Pilots from time to time encounter laser beams (search) that stray into the cockpit on approach to an airport, but a recent rash of such incidents — at least seven since Christmas — has them worried about an organized effort to take down airliners.

Though there have been no reports of accidents caused by lasers, they can temporarily blind and disorient a pilot and could lead to a plane crash.

The FBI (search) is investigating whether the incidents are pranks, accidents or something more sinister.

Federal agents are looking into two incidents in Colorado Springs, Colo., and one each in Cleveland, Washington, Houston, Teterboro, N.J., and Medford, Ore., according to law enforcement and transportation officials, some of whom spoke Thursday only on condition of anonymity.

Scientists discount the possibility that pilots are merely the victims of a popular new Christmas toy or jokesters toying with a $19 laser pointer from an electronics store.

Loren Thompson (search), who teaches military technology at Georgetown University, said a piece of equipment that could do the things the FBI is investigating would be "fairly expensive and fairly sophisticated."

He characterized it as a reasonably powerful visible light laser that can lock onto a fast-moving aircraft. "That's not the sort of thing you pick up at a military surplus store," he said.

Law enforcement officials say they have no evidence of an organized effort to take down planes. 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 lasers used in light shows or to attract the public to an event.

Hundreds of cases of lasers shining into pilots' eyes have been reported over the past decade; in several, the pilots sustained damage to their eyes.

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 Food and Drug Administration, which regulates laser light shows, consults with the Federal Aviation Administration when someone wants to operate 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 acknowledged the possibility that terrorists could use a laser to attack an aircraft — and that it would be hard to detect and to defend against.

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

Rob Sproc, a pilot who serves as vice president of the Airline Pilots Security Alliance, says pilots should have heard about the recent laser incidents from the government, not from the news media. Whether they're a safety hazard or terrorist threat, he said, "we're a little distressed that the information isn't being passed along the way it should be."

"If it takes you down, it's kind of irrelevant what the source is," Sproc 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 feet 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.