Scheduled Revenue Flight

An undetected electrical short within the left nickel-cadmium aircraft battery, which resulted in the absorption or an increasing amount of heat energy over an unknown period of time and progressed to a state of thermal runaway.

It was determined that the military pilot under training failed to see and avoid other traffic while conducting a training mission. Relatively inexperienced, the trainee pilot had a total of 25 flying hours and delayed a corrective manoeuvre as ordered by his instructor. This caused the right wing of the Sabre to struck the horizontal stabilizer of the B727.
The following factors were identified:
- The instructor continued the training flight without noticing that he had left the training airspace and entered the jet route J11L.
- 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.

Wrong approach configuration.

One of the flight data recorder was out of service at the time of the accident due to lack of sufficient technical controls. The second data recorder disconnected when the right main gear impacted the runway surface. Investigations revealed that the aircraft' speed was 32 km/h lower than the prescribed speed when the vertical speed was too high, which prevented the pilots to complete a correct touchdown and avoid the violent impact with the runway surface. Aerodynamic forces recorded at impact exceeded the certification of the aircraft, resulting in a loss of control and then the failure of the left wing. The probable cause of the loss of speed on short final could be the combination of a series of erroneous actions on part of the flying crew, coupled with incorrect speed indication, possibly be due to a leak of the power system that occurred at low altitude and in marginal weather conditions.

The flight crew mistook a point approximately 5 nautical miles north of the Hakodate NDB as being just over the Hakodate NDB, a navigation aid, and initiated their descent from an estimated altitude of 6,000 feet in an attempt to cross the high station at 2,500 feet by making a single circle. The outbound flight leg was extended westward and because of a strong southwesterly wind, the aircraft drifted further to the north than the crew expected, striking the mountain. It is so considered that the accident was the consequence of a controlled flight into terrain.

Double engine failure in flight for undetermined reason.