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New Developments in FAA Airport Pavement
Thickness Design Software
Gordon F. Hayhoe
FAA William J. Hughes Technical Center
Airport Technology Research and Development Branch
AAR-410
Atlantic City International Airport, NJ 08405
(609) 485-8555, gordon.hayhoe@faa.gov
Izydor Kawa
Galaxy Scientific Corporation
2500 English Creek Ave., Bldg. C
Egg Harbor Twp., NJ 08234-5562
(609) 645-0900, izydor.kawa@galaxyscientific.com
David R Brill
FAA William J. Hughes Technical Center
Airport Technology Research and Development Branch
AAR-410
Atlantic City International Airport, NJ 08405
(609) 485-5198, david.brill@faa.gov
1
ABSTRACT
The Federal Aviation Administration (FAA) has upgraded its LEDFAA airport pavement design software. LEDFAA
version 1.2 was released in 1995 as part of FAA Advisory Circular 150/5320-16. The new program, LEDFAA
version 1.3, is a full 32-bit implementation which is compatible with the latest Microsoft® operating systems. The
user interface and data entry procedures have been updated somewhat, including the addition of an option to change
to metric units and an option to change the evaluation layer for flexible pavements. A new layered elastic
computational program written in Visual Basic® replaces the FORTRAN program used in version 1.2. Two changes
have been made to the flexible pavement design procedure. First, in the failure model (subgrade strain versus
coverages), allowable strain is now independent of subgrade modulus, additional data points for six-wheel gears
have been added, and the slope of the model is shallower at high coverages than at low coverages. Second, for
multiple-gear aircraft, such as the B-747 and the A380, subgrade strain is now computed with all of the wheels in
the main landing gear contributing to the strain computation. The rigid pavement design procedure is unchanged.
The changes are described in detail and future developments discussed.
INTRODUCTION
LEDFAA is a computer program for the thickness design of airport pavements. The program is currently referenced
in Federal Aviation Administration (FAA) Advisory Circular AC 150/5320-16, “Airport Pavement Design for the
Boeing 777 Airplane” (1). Appendix 2 of AC 150/5320-16 is a user’s manual for the program and is repeated in the
LEDFAA help file. AC 150/5320-16 is intended to be used in conjunction with AC 150/5320-6D, “Airport
Pavement Design and Evaluation” (2), and adds requirements specific to operation of the B-777 aircraft as well as
outlining changes to the requirements of AC 150/5320-6D related to the use of LEDFAA for thickness design. AC
150/5320-16 and LEDFAA functionally replace the following paragraphs of Advisory Circular AC 150/5320-6D:
• 304. Determination of Design Aircraft.
• 305. Determination of Equivalent Annual Departures by the Design Aircraft.
• 316. [Flexible Pavement] Design Curves.
• 332. a. Rigid Pavement Design Curves.
• 405. Hot Mix Asphalt Overlays on Existing Flexible Pavement.
• 406. Hot Mix Asphalt Overlay on Existing Rigid Pavement.
• 410. Concrete Overlay on Flexible Pavement.
• 411. Concrete Overlay on Rigid Pavement.
• 412. Bonded Concrete Overlays.
The design aircraft and annual departure equivalency procedures presented in paragraphs 304 and 305 are
replaced in LEDFAA by a cumulative damage factor (CDF) procedure. Paragraph 316 presents the thickness design
curves for new flexible and asphalt overlays on flexible pavements. These curves are based on the CBR method of
design (see, for example, references 2 and 3) and are replaced in LEDFAA by a layered elastic based methodology
which uses vertical strain at the top of the subgrade as a predictor of structure life (reference 4). Paragraph 332 a.
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