A helicopter that crashed while herding wild horses in Theodore Roosevelt National Park clipped a fence before going down, the National Transportation Safety Board says in its initial report on the incident.
The Bell 206 helicopter was herding horses when its left landing skid caught the top of a 10-foot-high wire fence, according to the report released Friday.
"The pilot reported trying to counteract the roll ... but was unsuccessful," investigators said.
The report includes the description of the crash but does not list an official probable cause.
An NTSB spokeswoman said that will come later, in the agency's final report. Those reports often take months.
The pilot, Ted McBride, of El Aero Services of Elko, Nev., and park wildlife biologist Mike Oehler were treated for minor injuries at a Dickinson hospital and released.
The horse roundup was called off.
McBride was certified through the Interior Department to do contract work for the National Park Service. El Aero Services said he had been flying for the company for 35 years and before last month had never crashed.
The NTSB report matches what was reported by people at the scene
of the Oct. 18 roundup aimed at reducing the size of the park's herd to a more manageable level.
Eyewitnesses said the chopper was hovering a few feet off the ground between two fences, trying to herd a group of horses into an inner corral, when a landing skid hit something and pitched the helicopter to the ground.
It came to rest on its left side outside the corral fence.
Parts of its rotors broke off and flew into the corral, but no people or
horses were hurt.
The NTSB report says the chopper's main rotor blades were destroyed, and that both the main transmission deck and tailboom separated from the fuselage.
The tailboom is the part of the helicopter behind the cabin.
The transmission deck, which helps transmit the force of the engine to the rotors, is on top of the cabin.
Two federal Interior Department investigators were sent from Boise, Idaho, to the park to examine what happened and forward the information to the NTSB.
Stephen Rauch, an air safety investigator with the Aviation Management Directorate, said his agency leaves the probable cause determination to the NTSB and focuses on National Park Service issues.
"Are we doing things the right way, at the right time, with the right equipment?" he said, offering examples of the kinds of things that he will include in his final report, which also likely is months away.
Park Superintendent Valerie Naylor has said the park likely will continue using helicopters because they are the most efficient and safest way to round up wildlife.
Helicopters have been used in park roundups for about 20 years.