(NECN) - Federal investigators will be on the scene of a deadly helicopter crash in Arizona on Monday.
Six people were killed and another was critically injured when two choppers collided near Flagstaff Medical Center.
At least one of those helicopters was approaching the hospital at the time.
An official with one of the helicopter companies says Flagstaff Medical Center doesn't have flight controllers.
That means pilots need to watch each other and communicate their locations by radio.
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