YESILYURT, Turkey - An Atlasjet plane crashed on a rocky mountain shortly before it was due to land in southwest Turkey early Friday, killing all 56 people on board. The cause was not immediately known.

The MD-83, carrying 49 passengers and seven crew members, took off from Istanbul around 1 a.m. local time headed to Isparta on a flight of about one hour, but went off the radar just before landing at the airport.

At about 7 a.m., a rescue helicopter reached the plane's wreckage near the village of Yesilyurt, in Isparta province, and reported that no one had survived the crash, said Tuncay Doganer, the airline's chief executive. Doganer said the cause of the crash was unknown, but ruled out technical failure and said the weather and visibility were good. "The pilot saw the airport and informed the tower that it was inbound. The plane then disappeared," he said. Investigators found the flight data and cockpit voice recorders, which will help them determine the cause of the crash, the civil aviation authority said.

In a statement, Atlasjet said the wreckage of the plane was found on a mountain around 5,000 feet high, and that rescuers initially had difficulty reaching the site because of the rugged terrain. The area where the plane crashed is called Turbe Tepe, which means "Shrine Peak" in Turkish. Much of the wreckage lay amid snow patches 650 feet from the top of the mountain.