Accident Summary
On July 6, 1998, at 13:40 local time, a JAK-52 aircraft, registration LY-BJK, performed an emergency landing with the landing gear retracted at Kyviskiai aerodrome. The aircraft was part of a three-plane formation demonstration flight over Vilnius for State Day. The group had departed from the aerodrome at 12:50.
After the demonstration, the formation returned to Kyviskiai. When the pilot selected the landing gear to extend, the left main gear remained retracted, indicated by a red warning light and mechanical indicator. The pilot attempted emergency gear extension multiple times and performed maneuvers with g-loading to dislodge the gear, all without success. With fuel reserves diminishing, the pilot retracted the right gear and executed a belly landing on the grass runway.
Injuries and Damage
The pilot was uninjured. The aircraft sustained minor damage: both propeller blades were broken at the tips (remaining root sections of 40 cm and 60 cm), both landing gear doors were deformed, and the left gear's retracted-position locking hook was deformed. No damage occurred to third parties or property.
Aircraft and Pilot Information
The aircraft was a single-engine, two-seat JAK-52, manufactured by AEROSTAR, Bacau, Romania, on September 27, 1986. It had a total of 739.57 flight hours and 2,288 landings since new. The pilot, born in 1956, held a private pilot license issued July 3, 1996, valid until June 12, 1999, with type ratings for JAK-18T, JAK-50, and JAK-52, and aerobatic endorsement. He had 1,508 total flight hours, including 675 on the JAK-52.
Weather and Aerodrome
Actual weather at the time: wind 210° at 5 m/s, visibility more than 8 km, cloud cover 7-8 octas at 1,700 feet, temperature 17°C, QNH 999 hPa. Kyviskiai aerodrome has a paved runway (600x30 m, magnetic headings 38° and 318°) and a grass runway (1,000x100 m, headings 160° and 340°). The emergency landing was conducted on the grass runway, which was in good condition with mowed grass.
Investigation Findings
Post-accident inspection revealed that the left main gear's air cylinder, which unlocks the retracted-position hook, did not operate. Disconnecting the air supply tube at the cylinder connection showed the tube was completely clogged. The tube had a diameter of 4 mm. The blockage material was extracted and analyzed. Laboratory tests (microscopic, microchemical, spectroscopic, X-ray electron spectroscopy, gas chromatography-mass spectrometry) identified the contaminants as weakly acidic, composed mainly of amorphous iron and aluminum compounds (mostly hydroxides) with copper compounds and trace carbonates. Additionally, the sample contained soil mineral particles (0.05 to 0.9 mm), paint film fragments (0.005 to 2.2x3.3 mm in various colors), and two plant particles (one a 2.3x1.5 mm birch seed fragment). The source of the contamination could not be determined; it was suspected to have occurred during maintenance at UAB Termikas, but this could not be confirmed.
Emergency Response
Before landing, a rescue team with fire extinguishers, crowbars, and other equipment was positioned at the expected touchdown point. However, the landing was successful and their assistance was not required.
Probable Cause
The probable cause is an emergency landing with the landing gear retracted due to the failure of the left main landing gear to extend. The left main landing gear failed to extend because the air cylinder port was blocked by mechanical impurities.
Recommendations
The investigation commission recommended that all owners/operators of JAK-50, JAK-52, JAK-18T, and JAK-18A aircraft perform a one-time inspection of the air system to ensure cleanliness; and that at the slightest suspicion of landing gear extension/retraction system malfunction, the system should be checked.