WASHINGTON: US anti-missile technology is still too costly to install on America's passenger airlines to guard against Al Qaeda using shoulder-fired missiles to shoot down the planes, according to a study on Tuesday.

Laser-based jammer technology, used mainly in military aircraft to thwart shoulder-fired missile attacks, is not yet practical to use on commercial air planes, said the study by RAND Corp., a non-profit research organization.

The report said it would cost about $11 billion plus about $2.1 billion a year in operational costs to install missile counter-measures on the nation's 6,800 commercial aircraft.

"Given the significant costs involved with operating counter-measures based upon current technology, we believe a decision to install such systems aboard commercial airliners should be postponed until the technologies can be developed and shown to be more compatible in a commercial environment," RAND said in its report.

"Al Qaeda and its affiliates have both the motive and the means to bring down US commercial aircraft with shoulder-fired missiles," the study said. "No such attempt has yet been made against a US carrier, but given the measures being taken to preclude 9/11-style attacks, the use of (shoulder-fired missiles) will unavoidably become more attractive to terrorists," it said, referring to the Sept 11, 2001 hijacked plane attacks by Al Qaeda on the United States that killed 3,000 people.

RAND researchers found many unresolved questions about how the anti-missile systems would operate on commercial airlines, including issues such as the number of false alarms and whether attackers could find ways to circumvent the safeguards.

Last year the US Department of Homeland Security awarded $45 million contracts each to Northrop Grumman Corp. and BAE Systems Plc to design separate proposals to re-engineer the military system so anti-missile systems could be used on passenger aircraft. A Homeland Security spokesman said the defence companies were about one-third finished with the effort. -Reuters