In aviation, precision runway monitor (PRM) is a high-speed, high-precision radar system developed by Raytheon to monitor simultaneous close parallel instrument approaches to airports. PRM is one type of radar system that can be used to allow simultaneous approaches on parallel runways that are spaced less than 1,310 metres (4,300 ft) to each other. Airports at which PRM is in use in the United States include Chicago-O'Hare, San Francisco, Detroit, and Atlanta. Internationally only Sydney, Australia uses PRM.