Pilots flying to Dallas/Fort Worth International Airport and San Diego Lindbergh Field might notice unusual runway status lights that warn of possible conflicting traffic. The systems have been in place since 2005 at DFW and 2006 at Lindbergh, but the FAA recently awarded contracts to upgrade the status light test systems and to install them at more airports with complex configurations.

The systems consist of  “a series of runway lights, not unlike traffic lights,” according to the FAA, “that tell pilots whether or not runways are clear.” The system uses information from ASDE-X and AMASS surveillance systems to detect whether aircraft or vehicles are on or near runways and calculates possible conflicts. At runway entrances and takeoff hold positions, in-pavement lights illuminate to warn pilots not to cross or enter the runway or to take off. At Daugherty Field, in Long Beach, Calif., the FAA is testing a final approach runway occupancy signal system, which flashes a light to warn landing pilots that there is a problem on the runway and they should not land.