WASHINGTON (CNN) -- In first-ever tests for commercial airplanes carrying passengers, as many as three American Airlines jets will be equipped with a shoulder-fired missile defense system.
The Department of Homeland Security signed a $29 million contract with BAE Systems on December 21.
BAE said Thursday it is working with American Airlines to put laser systems on the planes, which will be flying between New York and California.
Since the contract calls for the planes to log about 7,000 flight hours, the tests will probably last from early spring, starting in March or April, until the end of the year, DHS spokeswoman Amy Kudwa said.
The systems have already been tested on cargo aircraft and out-of-service passenger planes. The new contract calls for the systems to be tested for the first time on aircraft carrying passengers.
DHS, American Airlines and BAE Systems were all careful to assure there will be no test firing -- through simulators or otherwise. The tests primarily will check the systems' worthiness in air and their maintenance reliability.
The system works by detecting the heat-seeking missiles and then emitting a laser that diverts the missile.
Homeland Security officials say there is no specific threat of these weapons -- also known as MANPADS, for Man-Portable Air Defense Systems -- being fired at planes.
Taliban forces, however, successfully used MANPADS against Soviet helicopters in Afghanistan. Terrorists tried, unsuccessfully, in 2002 to shoot down an Israeli passenger jet in Kenya with them. Insurgents hit a DHL cargo plane in Baghdad the following year, but the plane landed safely.
Experts say about 500,000 to 700,000 MANPADS have been produced worldwide, and some have been purchased in Middle Eastern and Central Asian arms markets for as little as $5,000.
Since 2003, Congress has pressured DHS to adapt military anti-MANPADS technology to commercial aviation. Commercial airlines have opposed efforts to install defense systems, which are costly, add weight, and can weaken the plane's aerodynamics.
A chief goal of the testing program is to discover how to increase the systems' endurance. Military systems require frequent maintenance -- not practical for commercial airplanes that fly for extended periods between maintenance checks.
American Airlines on Thursday said it is participating in the program, but added it is "not in favor of installing counter-MANPADS on commercial aircraft."
The airline believes protection is best accomplished by preventing terrorists from getting shoulder-fired missiles, or by using ground-based systems, spokesman John Hotard said.
But the airline said it is willing to participate because it "wants to understand the development" of these technologies that might be available in the future.
Last year, American and BAE installed and test flew BAE's hardware on a Boeing 767 that was not in commercial service, Hotard said. E-mail to a friend 
All About Air Travel • U.S. Department of Homeland Security
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