The F-16 was a type of fighter jet used by the United States Air Force.
As soon as Syed Ali confessed that Second Wave's nuclear weapon was being launched from Norton Airfield, CTU Los Angeles director George Mason ordered Michelle Dessler to redirect two F-16s over the airport, in the event the terrorists managed to get it off the ground in a plane. ("Day 2: 7:00pm-8:00pm")
General Walsh at Edwards Air Force Base scrambled F-16s to intercept one of Dmitri Gredenko's aerial drones, which had been launched from the Shadow Valley carrying one of the stolen suitcase nukes. As the drone was passing between satellite grids, CTU lost its position, so Walsh ordered the planes to wait in a holding pattern until it was rediscovered. ("Day 6: 7:00pm-8:00pm")
The Air Force scrambled an F-16 to intercept Global Skies Airlines Flight 117, which had been cut off from Northeast Air Traffic Control and was being fed false landing vectors by Tony Almeida. However, the jet was thirteen minutes out, too long before the flight was due to land at JFK International Airport. ("Day 7: 9:00am-10:00am")