Shift from radar to GPS should make tracking faster and more accurate, allowing more planes in the air. From a report: Since World War II, air-traffic controllers have used radar to keep track of aircraft. But as of Jan. 1, most planes and helicopters flying in the U.S. must be equipped with transponders that allow their movements to be traced with GPS coordinates. The deadline caused a flurry of upgrades last year as operators who hadn't yet complied with the mandate rushed to equip their aircraft in time. Now, more than 100,000 commercial and general aviation aircraft have the transponders, according to the Federal Aviation Administration, including nearly all commercial aircraft and an estimated 60% of general aviation aircraft that need it. "If you're flying an antique plane in the middle of Ohio, you don't have to have it," said John Zimmerman, vice president of Sporty's Pilot Shop, an Ohio retailer and flight school. The U.S. controls 29.4 million square miles of airspace, including all of the U.S., large portions of the Atlantic and Pacific oceans and the Gulf of Mexico. The FAA mandate primarily applies to Class A airspace, which is 18,000 feet or more above sea level; Class B airspace, the areas surrounding the nation's busiest airports; Class C airspace, the areas around smaller regional airports; and above 10,000 feet in Class E, the most common airspace. LaGuardia Airport in New York is Class B. Richmond International Airport in Virginia is Class C.Read more of this story at Slashdot. Click here to read full news..