What happened
On May 2, 2019, a Glaser-Dirleks DG-500 Elan Orion glider, registered JA505G, was conducting a leisure flight near Hida Air Park in Gifu Prefecture. The flight, operated by the Central Japan Aeronautic Association, Gifu Division, was intended to showcase mountain scenery to a passenger. While navigating the ridge near Mt. Jukkoku, the pilot attempted to maintain altitude by flying close to the mountain slope to utilize ridge lift.
During the maneuver, the pilot became preoccupied with maintaining distance from the slope and failed to monitor the aircraft's heading using available instruments. This lack of situational awareness led the glider to deviate from its intended course toward Mt. Yakedake, instead turning southeast. The aircraft crossed the ridge of Mt. Norikura, entering the lee side where it encountered strong downdrafts.
As the aircraft rapidly lost altitude, the pilot attempted to turn back, but the glider had already descended into a zone of significant sinking air. Realizing that the ground was approaching too quickly and finding no suitable open landing area, the pilot executed a forced landing into a forested slope. The impact with trees resulted in the destruction of the aircraft, specifically breaking the fuselage and the right wing, though there were no injuries to the occupants.
The investigation
The Japan Transport Safety Board (JTSB) examined the flight path using GPS records and pilot statements. The investigation focused on the meteorological conditions, specifically the presence of ridge-induced updrafts and downdrafts, and the pilot's use of navigational instruments. Investigators also reviewed the pilot's familiarity with the specific terrain and the club's established flight procedures regarding alternate landing sites.
Findings
- The pilot's concentration on maintaining distance from the mountain slope caused him to lose sight of the primary visual target, Mt. Yakedake.
- The pilot failed to use the magnetic compass or the GPS navigation system to verify the aircraft's heading and position.
- Due to a lack of prior experience flying north of Mt. Jukkoku, the pilot could not accurately identify his position through landscape recognition alone.
- The pilot mistakenly believed the encountered downdraft was a localized effect from a valley pass rather than the lee-side sink of the Mt. Norimura ridge.
- The pilot lost his position and wandered into the downdraft zone because he lacked sufficient terrain knowledge and was not utilizing navigational instruments.
- The aircraft's altitude was insufficient to safely navigate the lee side of the ridge given the strength of the downdrafts.