Synopsis
On May 26, 2003, at the Biržai aerodrome in Lithuania, a LAK-12 glider (registration LY-GFN) operated by the Biržai aeroclub was involved in a ground incident during a towed takeoff. The glider, towed by a Wilga-35A aircraft, was accelerating for takeoff on a heading of 270°. At approximately 50–60 km/h, the right wing dropped and contacted the grass surface, causing the glider to yaw sharply to the right. The glider pilot disconnected the tow line, and the tow aircraft aborted the takeoff. The glider continued rotating and came to rest about 90° from the original heading.
Injuries
No persons were injured. The glider pilot was wearing a seatbelt and was unharmed.
Aircraft Damage
The glider sustained significant damage to its tail section. The damage included:
- Left stabilizer skin crack (lower area)
- Left elevator skin crack (lower area)
- Left elevator rear section fractured, with the trailing edge broken near the inner rib
- Left stabilizer inner rib crack
- Right stabilizer skin cracks (upper and lower)
- Right stabilizer inner rib crack
- Right elevator skin crack (upper area near inner rib)
- Right stabilizer leading edge crack
No debris separated from the aircraft.
Meteorological Information
At the incident time (15:26 local time), the wind at Biržai was reported by the Lithuanian Hydrometeorological Service as from 110° at 5 m/s (southeast). The aerodrome manager later stated that the wind was from 270°–280° at 4–6 m/s, but the investigation concluded that the wind was from the southeast during the takeoff. The grass on the aerodrome was not mown; its height was 20–30 cm. The takeoff was attempted on a 600 m grass runway oriented 095°×275°, with the takeoff direction 270°.
Investigation
The investigation was not initiated until two weeks after the occurrence, following a media report. The Biržai aeroclub had not notified the investigation authority. By that time, the glider had been removed from the site, and the damaged stabilizer had been taken to the manufacturer for repair. This limited the scope of the investigation.
Conclusions
The investigation found that the glider pilot held a valid license and medical certificate, with significant experience (1,531 total hours). The glider had a valid airworthiness certificate, but its technical service life (set at 468 hours or 5 years from the last overhaul) had expired in 1995 and had not been extended, despite the certificate being renewed multiple times. The flight did not comply with the glider flight manual requirements, which state that takeoff must be conducted strictly into the wind. The aerodrome surface was not adequately prepared for LAK-12 glider operations, as the grass was too tall.
Probable Cause
The cause of the aviation occurrence was an attempt to take off with glider LAK-12 'Lietuva' in a downwind-crosswind condition from a takeoff runway covered with tall grass.