Event
On 20 June 1998, at approximately 16:20 local time, a LAK-12 "Lietuva" glider (registration LY-GDH) belonging to the Kaunas County Aviation Sports Club was involved in an accident at Pociūnai Aerodrome. The glider was piloted by a 43-year-old club member who held a glider pilot license valid until 28 May 1998, with 1,700 total flight hours including 1,200 hours on the LAK-12 type. The flight task was soaring in the aerodrome area under good meteorological conditions.
For takeoff, the pilot selected an unmown section of the grass aerodrome. During the initial ground roll behind a W-35 "Wilga" towplane, the glider accelerated with a slight right bank, its wing contacting the grass. As the takeoff run progressed, the increasing resistance from the grass and the right bank led to an uncontrolled flat spin about the vertical axis. Both the glider and towplane pilots released the tow rope almost simultaneously. The glider then rose to approximately 2 meters and struck the ground uncontrollably.
Consequences
No persons were injured in the accident. Examination of the glider revealed the following damage: a broken wheel lever, a cracked fuselage in two locations, stabilizer damage near the end ribs, and a broken canopy mounting bracket. The glider was deemed repairable only under factory conditions. No damage was caused to third parties.
Meteorological Information
Weather observations from Kaunas aerodrome, the nearest station, recorded at 14:50: wind 320° at 10 knots, visibility more than 10 km, 5-7 octas of cloud at 4000 ft with cumulonimbus, temperature 17°C, QNH 1015 hPa. At 15:50: wind 270° at 10 knots, visibility more than 10 km, 5-7 octas at 5000 ft with cumulonimbus, temperature 18°C, QNH 1015 hPa. The forecast for the sector from 14:00 to 21:00 indicated wind and temperature at 300-1500 ft layer 360° 16 KT/12°C, surface wind 340° 10 gusting 20 KT/19°C, visibility 10 km with local 3000 m, rain showers, thunderstorms, cloud 5-7 octas stratocumulus at 2000 ft and cumulonimbus at 2500 ft.
Aerodrome Information
Pociūnai Aerodrome is a grass airfield with sufficient area for safe takeoffs in any direction using a tow vehicle. Runway markings were absent. A portion of the aerodrome was unmown. In the area selected for takeoff, grass height ranged from 0.2 to 0.3 m, with local areas up to 0.5 m.
Communication and Equipment
Radio communication between the glider, towplane pilot, and flight director was reported to be without issues. A barograph installed in the glider was activated during the flight but, due to the short duration and its limited capabilities, only recorded the time of the accident.
Wreckage and Impact Characteristics
Examination of the wing marks in the grass indicated that during the initial acceleration, the glider had a slight right bank and the wing occasionally contacted the grass. The bank was not corrected during the further run, as evidenced by subsequent wing marks. At an estimated speed of 60 km/h (stall speed), approximately 80 to 100 meters from the start of the takeoff roll, the right wing encountered taller grass, leading to increased resistance and initiating the uncontrolled flat spin. Immediately afterward, both pilots released the tow rope. The abrupt stoppage of the right wing caused the left wing speed to increase, and the glider rose to about 2 meters before striking the ground nose-first at a shallow angle, followed by the landing gear wheel and tail skid. The impact caused structural deformation and broke the landing gear wheel together with its support.
Safety Factors
The pilot's seat and safety harness functioned fully, and the pilot was not injured.
Analysis
The investigation analysis noted that during the takeoff roll, the glider accelerated with a right bank while the wing contacted the grass. At an estimated speed of 60 km/h and after about 80-100 m, the right wing entered grass up to 0.5 m high, causing increased resistance, leading to the uncontrolled flat spin. After release, the glider rose to about 2 m and struck the ground.