.5</td>
<td>0.5</td>
<td>0.2</td>
<td>-0.1</td>
</tr>
<tr class="odd">
<td>28</td>
<td>TU134A</td>
<td>11.5</td>
<td>12.5</td>
<td>15.3</td>
<td>20.0</td>
<td>12</td>
<td>13</td>
<td>16</td>
<td>21</td>
<td>-0.5</td>
<td>-0.5</td>
<td>-0.7</td>
<td>-1.0</td>
</tr>
<tr class="even">
<td>29</td>
<td>TU154B</td>
<td>19.2</td>
<td>22.4</td>
<td>28.9</td>
<td>37.1</td>
<td>20</td>
<td>24</td>
<td>30</td>
<td>38</td>
<td>-0.8</td>
<td>-1.6</td>
<td>-1.1</td>
<td>-0.9</td>
</tr>
<tr class="odd">
<td>30</td>
<td>VC10-1150</td>
<td>44.0</td>
<td>49.8</td>
<td>60.7</td>
<td>76.8</td>
<td>44</td>
<td>50</td>
<td>61</td>
<td>77</td>
<td>0.0</td>
<td>-0.2</td>
<td>-0.3</td>
<td>-0.2</td>
</tr>
</tbody>
</table>

[]{#__RefHeading___Toc9328116 .anchor}APPENDIX D  WHEEL ARRANGEMENT FOR
COMPLEX GEAR CONFIGURATIONS

  ------ -------------------------------- -----------------------------------------------------
  No.    Aircraft Type                    Wheel Arrangement

  11     Caravelle 10                     ![](media/image9.png){width="1.2291338582677165in"
                                          height="1.208267716535433in"}

  12     Caravelle 12                     ![](media/image10.png){width="1.208267716535433in"
                                          height="1.2602362204724409in"}

  13     Canadair CL 44                   ![](media/image11.png){width="1.208267716535433in"
                                          height="1.2602362204724409in"}

  24     IL76T                            ![](media/image12.png){width="1.5729166666666667in"
                                          height="1.4791666666666667in"}

  27     Trident 1E                       ![](media/image13.png){width="1.4375in"
                                          height="0.78125in"}

  29     TU154B                           
  ------ -------------------------------- -----------------------------------------------------