Microwave Landing System: 1976

As soon as it was possible to join the new inventions of the airplane and the radio in a practical way, it was done. Pilots found themselves "flying the beam” to navigate from one city to another and lining up with the runway, even in poor visibility, using the Instrument Landing System (ILS). ILS could tell the pilots if they were left or right of the runway centerline and if they were higher or lower than the established glide slope during the final approach. ILS required straight-in approaches and separation between aircraft, which limited the number of land­ings allowed each hour at the busiest airports. To improve upon this, the FAA, NASA, and the Department of Defense (DOD) in 1971 began developing the Microwave Landing System (MLS), which promised,

among other things, to increase the frequency of landings by allowing multiple approach paths to be used at the same time. Five years later, the FAA took delivery of a prototype system and had it installed at the FAA’s National Aviation Facilities Experimental Center in Atlantic City, NJ, and at NASA’s Wallops Flight Research Facility in Virginia.[210]

Between 1976 and 1994, NASA was actively involved in understand­ing how MLS could be integrated into the national airspace system. Configuration and operation of aircraft instrumentation,[211] pilot proce­dures and workload,[212] air traffic controller procedures,[213] use of MLS with helicopters,[214] effects of local terrain on the MLS signal,[215] and the deter­mination to what extent MLS could be used to automate air traffic con­trol[216] were among the topics NASA researchers tackled as the FAA made plans to employ MLS at airports around the Nation.

But having proven with NASA’s Applications Technology Satellite program that space-based communication and navigation were more than feasible (but skipping endorsement of the use of satellites in the FAA’s 1982 National Airspace System Plan), the FAA dropped the MLS program in 1994 to pursue the use of GPS technology, which was just beginning to work itself into the public consciousness. GPS signals, when enhanced by a ground-based system known as the Wide Area Augmentation System (WAAS), would provide more accurate position information and do it in a more efficient and potentially less costly man­ner than by deploying MLS around the Nation.[217]

Although never widely deployed in the United States for civilian use, MLS remains a tool of the Air Force at its airbases. NASA has

employed a version of the system called the Microwave Scan Beam Landing System for use at its Space Shuttle landing sites in Florida and California. Moreover, Europe has embraced MLS in recent years, and an increasing number of airports there are being equipped with the system, with London’s Heathrow Airport among the first to roll it out.[218]