What happened
On March 9, 2006, at approximately 16:00 local time, a Grob G 102 Standard Astir III, registration I-IVBP, was performing a maintenance flight at Aosta “Corrado Gex” Airport. Upon reaching the release altitude of 800 meters, the pilot attempted to retract the landing gear as per standard procedure. During the retraction process, the linkage mechanism failed, leaving the gear stuck in the retracted position.
Following established procedures for such an emergency, the pilot performed a landing on runway 2/20 with the gear retracted. The landing resulted in minor damage to the underside of the aircraft's fuselage and abrasions to the runway surface, but no injuries were reported.
The investigation
The ANSV investigation focused on the mechanical failure of the newly installed landing gear control group. Records showed that the component had been replaced during a 100-hour inspection on February 27, 2006, following a previous deformation caused by a different landing incident. The part in question, part number 102S3-5250, was a new component manufactured by FiberglasTechnik and had not been previously used on any other aircraft.
Laboratory analysis of the fractured part revealed that the failure occurred at the weld point between the plate and the pin. The investigation examined the TIG welding process used during manufacturing, which involves welding without filler material. The analysis identified that the failure was caused by defects within the weld zone.
Findings
- The primary cause of the incident was the instantaneous failure of the landing gear retraction mechanism.
- The failure was attributed to material defects introduced during the manufacturing process.
- Specifically, the welding process used for the pin/plate assembly resulted in defects, such as embrittlement or porosity, which compromised the structural integrity of the component.
- These manufacturing flaws caused the part to fail under standard operational loads during its first use.
Safety action
- The ANSV issued recommendation ANSV-25/88-06/1/I/06 to the European Aviation Safety Agency (EASA).
- The recommendation suggests that if a statistical trend of similar failures is identified, EASA should evaluate a redesign of the component, a revision of the manufacturing process, or the implementation of mandatory non-destructive testing (NDT) for such parts.