the most precise and accurate approaches. A runway with an ILS can accommodate 29 arrivals per hour. ILS systems on two or three runways increase capacity with parallel (dependent) ILS, simultaneous parallel (independent) ILS, precision runway monitor (PRM), and converging ILS approaches. ILS approaches have three classifications, CAT I, CAT II, and CAT III. CAT I SA, CAT II and CAT III require additional certification for operators, pilots, aircraft and equipment, with CAT III used mainly by air carriers and the military. Simultaneous parallel approaches require runway centerlines to be between 4,300 and 9,000 feet apart, plus a "dedicated final monitor controller" to monitor aircraft separation. Simultaneous close parallel (independent) PRM approaches must have runways separation to be between 3,400 and 4,300 feet. Simultaneous offset instrument approaches (SOIAs) apply to runways separated by 750–3,000 feet. A SOIA uses an ILS/PRM on one runway and an LDA/PRM with glideslope for the other. VOR approach These approaches use VOR facilities on and off the airport and may be supplemented with DME and TACAN. NDB approach These approaches use NDB facilities on and off the airport and may be supplemented with a DME. These approaches are gradually being phased out in Western countries. Radar approach This will be either a precision approach radar (PAR) or an airport surveillance radar (ASR) approach. Information is published in tabular form. The PAR provides vertical and lateral guidance plus range. The ASR only provides heading and range information. Airborne radar approach This is a rare type of approach, where a radar installed on the approaching aircraft is used as the primary means of navigation for the approach. It is mainly used at offshore oil platforms and select military bases. This type of approach takes advantage of the fact that the runway or more commonly, the oil platform stands out from its surrounding environment when viewed on a radar. For additional visibility on a radar, radar reflectors may be installed alongside the runway. Localizer approach These approaches include a localizer approach, localizer/DME approach, localizer back course approach, and a localizer-type directional aid (LDA). In cases where an ILS is installed, a back course may be available in conjunction with the localizer. Reverse sensing occurs on the back course using standard VOR equipment. With a horizontal situation indicator (HSI) system, reverse sensing is eliminated if it is set appropriately to the front course. Simplified directional facility (SDF) approach This