Regulators are concerned that a collision between a drone and a plane, which could easily occur at a speed of 200 miles (320 kilometers) an hour or more, may damage an aircraft or its engines. Encounters with drones can also cause pilots to be distracted from other critical tasks.

Industry groups estimate that as many as 500,000 drones have been sold in the U.S., many of which are capable of flying thousands of feet above the ground.

Fighting fires

In recent weeks, drones have been spotted by airline pilots near airports in Newark, New Jersey, New York and Minneapolis, according to the FAA. Last month, there were about a dozen cases of drones flying near aircraft attempting to fight wildfires in California, forcing groundings and delays in battling the blazes, said Lynnette Round, a spokeswoman for Cal Fire, as the California Department of Forestry and Fire Protection is known.

In July, pilots reported 137 incidents compared with 36 for the same month in 2014. There were 138 such cases in June.

Tim Canoll, president of the Air Line Pilots Association, urged the public to help stem the growing threat. “If you are near an airport and you see someone lifting one of these things off, you should call 911,” Canoll, head of the largest pilots’ union in North America, said.

ALPA supports additional regulations on small drones that require registering the devices and installing automatic software blocking flights into prohibited areas, Canoll said.

Senator Dianne Feinstein, a California Democrat, has sponsored legislation requiring tougher requirements on drones sold to hobbyists.

Five cases

FAA enforcement cases against drone operators so far haven’t kept pace with incidents. The agency has settled only five civil cases involving unmanned flights that violated regulations, according to FAA data. One involved a Swiss citizen who flew over the University of Virginia campus filming a promotional video.

Cracking down on rogue drone operators is a priority, the agency said. “The FAA also is working closely with the law enforcement community to identify and investigate unauthorized unmanned aircraft operations,” the agency said in the release. It has opened “dozens” of enforcement cases.

The increase in incidents comes in spite of an effort by the FAA and the drone industry to educate users about safety. The group, called Know Before You Fly, has a website with guidance on how to operate drones.

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