WASHINGTON  Tens of thousands of airline passengers will soon be flying on jets outfitted with anti-missile systems as part of a new government test aimed at thwarting terrorists armed with shoulder-fired projectiles. Three American Airlines Boeing 767-200s that fly daily round-trip routes between New York and California will receive the anti-missile laser jammers this spring, according to the Department of Homeland Security, which is spending $29 million on the tests. Jets will fly with the jammer device mounted on the belly of the plane, between the wheels. The device works with sensors, also mounted on the plane, that detect a heat-seeking missile and shoot a laser at it to send the missile veering harmlessly off course. Anti-missile systems have been tested on cargo planes. But "this is the first time these systems have been tested on actual passenger airlines in commercial service," says Burt Keirstead, director of commercial aircraft protection at BAE Systems, which developed the anti-missile device. "It's the ultimate consumer use of the equipment." Officials emphasize that no missiles will be test-fired at the planes, which will fly between New York's John F. Kennedy International Airport and the international airports in Los Angeles and San Francisco. The purpose of the tests is to determine how well the laser-jamming technology works on routine flights, how the devices affect fuel consumption and how much maintenance they require, according to Keirstead. Although there has not been an attempt to take down a jet on U.S. soil with a shoulder-fired missile, Homeland Security has warned about the possibility because the portable, lightweight weapons can be bought on the black market for as little as a few hundred dollars. There have been numerous deadly attacks on military jets and cargo planes overseas, and several near collisions with passenger planes. In 2002, two shoulder-fired missiles narrowly missed an Israeli airliner jet as it took off with 261 passengers in Mombassa, Kenya. The Defense Department uses laser-jamming technology on its planes, but using the systems on commercial airliners is much more controversial because of concerns about cost and maintenance. "If this is going to break down every other month vs. every fifth year, obviously that's a big, big difference," says Jim Tuttle of the Homeland Security Department's Science and Technology division. Keirstead says the systems could be installed for somewhere from $500,000 to $1 million per plane, but it's unclear how much it would cost to maintain them. Airlines have balked at paying the cost, and Congress would have to decide whether the federal government would foot the bill. American Airlines spokesman John Hotard says company officials agreed to participate in the tests in case Congress eventually requires airlines to install the devices. But American is "philosophically opposed" to anti-missile technology on commercial planes, he says. "When you look at the cost benefit, it would be an extremely expensive proposition, and in the end, is it really going to work?" Enlarge By Robert Hanashiro, USA TODAY Three American Airlines passenger jets will be fitted with anti-missile systems this spring to test how the devices affect fuel consumption and how much maintenance they require. Conversation guidelines: USA TODAY welcomes your thoughts, stories and information related to this article. Please stay on topic and be respectful of others. Keep the conversation appropriate for interested readers across the map.