Accident Overview
On Saturday, May 25, 2024, at approximately 16:22 Japan Standard Time, a glider registered as JA2189 (Alexander Schleicher ASK13) crashed after releasing from an aerotow and attempting a forced landing in Ubuyama Village, Aso County, Kumamoto Prefecture. The glider was operated by the Kyushu Institute of Technology and was being flown solo by a 20-year-old student pilot holding a private glider certificate. The tow aircraft was an Avions Pierre Robin DR400/180R (registration JA4319) operated by Makurazaki Glider Club.
Flight History
The glider departed Runway 08 of the Aso Temporary Operation Site at 16:14 for a training flight. Prior to departure, the manager of the Kyushu Institute of Technology Gliding Club instructed the tow pilot to follow a 24 km flight course and release the glider near Ohso Dam at an altitude as high as possible, such as 700 m AGL. The tow pilot planned to climb to 6,000 ft (about 1,000 m AGL) based on the TCA floor. This was the glider pilot's first solo aerotow flight.
During the tow, speed gradually increased. Passing the Minami Cattle Feedlot, the speed reached 140 km/h, the aerotow speed limit for the glider, and continued to rise. At the first turn point, about 11 km from departure, the speed reached 150 km/h. The tow plane executed a 90° right turn. The glider pilot, feeling alarmed, opened dive brakes to reduce speed, but the climb rate decreased and speed increased further. The glider pilot radioed the tow pilot, who acknowledged the high speed (about 150 km/h) and pulled back on the control stick to increase pitch. However, the glider accelerated to 170 km/h, causing severe slack in the towline. The glider pilot released the towline to prevent entanglement.
After release, the glider pilot stabilized the aircraft and checked the altimeter, which indicated 320 m (set to 0 m at takeoff). Being more than 10 km from the departure site, the pilot determined it was impossible to return. Spotting a grassland, the pilot initiated a forced landing approach—the first forced landing attempt for the pilot.
Forced Landing Attempt
On final approach, the pilot noticed the field had a slope (later determined to be approximately 6° downslope). The pilot opened dive brakes and attempted to land, but overshot. The glider's wing struck a tree at the end of the field, then the glider flew over a parking area, hit more trees, and came to a stop after turning left 90°.
Damages and Injuries
The glider sustained damage: the right wingtip, the left wing broken in the middle, the nose buckled, and the right horizontal stabilizer broken. The glider pilot was examined at a hospital and found to have only minor injuries such as scratches.
Meteorological Information
At the time of the accident, observations at the Takeda Regional Meteorological Observatory Station (about 20 km east-southeast of the site) reported wind from east-northeast at 2.5 m/s and a temperature of 25.0°C.
JTSB Analysis
The Japan Transport Safety Board (JTSB) analyzed the accident and concluded:
- The tow pilot towed the glider at an altitude well below that required for a safe return to the departure site in an emergency. The glider was towed on a flight path that left it without sufficient altitude to glide back (based on an operational glide ratio of 15). The tow pilot focused on reaching the planned release altitude at Ohso Dam and did not consider the required altitude for the glider to return.
- The towing speed exceeded the glider's aerotow limit of 140 km/h. The climb rate became negative after reaching that speed. The tow pilot, unaware of the glider's speed limit, likely reduced pitch unconsciously, increasing speed and decreasing climb rate. The tow plane's tight right turn made it difficult for the glider to follow, causing the glider to pitch down and exceed the speed limit, leading to significant slack in the towline.
- The glider pilot should have confirmed aerotow speed limits with the tow pilot during pre-flight briefing and should have contacted the tow pilot by radio earlier to correct the high speed.
- The forced landing field had a downslope of about 6°, which contributed to the pilot's inability to land within the field.
Probable Cause
Not specified in the report.
Aircraft Information
Glider: Alexander Schleicher ASK13, serial number 13526, manufactured December 9, 1975. Airworthiness certificate valid until February 22, 2025.
Tow plane: Avions Pierre Robin DR400/180R, serial number 1236, manufactured September 22, 1977. Airworthiness certificate valid until September 14, 2024.
Personnel Information
Glider pilot: Age 20, private pilot certificate (glider) issued January 23, 2024, with competency valid until January 23, 2026. Class 2 medical certificate valid until March 24, 2029. Total flight time: 27 hours 20 minutes, with 2 hours 15 minutes in the last 30 days.
Tow pilot: Age 71, private pilot certificate (land single-piston) issued September 5, 1973, with competency valid until October 11, 2024. Class 2 medical certificate valid until November 11, 2024. Total flight time: 853 hours 35 minutes, with 3 hours 15 minutes in the last 30 days.