According to a survey, jointly conducted by All Nippon Airways and Japan Air Commuter, 49 of the 52 DHC-8-400 incidents were the result of design and production flaws. Of the 52 cases, 19 were caused by failures involving landing gear. Flight control system malfunctions, such as the autopilot system and steering failures, accounted for 11 cases. Engine problems were cited five times. Door problems also occurred five times. Four cases were related to hydraulic pressure systems, two were related to electrical equipment to maintain in-flight cabin pressure, and the remaining six were caused by other reasons.
Concerning their causes, landing gear problems happened five times due to air accidentally entering hydraulic pumps, affecting normal operations. The remaining cases were caused by electrical failures in wiring and other errors. Flight control system malfunctions were mainly caused by failures in flight control computers and improper repairs of sensors on elevator control systems. The two airlines suspect that most of the cases were failures as a result of the introduction of the new type of aircraft and said they had had some parts changed or improved. (The Yomiuri Shimbun.)