A pilot and two co-pilots, all three of them Libyan, were killed Sunday when their cargo plane crashed in southern Libya, a military source said.The plane crashed minutes after taking off from the Al-Sharara oil field, the source said on condition of anonymity."It had arrived from Tripoli to bring supplies to the (oil) field staff and left empty," the source told AFP."The captain and his two co-pilots died in the crash of the C-130 aircraft."One member of the crew survived the wreck but was "seriously injured", the source said.In a statement shortly after the crash, Libya's National Oil Company said the plane crashed two kilometres away from the field "after delivering 18 tonnes of catering and maintenance supplies".The NOC said the aircraft belonged to the Libyan Air Force. Akakus Oil, which runs the Al-Sharara field, had chartered the plane because local access roads have been closed due to security issues in the area.The cause of the crash at Al-Sharara, one of Libya's biggest oil fields in the south of the country, was unknown.