More questions than answers on counter missile technology.

The Department of Homeland Security, which was tasked by Congress to study options to protect commercial airliners from shoulder-fired missiles, sent a relentlessly downbeat report to Capitol Hill, detailing just how many hurdles it must overcome to outfit every jetliner with protective devices.

On the technological side, results of preliminary tests show a laser-based system "partially meeting the DHS performance requirements." But these tests are being carried out on the Boeing 767 and McDonnell Douglas MD-11, which comprise only 5 percent of the domestic commercial fleet. Federal Aviation Administration certification for the technology will have to be approved separately for each aircraft type. There is still much work to be done on the narrow-body, regional jets that the commuter airlines use. Most shoulder-fired missiles are designed to take down smaller aircraft such as these.

Logistically, there are still few answers on the maintenance burden for airlines. However, inflation and fuel are now expected to cost the airline $365 per flight, up from $300 at the beginning of the project. During Phase Ill of the development process, counter-missile technology will be installed on courier jets to give engineers real-world data.

"Until a significant number of [counter-missile] units are installed and maintained by airlines, uncertainty regarding operation and maintenance costs will remain," the report said.

On the bureaucratic and legal side, complications may arise when flying aircraft overseas. The military-based technology will run afoul of International Traffic in Arms Regulations that prohibit the export of such systems. Furthermore, each country where the airplane lands would have the right to certify the system's safety. Airlines have expressed fears that they would be held liable in the event that a missile penetrates the protective shield and takes down an aircraft.

DHS estimated it would take 20 years to equip every U.S. airliner with missile defenses.

Meanwhile, the Center for Risk and Economic Analysis of Terrorism Events at the University of Southern California said coordinated shoulder-fired missile attacks on multiple airliners would cost the U.S. economy about $250 billion.

"We believe that could have the same effect as 9/11 on the airline industry with the ripple effects on the economy," said Detlof von Winterfeldt, the co-author of a report on the cost effectiveness of missile countermeasures.

The model doesn't assume that every missile fired would successfully take down an airliner. Even if the terrorists missed, "at that point, the public, the newspapers will know that there is this capability, and I think there will be a significant impact on the airline industry," he told National Defense.

The report's aim was not to specifically endorse counter-missile programs, but to outline the possible impact of such attacks. The best that it can do is say "that this is seriously worth considering," he added.