What happened
On 17 September 2003, a Streak Shadow SA, registration G-TTOY, was performing a private takeoff from Runway 2HD at Old Sarum, Wiltshire. During the early stages of the takeoff roll on the grass surface, the aircraft encountered a slight bump. Immediately following this, the pilot experienced a collapse of the right landing gear.
The pilot attempted to abort the takeoff, using the ailerons to keep the wing elevated. However, as the aircraft's speed decreased, the landing gear leg folded backward. This caused the aircraft to veer toward the right and come to a stop just off the edge of the runway. The impact of the gear's movement crushed the top of the underfuselage slipper fuel tank, resulting in a fuel leak. The pilot and passenger evacuated the aircraft carefully to avoid the risk of fire.
The investigation
Investigators examined the right main wheel and brake assembly, discovering that the assembly had separated from the landing gear strut. The separation occurred at a weld connecting the stub axle to the strut lower fitting. As the aircraft settled, the exposed strut dug into the grass, forcing the gear to twist rearward and upward. This motion caused the landing gear cross member to puncture the slipper tank.
Technical analysis of the failed weld revealed that while the external appearance seemed normal, the internal fusion was extremely poor. The effective cross-section of the weld at the interface was as narrow as 1 mm. Metallurgical examination further showed that a progressive fracture had been spreading through this narrow section prior to the final failure.
To determine if this was an isolated incident, the AAIB examined eight other landing gear fittings from various decommissioned aircraft. Every single sample examined showed significant weld deficiencies, including inadequate fusion and insufficient penetration, suggesting a widespread manufacturing issue.
Findings
- The primary cause of the failure was poor weld quality in the landing gear lower fitting, which significantly reduced its structural strength.
- A progressive fracture had weakened the already narrow working section of the weld.
- The landing gear failure caused the gear to rotate rearward, which inevitably crushed the slipper tank due to its mounting position.
- The defects were not detectable through visual inspection or standard dye penetrant testing.
Safety action
Following the investigation, the UK Civil Aviation Authority, working with the BMAA and PFA, issued directives to address the risks. These included a prohibition on using the underfuselage slipper tank due to its vulnerability to fracture during gear incidents. Operators were required to install modified or new undercarriage components to ensure the continued safe operation of the aircraft type.