The NTSB said that after an uncontrolled descent incident involving King Air B200 N777AJ, a test of the oxygen system showed it worked. The crew told the Safety Board they were unable to obtain oxygen after depressurizing the aircraft when they noticed cracking of the windshield. The crew became unconscious and the airplane descended from FL 270 to below 10,000 feet before they recovered and regained control of the aircraft. The airplane sustained wing buckling and other damage.