What happened
On October 26, 2010, a Boeing 737-800, registration JA55AN, was performing a scheduled flight from Chubu Centrair International Airport to Asahikawa Airport. While descending toward its destination under the direction of Sapporo Air Traffic Control, the aircraft encountered a series of terrain alerts.
As the aircraft descended through approximately 7,200 ft, the crew requested a right turn to return to the Asahikawa VOR. Shortly after initiating this turn, the Enhanced Ground Proximity Warning System (EGPWS) issued a "CAUTION TERRAIN" alert. This was quickly followed by "TERRAIN" and "PULL UP" warnings as the aircraft's altitude dropped toward 3,200 ft.
In response to the warnings, the flight crew disengaged the autopilot and auto-throttle, applying significant nose-up input and increasing engine power. The aircraft performed an emergency climb to avoid the terrain, passing near the peak of Mt. Pippu. During the maneuver, the aircraft's radio altitude reached a minimum of approximately 713 ft. After the immediate danger passed, the crew notified air traffic control that they had cleared the terrain area and requested continued radar vectors. The flight eventually landed safely at Asahikawa Airport at 14:05 JST with no injuries to the 51 passengers or 6 crewmembers on board.
The investigation
The Japan Transport Safety Board (JTSB) examined the flight records from the Digital Flight Data Recorder (DFDR) and Cockpit Voice Recorder (CVR), as well as communications with Sapporo Air Traffic Control. The investigation focused on the descent profile, the instructions provided by the controller, and the crew's decision-making during the descent. Investigators also reviewed the aircraft's EGPWS performance and the flight crew's adherence to minimum vectoring altitudes (MVA) in the area.