PHOENIX -- A medical helicopter crashed in rugged terrain east of Phoenix, killing two crew members and seriously injuring a third, who was still able to use a flashlight to signal search aircraft, a sheriff said Wednesday.

Pinal County Sheriff Paul Babeu said the medical helicopter crashed Tuesday evening on a cliff or mountainside about 12 miles north of Superior, a mining community outside Phoenix.

Air Methods, which owns the company operating the aircraft, said the chopper was carrying a pilot, a paramedic and a nurse. No names were released.

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Air Methods spokeswoman Christina D. Brodsly said in an email that no patients were on board. Babeu said the helicopter was flying from a Mesa airport east to Globe, but he said he didn't have any more information on the purpose of the flight.

"We are deeply saddened by the news that two of our crew members were taken from us, and our hearts go out to their family and loved ones," Brodsly said in a statement, according to CBS affiliate KPHO-TV.

Babeu said an aerial search began after the helicopter was reported missing around 6 p.m. and that he knew of no radio transmission from the aircraft before it went down or any report from the public about a crash in the Tonto National Forest.

A military aircraft rescued the survivor at about 10:15 p.m., and that person was taken to a trauma center in the Phoenix area in "very serious, critical condition," Babeu said.

A Native Air helicopter first spotted the wreckage at about 8:30 p.m. and an Arizona Department of Public Safety helicopter located it about a half-hour later, but neither was able to land because of rugged terrain.

"From what I understand it's in a precarious situation," he said of the crashed helicopter.

The DPS helicopter crew saw the survivor signaling with a flashlight, Babeu said.

The crash scene was sealed off overnight to preserve evidence before National Transportation Board Safety investigators arrive later Wednesday, Babeu said.