Skip to Main Content
At least 43 major airports in the US have parallel runways that are in very close proximity to each other - less than 4,400 feet apart. During visual meteorological conditions (VMC), when visual contact between aircraft is possible, airport capacity is greatly increased by having aircraft fly closely spaced parallel visual approaches. Under instrument meteorological conditions (IMC), airports with runways closer than 4,400 feet are required to revert to a single runway operation or to run dependent approaches. Each of these traffic flows greatly reduces the number of landing aircraft, sometimes by as much as 50%. This study examined the operational implementation of an airborne system which would support closely spaced parallel approach operations at airports with parallel runway center lines as close as 2,500 feet during IMC. Additionally, the study examined the system's requirements, both flight deck and ATC, that would support the implementation of closely spaced parallel approach operations at a major HUB airport. The primary objective of the AILS (airborne instrument landing system) concept is to enable safe independent approaches to parallel runways with runway spacing of at least 2,500 feet, through the development of concepts, procedures, and supporting technology.