This program is designed to follow the letter of the law in defining takeoff and landing field lengths. The other main reference for this program is the collection of Federal Aviation Administration Regulations, as many of the procedures coded here are spelled out in the regulations. You can read these regulations by going to the FAA Site and following the link to Federal Aviation Regulations under the heading Regulations and Guidelines. From there, you want Current Federal Aviation Regulations and follow this on to Part 25 for Commercial Transport Aircraft. This computer program is in accordance with the regulations as of June 1979, but I cannot guarantee its current conformance.