Accident Overview
On April 9, 2023, at about 13:19 JST, a privately owned PZL-Bielsko SZD-55-1 glider (registration JA2502) crashed into the bank slope of Yamba-Agatsuma Lake in Yokokabe, Naganohara Town, Agatsuma County, Gunma Prefecture. The pilot, the sole occupant, was fatally injured. The glider was destroyed, but there was no fire.
Flight History
The glider took off from Nagano City gliding field (elevation 338 m) in Nagano Prefecture at about 12:00 via winch launch for training. The pilot had attended a pre-flight briefing at about 09:30 where the instructor advised caution due to forecasts of strong northwesterly winds and mountain waves. At about 12:30, the pilot reported climbing well at 2,600 m near Mt. Neko. At about 12:44, the pilot inquired about conditions near Mt. Azumaya. The glider crossed the prefectural boundary into Gunma Prefecture at about 12:56. At about 13:19, it crashed into the bank slope at elevation 572 m.
Injuries and Damage
The pilot sustained fatal injuries. The glider was destroyed, with the cockpit destroyed, right wing root cracked and deformed, and fuselage tail broken.
Personnel Information
The pilot was 68 years old, held a private pilot certificate for high class gliders (issued June 4, 1975), with a total flight time of 641 hours 06 minutes, including 64 hours 31 minutes on the glider type. The pilot's last 30-day flight time was 2 hours 51 minutes.
Glider Information
The glider was a PZL-Bielsko SZD-55-1, serial number 551192033, manufactured March 10, 1992. It had a valid certificate of airworthiness (No. 2021-57-20, valid until December 24, 2023). At the time of the accident, weight and center of gravity were within allowable limits.
Meteorological Conditions
At 12:00 on April 9, 2023, a high-pressure system covered the main island of Japan with a pressure gradient between a high moving east from the continent and a low near the Kuril Islands. A Significant Weather Analysis Chart at 09:00 indicated mountain waves (FL 20-180, weakening) in the Kanto Plain; the chart at 12:00 showed none. A Narrow Area Significant Weather Prognostic Chart at 09:00 predicted moderate turbulence (FL 40-90) near the Nagano-Gunma border; the chart at 13:00 predicted none. Observations at the ridge near the prefectural border at about 13:30 recorded wind from 300°-310° at about 62-65 km/h (17-18 m/s). At Nagano City gliding field at 12:00, wind was 040° at 6-8 m/s, weather fine. At Yamba Dam Branch Office (4 km northeast of accident site) at 13:20, wind was west, instantaneous wind velocity 5.7 m/s, maximum gust 10.2 m/s, temperature 10.6°C.
Additional Information
At the time of the accident, four other gliders from the same association were flying in the area, with three performing ridge soaring and one wave soaring. Strong northwesterly winds (17-18 m/s) produced strong updrafts and downdrafts that changed within a few hundred meters. No clouds were present. Ridge soaring uses updrafts created by wind hitting upwind slopes; downdrafts on the lee side can be strong. The FAA Handbook advises making all turns away from the ridge to avoid descending into the lee side.