NTSB Probable Cause

FAILURE OF THE PILOT-IN-COMMAND (PIC) TO ASSURE THAT THE AIRCRAFT MAINTAINED A CLIMB PROFILE AFTER TAKEOFF. FACTORS RELATED TO THE ACCIDENT WERE: DARK NIGHT, THE CREW'S LACK OF VISUAL PERCEPTION AT NIGHT, THE PIC'S LACK OF REST (FATIGUE), AND THE COPILOT'S FAILURE TO ATTAIN REMEDIAL ACTION.