Chet Aero Marine

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Software and Spreadsheets for Airfield Design

Note: this site, and have offered software developed by the U.S. Government for free. Unfortunately a good deal of this software has “gone commercial,” putting it out of reach for many users (especially student.) The Federal Aviation Administration has bucked this trend, and for this we are thankful. The software below is 32-bit Windows software unless otherwise stated. Download and use of the software subject to the terms and conditions of this website.

Also note: except for the spreadsheets, all of the files are in .zip format. Included in the zip file is the documentation and supplementary files and information. Source code not included due to server size limitations.

BAKFAA – Computer Program for Back Calculation of Airport Pavement Properties

We have two earlier versions: the full binary and setup programs for one and another earlier version as well.

Operating System: BAKFAA is a 32-bit program and requires Windows 95/98, NT, or later. System requirements will vary depending upon the version being used.

BAKFAA is the FAA software to perform backcalculation of pavement material properties using Heavy Weight Deflectometer/Falling Weight Deflectometer (HWD/FWD) data.

1.  Designed as a .Net application

         •  Compatible with all existing versions of .Net environment
         •  Runs under Windows XP, Windows Vista, Windows 7, Windows 8, and Windows 10

2.  Ability to process a file in a Batch Mode

         •  Can process any number of deflection records at a time
         •  Exports batch calculation results into .csv files
         •  Presents a graph of batch calculation results

3.  Ability to switch application interface between English and Metric Units System

         •  All internal application calculations and calls to LEAF module are still using English Units System
         •  All application content (text, lists and graphs) is presented depending on Units System choice
         •  Application is capable of processing data input files (excluding LEAFAircraft.Ext) in both systems
         •  Application output files can be presented in both systems

4.  Extended list of possible file formats

5.  File Conversion Feature

         •  Converts a proprietary manufacturer’s file into PDDX (Pavement Deflection Data Exchange) format file .ddx

6.  Joint Transfer Efficiency Feature

         •  Calculates distribution of deflections across rigid pavement airfield joints

DOS Program Compilation

If you need help running DOS programs, click here

This is a collection of four DOS programs:

  • 3DAAP: The Three-Dimensional Airspace Analysis Program (3DAAP) is software developed for use as an analysis tool to study airspace constraints to vertical development on and off the airport property boundary. It provides a set of tools to construct, depict, and analyze airspace restricting surfaces including Federal Aviation Regulation (FAR) Part 77.25 Imaginary Surface analysis, obstruction shadow diagramming, line of sight analysis and navigational aid siting criteria. It also provides different methods to determine conflicts within the airspace surfaces and objects or structures on the ground.
  • Airport Design (for Microcomputers): This augments Advisory Circular (AC) 150/5060-5, Airport Capacity and Delay, including Changes 1 and 2, AC 150/5300-13, Airport Design, including Changes 1 through 4, and AC 150/5325-4A, Runway Length Requirements for Airport Design.
  • GEO83: This is a collection of geodetic calculation programs, using the North American Datum of 1983 (NAD83), for individuals involved in airspace studies. GEO83 is composed of input information for new users and five geodetic programs. Both written and graphic descriptions for the programs are provided below. The INPUT/OUTPUT data and the results calculated by the programs are boxed in the examples for easy identification.
  • MU41A: A program to estimate runway friction.

Spreadsheets for Pavement Design

Two Microsoft Excel spreadsheets for design of the following:


An older version of this software is here.

COMFAA is a program for computing flexible and rigid Aircraft Classification Numbers (ACNs) and pavement thickness. The FAA does not officially support the program as a standard nor sanction any use of the results. A help file is included which gives brief information on the capabilities of the program and how to use the various features. It would probably be useful to print the help file for reference as there is no other documentation describing operation of the program. An additional report describes the procedures used to compute pavement strength and thickness.

The external aircraft file contains the landing gears used as examples in the ICAO pavement design manual. English units are used throughout.

