Al Qaeda and its terror affiliates have the motive and the means to bring down U.S. commercial aircraft with shoulder-fired missiles, but spending billions to create countermeasures against the missiles "doesn't appear appropriate," a study has found.

The Rand Corporation (search), in a 64-page report issued Tuesday, found that the use of Man Portable Air Defense Systems (MANPADS) will become more attractive to terrorists, and said Al Qaeda (search) relishes the opportunity to bring down American commercial aircraft full of passengers, preferably in daylight and in cities that are major media hubs.

Read the report by clicking here (pdf).

Last year, Deputy Homeland Security Secretary Asa Hutchinson said during a teleconference that there was a specific threat of MANPADS being used to launch attacks on jetliners, but he stressed that the timing of his announcement did not reflect any specific concern.

On Tuesday, a Homeland Security official told FOX News there is no credible information that domestic flights are being threatened.

In November 2003, a DHL cargo flight was forced to make an emergency landing in Baghdad after being hit by a surface-to-air missile. That same month, terrorists linked to Al Qaeda fired two missiles at an Israeli passenger plane taking off from an airport in Kenya. Both missiles missed their target.

The Rand report said that to prevent such an attack, a multi-layered approach for securing the airlines is needed. But it also concluded that putting anti-missile defenses on planes is far too expensive.

“If we decide as a nation to significantly increase spending on homeland security, then spending this much on anti-missile systems may be appropriate,” James Chow, a RAND engineer who headed the project, said in a statement. “But given what we spend today, a large investment in technology still unproven in commercial airlines doesn't appear appropriate.”

Equipping 6,800 U.S. commercial jetliners with laser countermeasures would cost $11 billion, plus an additional $2.1 billion annual operating cost, the report found. By way of comparison, the federal government currently spends about $4.4 billion annually on all transportation security.

Over 20 years, the cost to develop, procure and operate these systems would amount to an estimated $40 billion.

Homeland Security officials have been looking at the issue of shoulder-fired missiles for more than a year. The department is investigating the problem through two channels:

  • A broad interagency task force is looking at increased security measures at airports as well as “buy back” programs to take the missiles out of circulation. Officials estimate that 700,000 MANPADS are in existence but they don’t know how many are not accounted for.

  • The department is looking at ways to take current military technology to detect shoulder-fired missiles and adapt it to apply to civilian aircraft. The $122 million program is expected to report its findings early next year.

One source familiar with the department’s work told FOX News that equipping every civilian aircraft is probably not feasible. While the Israelis have a detection system in place, they have far fewer aircraft and airports than the United States does.

FOX News' Kelly Wright and Catherine Herridge contributed to this report.