All Nippon Airways crash off Shimoda

The All Nippon Airways crash off Shimoda (Zen Nikkū Shimoda-oki tsuiraku jiko) was an aviation accident in which All Nippon Airways Flight 25 crashed off Shimoda, Shizuoka Prefecture, Japan, on 12 August 1958. It was the first fatal accident to occur since the founding of the Japanese airline All Nippon Airways, and in the end the cause of the accident could not be determined.

Overview of the accident

At around 8:30 pm on 12 August 1958 (Shōwa 33), a Douglas DC-3 twin-engine piston airliner operating as All Nippon Airways Flight 25 from Haneda Airport, Tokyo, to Nagoya Airfield (Komaki Airport) (registration JA5045; 30 passengers and 3 crew, a total of 33; departed Haneda at 7:53 pm), while flying over the sea off Shimoda City on the Izu Peninsula, informed its sister aircraft Flight 16, operating nearby from Osaka to Tokyo, that "the left engine has malfunctioned and stopped" and "we are now returning to Haneda Airport"; after that, with a communication at 8:55 pm as its last, it lost contact and Flight 25 went missing.

From early on the following morning, the 13th, after contact was lost, a large-scale search was begun to find the missing aircraft, with Japan Coast Guard patrol vessels and Self-Defense Force aircraft also cooperating. However, on that day strong winds were raging at sea and the waves were high, so the search was difficult and the aircraft could not easily be found.

At around 0:30 pm, the crash of Flight 25 was confirmed in the sea near Toshima island, 17 km, off Shimoda on Izu, and all 33 crew and passengers were killed. As a result of the search, which continued in conditions made rough by strong winds and high waves, passengers' luggage as well as seats, a toilet door, parts of the airframe and other wreckage destroyed by the impact of hitting the sea surface were found, and the bodies of 18 victims were identified and recovered. In the end the remaining 15 victims and most of the airframe could not be found or recovered, and the search was called off.

It was later confirmed that the airframe of Flight 25, which had crashed into the sea, had sunk to the seabed at a depth of 600 m. In 1958 there was neither the technology nor the associated equipment to raise an airframe to the surface, so the crashed aircraft could not be raised.

Cause of the accident

At the time aircraft were not fitted with flight data recorders, cockpit voice recorders and the like, and the ultimate cause of the accident could not be identified. In addition, since the toilet door recovered from near the crash site was found in a locked state, the possibility was also pointed out that a passenger had been using the toilet until just before the accident. It is therefore presumed that the aircraft crashed into the sea within a short time of the trouble with the aircraft arising.

As for the trouble thought to have caused the accident, in addition to the engine malfunction, a malfunction of the manual gyrocompass has also been cited. Among the eyewitness accounts from the ground was one that "the remaining right engine was also on fire". With reference to that testimony, there was also speculation that many troubles occurred on the aircraft, leading to the crash. The accident investigation report submitted to the Minister of Transport on 2 September also pointed out these possibilities, and concluded that it was difficult to identify the cause.

Among the theories put forward later is one that, along with the engine malfunction, the vacuum pump for the artificial horizon malfunctioned, the pilot failed to switch pumps so that it stopped working, and the aircraft was flying blind and crashed into the sea at night. At the time All Nippon Airways was short of funds, and moreover the DC-3 aircraft it owned had been collected as second-hand airframes from various American airlines, so there was also the problem that their specifications were not standardised.

For that reason the cockpit instrument panels and switch layouts also differed from aircraft to aircraft, and it is a fact that pilots were confused in handling them. Moreover, of the 9 DC-3 aircraft then in service, only this aircraft, the one that crashed, required the vacuum pump driving the artificial horizon to be switched over with a switch if either the left or right engine stopped working. For that reason the theory was also advanced that the pilot did not know where the changeover switch was and mistakenly disabled the artificial horizon. However, since salvage of the cockpit section was never actually carried out, its truth remains unknown.

Impact of the accident

As countermeasures to the accident, All Nippon Airways first received 12 mechanics seconded from Itochu Aviation Maintenance and 5 engineers from Japan Airlines and JAL Maintenance. In addition, to have spare maintenance capacity, it reduced operating hours from 2900 hours a month at the time of the accident to 1800 hours. Furthermore, All Nippon Airways obtained a subsidy of 50,000,000 yen from the government, modified and overhauled the control systems of all the DC-3 aircraft it owned, and standardised their specifications.