The ACNs are computed using the International Civil Aviation Organization (ICAO) methodology. It is not an official FAA standard, specification or regulation, nor is it intended as a substitute for official guidance on reporting ACNs contained in ICAO publications. It is believed that the ACNs computed by this program are generally consistent with those reported by ICAO for specific aircraft, but in the event of conflict, the latter shall be considered authoritative.

In 1997, ICAO’s ACN-PCN Study Group recommended that an interim alpha factor of 0.72 at 10,000 coverages be used for computing ACN for 6-wheeled landing gears.

By default, the ACN values for 6-wheel aircraft gear configuration including the Boeing B-777 airplane are computed using this interim modified alpha factor. The standard ACN cutoff for rigid pavement stress computation is 3 times the radius of relative stiffness (rrs). This gives inconsistent results with large complex gear configurations such as the C-17 (high-strength ACN higher than low-strength ACN). An option is therefore provided to change the cut-off. This sometimes leads to numerical problems and the numerical procedure may not converge.

Flexible pavement thickness design with COMFAA follows the same methodology used to produce the thickness design charts published in FAA AC 150/5320-6. That is, for a given subgrade CBR and a given number of coverages for the design aircraft, total pavement thickness is computed by the “CBR” method. The user has to determine the design aircraft and make the conversion from aircraft departures to design aircraft coverages. Conversion of layer thicknesses with appropriate equivalency factors must also be done by the user.

Rigid pavement thickness design with COMFAA follows the same methodology used to produce the thickness design charts published in FAA AC 150/5320-6. That is, for a given modulus of subgrade reaction and a given number of coverages for the design aircraft, total pavement thickness is computed by the Westergaard edge stress method with FAA failure criteria. The user has to determine the design aircraft and make the conversion from aircraft departures to design aircraft coverages. Conversion of support layers to effective modulus of subgrade reaction must also be done by the user.


FAARFIELD 2.0 is the FAA’s standard software for airport pavement thickness design and evaluation (AC 150/5320-6G, Airport Pavement Design and Evaluation) and pavement strength reporting using the ACR/PCR method (AC 150/5335-6D, Standardized Method of Reporting Pavement Strength – PCR). FAARFIELD 2.0 features include:

  • A completely redesigned graphical user interface (GUI) with improved screen flow and explorer-based navigation.
  • A new 3D finite element computational library, FAASR3D (FAA Structural Response – 3D), written in Visual Basic.NETTM.
  • Support for the new ICAO ACR-PCR system.
  • New graphical vehicle editor provides the ability to add, save and edit user-defined vehicles.
  • Updated aircraft library.
  • Ability to work with multiple jobs/sections at once.


  • FAARFIELD stands for FAA Rigid and Flexible Iterative Elastic Layered Design. FAARFIELD 2.0 incorporates full 3D finite element responses to aircraft loads (for new rigid pavements and rigid overlays). The 3D finite element models used for rigid pavement designs are computationally intensive and may result in long run times, depending on the computer characteristics. We would appreciate your comments concerning this program and your suggestions on how it could be improved.
  • FAARFIELD 2.0 runs on WindowsTM operating systems. Windows 7 or higher is recommended. Please follow installation instructions in the readme file.
  • Point of contact: For questions, comments or further information concerning this program, please contact Dr. David R. Brill, FAA Airport Technology R&D Branch, ANG-E262.


We have an earlier version here.

FEAFAA (Finite Element Analysis – FAA) was developed by the FAA Airport Technology R&D Branch as a stand-alone tool for 3D finite element analysis of multiple-slab rigid airport pavements and overlays. It is useful for computing accurate responses (stresses, strains and deflections) of rigid pavement structures to individual aircraft landing gear loads. FEAFAA is not intended for use as an FAA design procedure. For performing pavement thickness designs in conformance with FAA standards, please download FAARFIELD 1.305.

