(CNN) -- All 56 people onboard a Turkish plane that crashed in southern Turkey early Friday are believed to have been killed, according to the airline's chief executive officer. The cause of the crash is not yet known.
"Search groups have not seen any survivors as of now," said Atlasjet Airlines CEO Tuncay Doganer.
The MacDonnell Douglas 83, which left Istanbul for Isparta at 00.50 a.m. local time (22.50 GMT Thursday), went down in a mountainous region north of the village of Keciborlu, just as it was preparing to land at Isparta, Doganer said.
He added that the pilot had radioed the tower, saying he was starting his descent.
But the flight, which was carrying 49 passengers and seven crew, never arrived at Isparta airport, which is around 315 km (195 miles) southwest of Ankara, disappearing at around 2 a.m. local time.
Doganer said that conditions at the time of the crash were good. "There was no rain or wind," he said. "The weather could not have been better."
He added that the flight's pilots had just returned from training and were extremely experienced. "It is not a point of issue that the pilots were sleepless or restless."
Doganer said that rescue teams had experienced problems in reaching the crash site due to the high ground. Video shows the fuselage of the plane largely intact but broken into at least three pieces, with the tail and cockpit separated from the body of the aircraft. There appeared to be no evidence of a fire.
The Anatolia news agency reported that the site, around seven miles from the airport, is strewn with debris and passengers' personal belongings. The bodies of some passengers are still strapped in their seats.
The agency added that heavy machinery was being used to remove trees and allow easier access to the area.
The governor for Isparta, Semsettin Uzun, said that the site of the crash did not seem to be on the plane's usual route, the agency reported. "It is impossible to understand how the plane landed there."
Families and friends of those on board the plane have headed to airports at Istanbul and Isparta for any updates, according to local media reports, while others have tried to reach the crash site itself.
Doganer said managers from the company will depart for Isparta later today with relatives of those who were onboard the plane.
Atlasjet leased the plane from Worldfocus Airlines, whose pilots were flying it, Doganer said.
Can Ertuna, of CNN affiliate station CNN Turk, said that Atlasjet was a relatively new company and that none of its flights had been involved in such a serious incident before.
In August of this year two hijackers held passengers hostage on an Atlasjet flight before giving themselves up, while in 2005 an Atlasjet plane left the runway due to wintry conditions. There were no reported injuries from either incident. E-mail to a friend