Microwave Landing Systems

Pursuant to a congressional request, GAO reviewed the Federal Aviation Administration's (FAA) National Airspace System Plan, focusing on: (1) the justification and requirements for replacing improved instrument landing systems (ILS) with microwave landing systems (MLS); (2) potential MLS operational and economic benefits; (3) the MLS siting strategy; and (4) industry and user association views of ILS and MLS.

GAO found that FAA: (1) first justified its need for MLS in 1969, citing concerns about ILS reliability and limitations and projected large increases in air traffic volume; (2) planned to replace ILS with MLS, although it did not reassess its needs by taking into consideration substantial ILS improvements and lower-than-projected traffic volumes; (3) experienced significant delays and increased program costs for MLS production and testing; (4) has not adequately assessed potential MLS benefits or identified its limitations; (5) requested $20 million to initiate a second MLS procurement and to develop the avionics to demonstrate MLS benefits; (6) is developing plans to test MLS at two airports; and (7) developed its list of MLS implementation sites without considering test results, cost benefits, and user support. GAO also found that: (1) both national and international air carriers were generally satisfied with ILS capabilities; (2) regional and commuter airlines generally supported MLS; and (3) commercial and general aviation pilots' views toward MLS differed.

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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