What happened
On September 20, 2012, a Bücker Jungmann, registration HB-UVT, was performing a training flight at Lausanne-La Blécherette Airport (LSGL) in Switzerland. The flight involved an instructor and a student pilot conducting circuit training. Following a successful initial circuit, the instructor decided to perform a series of touch-and-go landings.
During the landing phase, the aircraft touched down approximately 100 meters past the runway threshold. After a slight bounce, the aircraft made secondary contact with the ground about ten meters further along. Immediately following this contact, the aircraft began to veer sharply to the right. Despite coordinated efforts from both the student and the instructor to correct the trajectory using rudder inputs, the right wing collapsed toward the ground. The aircraft exited the runway, crossed a taxiway, and came to a stop in a grassy area. There were no injuries to the two occupants, though the aircraft sustained damage to the fuselage, left wing, and landing gear.
The investigation
SESA investigators examined the structural integrity of the landing gear and the aircraft's maintenance history. The investigation focused on the rear attachment of the right main landing gear. Physical examination revealed that the rear attachment sleeve, which was welded to the fuselage structure, had suffered a fracture involving approximately 50% of its circumference.
Technical analysis of the fracture surfaces via microscopy and metallography indicated that the weld quality was poor. The sleeve was composed of a metal with approximately 0.8% carbon content, a material known for being difficult to weld. Investigators also noted that while the aircraft's recent Swiss maintenance records were available, the full technical history prior to its 2007 importation to Switzerland could not be fully reconstructed. Recent maintenance on the landing gear struts had been performed only 16 days before the accident.
Findings
- The primary cause of the accident was a loss of control resulting from the failure of the right main landing gear rear attachment.
- The structural failure was linked to a high-carbon steel weld that provided minimal load-bearing capacity.
- It is possible that pre-existing cracks, potentially caused by operational stresses or previous repairs, propagated until the final sudden rupture.
- The aircraft's weight and center of gravity were within prescribed limits, and meteorological conditions were favorable.