Skiers at the Snowbird resort near Mineral Basin were about 100 metres from the landing zone of two Black Hawks — the US military's workhorse troop carrier and cargo helicopter.
Their video footage showed the helicopters' rotors kicking up clouds of snow as they landed. The blades of one aircraft appeared to strike the other.
“The aircraft probably lost sight of the ground,” said Jared Jones, Utah National Guard spokesman.
He said that a more serious incident may have been averted by the helicopters' close proximity. No casualties were reported.
“We can know that there was portions of the video showing the rotor blade that separated from the helicopter and struck the second helicopter. Fortunately, the second aircraft landed quickly.”
Twitter users asked why the helicopters were training so close to a ski resort, despite the risk that an accident could endanger tourists.
Mr Jones said the area was where Black Hawk crews had been training on a regular basis.
“Utah National Guard does a lot of mountainous training, both in the summer and in the wintertime. It's a normal practice for us,” he said.
“This is an LZ [landing zone] we've been to before on many times — it's an approved landing zone, if you will. And they were conducting winter mountain training at the time of the incident.”