Airspace System

Precision landing systems, which allow aircraft to land and depart under poor weather conditions, improve airline safety and increase runway capacity. During the 1970s, the Federal Aviation Administration (FAA) began developing the microwave landing system to replace the current instrument landing system, which has been in use for more than 50 years. FAA expects the microwave landing system to be ready by the mid-1990s. In the years since the decision was made to develop the microwave landing system, however, other technologies for precision landing systems have emerged, and FAA is now supporting the development of a satellite-based system, as well as an instrument landing system enhanced with a computer-based flight management system. This report reviews these systems. GAO (1) describes the capabilities and costs of these precision landing systems and (2) identifies some potential consequences of FAA's approach to developing them.

GAO found that: (1) the current instrument landing system (ILS) cannot be adapted to use enhanced systems features, is limited in coverage area, cannot be used in all locations, and is sensitive to signal interference; (2) ILS, with a flight management system (ILS/FMS), permits some but not all enhancements, and has all other ILS limitations; (3) the microwave landing system (MLS) meets the full range of operational requirements for precision landing systems, but it may not be fully used by the aviation industry because of the availability of other systems and the cost of installing instrumentation; (4) FAA is developing a satellite-based navigation system that could potentially provide all the capabilities of the other systems plus airport surface and air route navigation, service to all runways within an airport, and service to both ends of the runway; (5) the satellite system will require technically challenging enhancements for a precision landing system; (6) FAA estimates that the cost of maintaining, replacing, and adding new ILS equipment will be $360.9 million between 1992 and 2000, and users' costs will range from $3,600 for general aviation aircraft to $107,00 for some commercial aircraft; (7) FAA costs for ILS/FMS include maintenance of ILS ground stations, procedures development costs, and certification of FMS equipment, and users will spend between $500,000 and $750,000 for FMS packages plus certification costs; (8) FAA costs for MLS include those for ILS, plus $2.6 billion for development, procurement and installation, and additional costs for increased staffing, certification of on-board instrumentation, and lighting systems; (9) the satellite system's costs are not directly comparable because the system will perform functions beyond just precision landings; and (10) the Department of Defense will spend $10 billion for development and implementation of the satellites and FAA will spend up to $315.8 million for ground stations and additional funds for developing approach procedures and equipment certification.

Recommendations

Our recommendations from this work are listed below with a Contact for more information. Status will change from "In process" to "Open," "Closed - implemented," or "Closed - not implemented" based on our follow up work.

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