Mount Osutaka is a mountain in Ueno, Gunma Prefecture, Japan. It is 1,639 m high. The plane crash of Japan Air Lines Flight 123 on 12 August 1985 was initially reported on Mount Osutaka, but later confirmed to be on a ridge near Mount Takamagahara. With the loss of 520 people, it remains the deadliest single-plane accident in world history.