What happened
On April 7, 2002, an Ikarus C 42 ultralight aircraft, registration SE-YUK, was performing a landing at Borås/Viared airport in Sweden. The flight had originated from a private airfield near Fjärås, carrying a pilot and one passenger.
As the aircraft touched down on runway 22 and the nosewheel made contact with the pavement, the pilot experienced a sudden loss of control. The left rudder pedal appeared to fail, causing the aircraft to yaw sharply to the right. This sudden movement resulted in the nosewheel strut breaking off, which subsequently caused the aircraft to flip onto its back. Despite the substantial damage to the aircraft, both occupants were uninjured and able to exit the wreckage without assistance.
The investigation
Technical examination of the wreckage focused on the rudder pedal assembly and the nosewheel strut. Investigators discovered that the left rudder pedal, located in the right-hand seat position, had fractured at a welding bead. The fracture originated from a pre-existing crack within the weld of the aluminum pipe. A similar pre-existing crack was also identified on the nosewheel strut.
The investigation traced the mechanical link, noting that force from the left-hand seat pedal is transmitted via a torsion tube to the right-hand seat pedal, which then connects to the rudder cables and nosewheel steering pushrod.
Investigators also reviewed the regulatory landscape. While German manufacturing regulations for this aircraft type required a design load of 300 N for the rudder pedal, Swedish regulations (JAR-22) required a much higher standard of 1000 N. The manufacturer's design load was approximately 500 N. Additionally, the investigation noted that the aircraft had undergone significant repairs to the rudder system and nosewheel strut following a previous accident in 1999.
Findings
- The primary cause of the accident was the failure of the left rudder pedal during the landing sequence.
- A significant contributing factor was that the rudder pedal structure was under-dimensioned relative to Swedish safety requirements.
- The failure was facilitated by a pre-existing crack at a weld on the rudder pedal and the nosewheel strut.
- The investigation highlighted a discrepancy in design standards, noting that the aircraft's construction met German requirements but failed to meet the higher strength standards prescribed by Swedish aviation regulations.