ILS Simultaneous Landings
Not to get too technical but there are a few different types of ILS approaches. Many airports have two or three parallel ILS approaches. In order to get more airplanes to land, certain procdures were developed.
ILS approaches to parallel runways are divided into three classes depending on runway centerline separation as well as ATC procedures and capabilities: Dependent Parallel, and Independent Parallel. The Independent has two types: Simultaneous Parallel and Simultaneous Close Parallel.
Dependent Parallel ILS approaches may be conducted to parallel runways with centerlines at least 2,500 feet apart. The aircraft are also separated by at least 1.5 NM diagonally. This gives you one aircraft to the left, then one to the right and so on…On average, 29 arrivals per hour for each runway.
Independent Parallel ILS approaches are conducted with centerlines separated by 4,300 to 9,000 feet apart and these do not required diagonal separation. This gives you one aircraft to each runway at the same tme which allows more aircraft to land. On average, 58 arrivals per hour for each runway.
There is also a dedicated final controller who monitors the space between the two ILS approaches called the No Transgression Zone (NTZ). If the plane on the left drifts into the NTZ, then the aircraft on the right is vectored away to avoid a possible collision.
The Simultaneous Close Parallel ILS approaches are conducted with centerlines separated less than 4,300 feet apart. Minneapolis International (MSP) was one of the first to use this system.
The ILS-PRM (Precision Runway Monitor) uses advance radar that updates very quickly and is able to predict an aircrafts position 10 seconds ahead of time. When a plane drifts near the NTZ, both a visual and audio alarm go off and ATC can quickly issue breakout instructions to fly away from danger. While flying this type of approach, the flight crew talks to tower on one frequency and monitors a separate frequency that the radar controller will talk on if needed.
Any aircraft can fly an ILS-PRM approach as long as your airplane has Dual VHF Communications. There is a 20-minute video the FAA developed which quickly goes through the ILS-PRM procedures. The local FAA office (FSDO) may be able to get a copy for you.
Remember when sex was safe and flying was dangerous?