PHOENIX -- A tour helicopter carrying seven people on board crashed in the Grand Canyon, killing three people and injuring four others.

Six passengers and a pilot were on board the Papillon Grand Canyon Helicopters chopper when it crashed around 5:20 p.m. Saturday on the Hualapai Nation near Quartermaster Canyon, Hualapai Nation Police Chief Francis Bradley said, according to CBS affiliate KPHO-TV. The four who were injured were level 1 trauma patients and were being treated at the scene.

An after-hours phone call and email to Papillion were not immediately returned Saturday. The company's website says it flies roughly 600,000 passengers a year on Grand Canyon and other tours. It also notes that it "abides by flight safety rules and regulations that substantially exceed the regulations required by the Federal Aviation Administration."

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Longtime helicopter crash lawyer Gary C. Robb represented a woman badly burned in a deadly Papillion crash at the Grand Canyon in 2001. He said the company has made big improvements since that crash.

"They've improved their piloting qualifications as well as their maintenance over the last 10 years and as far as I know they've not had a crash since 2001," he said. He said flying in the Grand Canyon can be treacherous simply because of the number of helicopters there.

Federal Aviation Administration spokesman Allen Kenitzer said the Eurocopter EC130 crashed in unknown circumstances and sustained heavy damage.

Robb said his heart went out to the victims.

"This is not just the fact that a helicopter crashed, this is a human tragedy. People died and were horribly injured. It's a tragedy for human beings," Robb said.