Anti-missile systems will be installed on three passenger planes flying in and out of New York's John F. Kennedy International Airport to test how they function on busy commercial routes.

While the military has used the systems successfully, airlines have baulked at putting them on passenger planes, citing fears about higher energy costs and delays from malfunctions.

The devices, which cost US$500,000 to US$1 million each, protect planes from shoulder-fired missiles by sending out light beams to redirect a missile's path. But their high cost - one study estimated a price tag of US$11 billion to equip 6,800 American-flagged planes - combined with airline resistance has produced legislative deadlock.

Shoulder-fired missiles "are out there, but there are a lot of other things to worry about", one government official said.

Democrat congressman Steve Israel, who has pressed the Government to install countermeasures, praised the tests. He noted that El Al Israel Airlines and British Airways had fitted civilian planes with anti-missile systems.

"We have the technology to protect our planes," he said, "but critics have posed questions about their suitability for commercial aircraft. The only way to see if the systems work on commercial aircraft is to try them on commercial aircraft."

The threat is deemed so significant that in 2005 the New York Police Department built a tabletop exercise around the scenario of a jet being shot out of the sky after take-off from Kennedy. Officials declined to discuss what countermeasures were instituted as a result.

The new tests, on three planes owned by American Airlines, will look at whether the devices increase fuel use and how they withstand the wear and tear of daily use, said Homeland Security Department spokeswoman Amy Kudwa. Under the US$29 million contract with London-based BAE Systems, data will be collected during 11,000 kilometres of flying time.

Another anti-missile aircraft defence system, designed by Northrop Grumman Corporation, is being tested on FedEx cargo planes. Ms Kudwa said the Homeland Security Department would not make a recommendation but would forward test results to Congress.

Estimates of the number of shoulder-fired missiles around the world vary from 350,000 to 500,000, with older models selling for as little as US$300, according to one report. No US commercial plane has ever been shot down.

The most recent confirmed attack was on a cargo plane hit while taking off from Baghdad in 2003. The plane managed to land safely. In 2002, two missiles narrowly missed a packed Israeli charter jet taking off from Mombasa, Kenya. By early 2006, all government-owned El Al planes were equipped with countermeasures.