A Tool for Estimating Airport Access Benefits from GPS-Based Instrument Approaches

The MITRE Corporation developed a computer-based tool that estimates the Height Above Touchdown (HAT) and visibility minima for Global Positioning System (GPS) instrument approaches using electronic databases of terrain and obstacles. The model uses criteria from the U.S. Federal Aviation Administration (FAA) Terminal Instrument Procedures (TERPS) developed for GPS approaches, but can be modified to use different criteria. The design of the model allows the evaluation of a large number of runways, with subsequent analysis of the benefits of a particular approach procedure. The development of wide area systems to augment the GPS has long promised the capability of providing or improving the instrument approach capability at many airports. In particular, one of the objectives of the Wide Area Augmentation System (WAAS) is to provide, where possible, straight-in instrument approaches with vertical guidance to all instrument capable runways in the USA. There are over 5000 airports in CONUS that have at least one runway over 3000 ft long. At present, the minima for approaches with vertical guidance that would result from the development of WAAS are known for only a few runways. Using the present FAA approach design apparatus to estimate the minima for all the possible runways would be an impossibly long task. Application of the MITRE Corporation computer model enables a timely high-level evaluation of HAT estimates for a large number of runway ends, and will eventually include considerations for airport infrastructure. This paper provides a statistical summary of preliminary results showing HAT and visibility benefits for approaches to a large number of airports in the USA, and also provides a comparison of approach minima between different classes of augmented GPS approaches. The intent of the analysis is to assist in the final design criteria for GPS approaches in the USA.