FEAFAA makes use of the 3D finite element program NIKE3D, originally developed by the U.S. Dept. of Energy Lawrence Livermore National Laboratory (LLNL). This program has been modified by the FAA for pavement analysis and is distributed according to terms of a Software Agreement between the FAA and LLNL. 

Note: Minimum requirements to run FEAFAA 2.0 are Windows XP or higher with 512MB of RAM. However, it is recommended that you have Windows 7 or higher with 4.0 GB of RAM for best performance. FEAFAA 2.0 is compiled to run on 32-bit or 64-bit operating systems.

For further information, please contact Dr. David R. Brill


FEDFAA is a computer program for airport pavement thickness design. It implements both layered elastic based and 3D finite element-based design procedures developed under the sponsorship of the Federal Aviation Administration (FAA) for new and overlay design of flexible and rigid pavements. The layered elastic procedures, as implemented in the program, are the FAA airport pavement thickness design standards referenced in Chapter 7 of Advisory Circular AC 150/5320-6D, change 3. The core of the program is a structural response module consisting of two programs, LEAF and NIKE3D (version 3.3.2.FAA.1.0). LEAF is a layered elastic computational program implemented, in this case, as a Microsoft Windowsô dynamic link library written in Visual Basic.NETô. NIKE3D version 3.3.2.FAA.1.0 is 3D finite element computational program, written in Visual Fortran and linked to the main program through a dynamic-link library. The remainder of the program is written in Visual Basic.Net and operates under Microsoft Windows. Both LEAF and NIKE3D are loaded and executed by FEDFAA when needed and are not visible to the user.Design information is entered by means of two graphical screens, one for the structure and one for the traffic. Default values and ranges for the various input parameters have been set so that the designs produced by FEDFAA are compatible with designs produced by the design procedures in Chapter 3 of AC 150/5320-6D for aircraft up to and including the current generation (B-727, DC-8, B-747, DC-10, etc.). Designs for new generation aircraft having triple-dual-tandem (TDT) landing gear, such as the B-777, are not covered by the design procedures in Chapter 3 of AC 150/5320-6D. Chapter 7 of AC 150/5320-6D, in conjunction with FEDFAA, provides the necessary information for thickness design when TDT aircraft are included in the aircraft mix.

Apart from the procedures being implemented as a computer program instead of as nomographs, the main change in pavement design from the user’s perspective is that the “design aircraft” concept has been replaced by design for fatigue failure expressed in terms of a “cumulative damage factor” (CDF) using Miner’s rule. Also, the major material property of the pavement layers is now uniformly expressed as an elastic modulus instead of the previous CBR (California Bearing Ratio) for flexible pavements or k value for rigid pavements. Formulas for transforming CBR and k values to modulus values are provided where appropriate in the documentation. Automatic conversion is provided in the program.

It should also be borne in mind that, although layered elastic based procedures, and 3D finite element models, are normally considered to be mechanistic, and more rational than the previous procedures, a considerable amount of engineering judgement is still required. Designs produced by FEDFAA should comply with the detailed requirements and recommendations of AC 150/5320-6D. The program does not automatically satisfy all of these requirements and the recommendations in the AC should be followed in the selection of input parameters. It is the designer’s responsibility to use the program and the advisory circular in conjunction with each other.

A complete description of the design procedures and program structure is not possible within the confines of a user’s manual, and these descriptions can be found in other publications. The main intent of the user’s manual is to provide sufficient information for operating the program, selecting input data values, and interpreting the output data. Installation of the program is described first, followed by descriptions of the various parts of the program and its operation. Information is then given on the structure data input requirements and how they relate to the design procedures. Final sections provide a short discussion on program running times, with possible strategies for decreasing design time for a given design case, a description of the structure of external data files so that interested users can access the files and incorporate the data in other applications if desired, and a selection of design examples.

