All Nippon flight 58, a Boeing 727-200, departed Sapporo-Chitose Airport at 13:33 hours local time for a domestic flight to Tokyo-Haneda Airport, Japan. The flight was cleared to follow airway J11L and climb to FL280. About the same time, at 13:28, two North American F-86F fighters of the Japan Air Self Defense Force took off from Matsushima Air Base for a formation training flight. The instructor in one aircraft and a student in the other aircraft (92-7932) were going to practice several formations in training airspace located 9 km from airway J11L. While maneuvering during the formation sequence, the instructor inadvertently flew outside the training airspace. He crossed the airway J11L and then performed a 180 degree turn back towards the training area. In order to do so, the formation had to cross J11L again. The formation was flying about the same altitude as flight 58, causing a conflict. The trainee was following the instructor and did not watch out for traffic when the 727 approached. The instructor ordered him to break away from the 727. The trainee banked to the left but the leading edge of the right wing of his F-86F struck the left horizontal stabilizer of the ANA plane. The fighter’s right wing broke off, causing the plane to crash out of control, but the pilot ejected safely. The Boeing 727 sustained damage to the stabilizer and entered an uncontrolled descent. It passed the sound barrier and subsequently broke up. Cause: The first reason was that the instructor continued the training flight without noticing that he had left the training airspace and entered the jet route J11L. The second reason was: – It is estimated that the All Nippon Airways pilots saw the training aircraft at least 7 seconds before the collision, but the avoidance operation was not performed until just before the collision. This is probably because the ANA pilot did not anticipate the collision. – For the instructor, the trainee’s instruction to avoid a collision was shortly given to the trainee immediately before he saw the ANA aircraft, and he could not avoid the trainee’s collision. This is probably because the instructor was unable to see the ANA aircraft. – About two seconds before the collision, the trainee visually recognized the ANA aircraft slightly to the right of the accident aircraft, and immediately performed an avoidance operation, but was unable to avoid the collision. It is considered that this is because the trainee had little experience in this manoeuvre and was mainly devoted to maintaining the relative position with the instructor aircraft, and it was delayed in observing the ANA aircraft.