 The subsequent investigation by the National Transportation Safety Board concluded that the cause of the accident was the captain's premature descent below the minimum descent altitude, carried out without having the runway in sight.The accident's investigation also brought into focus several generic safety issues, such as pressure applied on charter pilots by customers, night flight into airports near mountainous terrain, and the ambiguity of some Federal Aviation Administration rules.The captain and first officer reported for work at Avjet's Burbank, California facility around noon on the day of the accident.