The relationship between the layered elastic and 3D finite element based thickness design procedures and the nomograph based thickness design procedures in Chapter 3 of AC 150/5320-6D is not discussed in the manual. However, it should be pointed out that the traffic and failure models are fundamentally different and comparisons between the two sets of procedures are only valid when considering multiple aircraft traffic mixes. Single aircraft comparisons misleadingly indicate a degree of conservatism with the LED procedures which is not present for typical multiple aircraft mixes. The program is also primarily intended for use in designing airport pavements according to a standard procedure. It is not intended to be used to compare the damaging effects of different aircraft by running single aircraft designs or CDF computations, i.e., ACN type calculations.


ICAO-ACR calculates ICAO aircraft classification rating (ACR) numbers for aircraft operating on flexible and rigid airport pavements. The method follows the proposed amendment to ICAO Annex 14 replacing the current ACN-PCN system with ACR-PCR. The ACR system is similar in concept to ACN, with the following major differences:

  • All structures are layered elastic (rigid and flexible). Alpha factors are not used.
  • Retains 4 standard subgrade categories, but defined by modulus E (not CBR or k).
  • Flexible ACR considers all wheels in the main landing gear.
  • Standard tire pressure increased to 1.5 MPa.
  • Standard coverages increased to 36,500 for flexible ACR.
  • Derived single wheel load (DSWL) is expressed in 100’s (not 1000’s) of kg.

Note that ACR numerical values are approximately one order of magnitude higher than the equivalent ACN. This is intentional, to prevent confusion between the two systems.

ICAO-ACR runs a Visual Basic.NET dynamic-link library (DLL) called ACRClassLib.dll.  ACRClassLib.dll can be linked directly to other programs that either compute ACR directly, or that use the ACR computation to evaluate PCR. Technical information on linking the library to a calling program is given in the document User Information for ICAO-ACR.

At this time, ICAO-ACR is not an official FAA or ICAO standard.


ICAO-ACN calculates ICAO aircraft classification numbers (ACN) for aircraft operating on flexible and rigid airport pavements. The flexible pavement ACNs are calculated using the CBR method of thickness design at standard CBR values of 15, 10, 6 and 3.  Alpha factors follow the revised schedule of alpha factors adopted by ICAO in a State Letter dated October 16, 2007. The rigid pavement ACNs are calculated using the PCA method thickness design at standard k-values of 150.0, 80.0, 40.0 and 20.0 MN/m3.  ICAO-ACN 1.0 is based on the computer program COMFAA 3.0 that accompanies AC 150/5335-5C, “Standardized Method of Reporting Pavement Strength – PCN.” However, ICAO-ACN 1.0 is not an official FAA or ICAO standard at this time.


LEDFAA 1.3 is a Computer Program for Airport Pavement Thickness Design. It is a 32-bit version and requires Windows 95/98, NT, or later. Setup requires the files:

  • Setup.exe
  • Setup.lst

Copy all of the files into a directory on a hard disk. Then run setup.exe.

The Alternate SG check box allows a flexible pavement design (or Life) to be run based on the vertical strain at the top of the layer below the arrow on the left side of the pavement structure. The procedure is:

  1. get into the Structure window
  2. check the Alternate SG box at the bottom left of the structure
  3. press the Modify button
  4. click to the left of the picture of the structure (in the margin) to move the arrow so that it sits to the left of the layer above the layer where the vertical strain criterion will be applied
  5. return to design mode
  6. if a design is run then the layer pointed to by the arrow will change thickness to satisfy the strain criterion in the layer below
  7. if Life is run then the life for the strain criterion in the layer below will be calculated.

See the help file under Running the Program – Options for information on Batch, No AC CDF, and No Out Files.

LEDFAA 1.3 includes the Airbus A340-500 and A340-600 aircraft in the aircraft library. The same methodology is used as for other aircraft with two wing gear and one belly gear (MD-11 and A340-200 for example) except that the A340-500/600 has a dual-tandem belly gear instead of a dual-wheel belly gear. The methodology is for the A340-500/600 to be split into two separate aircraft for design; one with the two wing gear and the other with the one belly gear. The two aircraft (for design) are shown separately in the aircraft list.

