Despite a ban on drones in the National Park System, people continue to fly them and, in some cases, endanger working aircraft/NPS

Drones can offer incredible vantage points for photographers, but they also can be a danger to aircraft. And so when a drone appeared in the air near Glen Aulin in Yosemite National Park, a park helicopter had to land rather than risk collision.

The helicopter was transporting materials one day last week but had to land because the drone "was flying too close to the helicopter," said park spokeswoman Jamie Richards. 

"We have no information on if the drone pilot was located and any actions that were taken. The incident was reported and the helicopter mission had to be postponed," she said Thursday.

Unauthorized flying of drones in national parks was outlawed in 2014 by the National Park Service over concerns that they can stress wildlife, bother visitors, and interfere with official aircraft.

The ban was announced after several incidents in the park system:

* In April 2014, a drone at Grand Canyon National Park buzzed around more than three dozen visitors gathered to watch a sunset near Desert View Watchtower. "The operator lost control of the unmanned aircraft, which had been loudly flying back and forth over the canyon, and the device crashed into the canyon," Park Service records noted

* In May 2014, officials at Yosemite warned visitors that flying drones in the park was illegal, and a few days later Zion National Park officials said someone had been buzzing bighorn sheep with a drone.

* In the fallof 2013, according to the Park Service, a drone was confiscated at Mount Rushmore National Memorial in South Dakota after it flew above a crowd of more than 1,000 and in front of the sculpted profiles of presidents Theodore Roosevelt, George Washington, Thomas Jefferson, and Abraham Lincoln.

There have been several drone-related incidents in Yellowstone National Park, including a drone that crashed and sank in Grand Prismatic Spring in August 2014. The National Mall in Washington, D.C., also has seen dozens of drone incidents.