Updated

The FBI, concerned that terrorists could use lasers as weapons, is investigating why laser beams (search) were directed into the cockpits of seven airplanes in flight since Christmas.

Laser beams can temporarily blind or disorient pilots and possibly cause a plane to crash.

The FBI is looking into two incidents in Colorado Springs, Colo., and one each in Cleveland, Washington, Houston, Teterboro, N.J., and Medford, Ore., according to federal and local law enforcement and transportation officials, some of whom spoke only on condition of anonymity.

A federal law enforcement official, who declined to be identified by name, said Thursday there is no evidence of a plot or terrorist activity. But pilots are troubled by the incidents, and the FBI (search) earlier this month warned of the possibility that terrorists might use the devices as weapons.

"It's not some kid," said Paul Rancatore, a pilot who serves as deputy chairman of the security committee for the Allied Pilots Association (search). "It's too organized."

Loren Thompson, who teaches military technology at Georgetown University, called it a "rather worrisome development," though he said experts would be more puzzled than alarmed.

"What we're talking about is a fairly powerful visible light laser that has the ability to lock onto a fast-moving aircraft," Thompson said. "That's not the sort of thing you pick up at a military surplus store."

Thompson said a piece of equipment that could do the things the FBI suspects would be "fairly expensive and fairly sophisticated."

"It sounds like an organized effort to cause airline accidents," Thompson said.

Law enforcement officials, though, say they have no evidence of such an effort and that the lasers in question are readily available. Further, they say they've had reports of similar incidents since the technology became popular.

But a memo sent to law enforcement agencies recently by the FBI and the Homeland Security Department says there is evidence that terrorists have explored using lasers as weapons, though there's no intelligence that indicates they might use them in the United States.

Pilots and safety officials have long been concerned about the dangers of laser light shows, which have caused temporary eye injuries to several pilots over the last decade.

Most recently, a pilot for Delta Air Lines reported an eye injury from a laser beamed into the cockpit while approaching the Salt Lake City airport in September. The plane landed safely.

The Civil Aerospace Medical Institute has a database of several hundred reports in which civilian or military aircraft were illuminated by lasers. Though there have been no accidents reported, pilots in some cases were startled, temporarily blinded and disoriented.

The Food and Drug Administration, which regulates laser light shows, consults with the FAA when someone proposes operating a laser outdoors near an airport. The FAA recommends the maximum safe level of laser light exposure for pilots maneuvering near airports.

An FAA-commissioned study released in June concluded that "a laser attack could be quickly deployed and withdrawn, leaving no obvious collateral damage or projectile residue, and would be difficult to detect and defend against."

"A sufficiently powerful laser could cause permanent ocular damage, blinding crewmembers and make a successful landing virtually impossible," the report said.

More recently, some pilots have pushed to analyze the possible dangers posed by terrorists trying to cause an accident with the devices.

"It's a low-tech way to cause crashes," Rancatore said.

On Christmas night, two SkyWest pilots said they saw two laser-like rays of light in their cockpit as they attempted to land at the airport in Medford, Ore., according to FBI spokeswoman Beth Anne Steele.

On Monday, a laser beam was directed into the cockpit of a commercial jet flying about 15 miles from Cleveland Hopkins International Airport at an altitude of between 8,500 and 10,000 feet, FBI special agent Robert Hawk said. It was determined the laser came from a residential area in suburban Warrensville Heights.

Also on Monday in Colorado Springs, two pilots reported green pulsating laser lights beamed into their cockpits. Police sent patrol cars and a helicopter in a fruitless search. FBI spokeswoman Monique Kelso said the bureau is continuing to investigate.

In New Jersey, the pilot of a corporate-owned Cessna Citation carrying 13 people said three green lasers were pointed into his cockpit while approaching the Teterboro airport on Wednesday night. Law enforcement officials said they were believed to have originated near a mall in Wayne, according to Passaic County Sheriff's Office spokesman Bill Maer.

All the planes landed safely.