LEDFAA 1.3 includes the Airbus A380-800 and A380-800F aircraft in the aircraft library. Inclusion of these aircraft required changes to the design methodology implemented in version 1.2 because of the different number of wheels in the wing and body gears (four in the wing and six in the body). The main difference is in the flexible design procedure as follows:

  1. 1. Vertical strain at the top of the subgrade is computed at multiple points with all of the wheels in the main gear contributing to the computed strain (16 wheels for the B-747 and 20 wheels for the A-380). In version 1.2, subgrade strain is computed for the B-747 with four wheels, representing only one of the gears, contributing to the computed strain.
  2. 2. Response under the wing and body gears is evenly split into two areas. The maximum response in the wing gear area is used to compute the pass-to-coverage ratios and cumulative damage factors (CDF) for the wing gears. The maximum response in the body gear area is used to compute pass-to-coverage ratios and CDFs for the body gears. These two sets of CDF values are then added to the CDFs calculated for all of the other aircraft in the mix and the result used in the normal thickness design procedure.

The design procedure for rigid pavement design is unchanged from that in LEDFAA 1.2. The difference between the number of wheels in the wing and body gears of the A-380 is accommodated by treating the aircraft as two different aircraft in the design mix. One of the design mix aircraft is a dual tandem with the same configuration as the A-380 wing gears and the other is a dual-tridem with the same configuration as the body gears of the A-380. The separation into two design mix aircraft is transparent to the user.

A number of other changes have been made to the program either for ease of use or for improved functionality. These changes include:

  1. Replacement of the layered elastic computational program Julea with the internally prepared program Leaf.
  2. A full 32-bit implementation which is compatible with all current Microsoft PC operating systems.
  3. The default setting for data output files (*.out) is for them not to be written. Double click on the gray area of the Structure Window and uncheck “No Out Files” for the data files to be written to the working directory. (The default setting is not described in the help file.)

LEDFAA 1.3 is an interim release of the computer program, FAArfield, now in preparation. FAArfield includes a 3-D FEM model for rigid pavement response calculations. The flexible design procedure will remain unchanged from LEDFAA 1.3 except that the failure model parameters may be adjusted as a result of the compatibility study now underway. Any changes in the flexible design parameters will result in minor differences in computed design thicknesses.


FAA PAVEAIR is a web-based airport pavement management system that provides users with historic and current information about airport pavement construction, maintenance and management.


The Federal Aviation Administration’s computer program for computing pavement elevation profile roughness indexes.


Transverse grooves in an airport pavement allow water to be ejected from beneath the tires of an aircraft moving at high speed. It has been found that the grooves can efficiently reduce the hydroplaning potential of a pavement during wet weather.

In the automatic device measurement of grooves, a laser sensor from a truss profiler constantly detected the distance between the grooved surface and an initial standard line as the aircraft tires repeatedly passed through the grooved areas. A special airport pavement groove identification program, ProGroove was developed to obtain the results of groove geometric parameters.

The ProGroove calculation is performed by comparing the vertical distance between individual profile data points with the corresponding low-pass filtered and bridging filtered data points. If their differences exceed the given threshold for a number of consecutive times, the first exceeded point is considered as the start point of a potential groove. Then, the end point of the potential groove is localized as the difference moves back to less than the given threshold. The groove depth is obtained from the difference between the top of the groove and the bottom of the groove. The top of groove value is determined from an average of the two maximum points of the groove which are the highest point on the left side and the right side of the groove. The bottom of groove value is simply taken as the lowest point of a groove, that is, the lowest point between the two maximum points of an individual groove.

ProGroove software was developed by Visual Basic .Net using Windows Presentation Foundation (WPF) interface. The program can remove the groove-like disturbances of joints in concrete pavements from the counted grooves and provides the groove number, location, depth and width, as well as a series of statistical results for groove quality analysis.

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