What happened
On August 17, 2007, an Airbus A330-200 was taxiing at Munich International Airport. The aircraft departed from stand 113 at Terminal 1, proceeding via taxiways Oscar 1, Chally 4, and Sierra. At approximately 16:00 local time, as the crew initiated a left turn onto taxiway Sierra, the bogie beam of the right main landing gear fractured behind the shock absorber attachment.
The failure caused the rear portion of the bogie beam, including the rear axle and both rear wheels, to separate from the rest of the gear, leaving the assembly connected only by two brake linkages. The aircraft's movement caused the lower end of the shock absorber strut to drag along the taxiway, creating a 42.8-meter furrow in the concrete. The pilot immediately applied the brakes, bringing the aircraft to a halt. All 244 passengers and 15 crew members evacuated the aircraft via stairs provided on the taxiway without injury.
The investigation
The BFU examined the fractured components, which were sent to the United Kingdom for analysis in coordination with the UK Air Accidents Investigation Branch and the component manufacturer. The investigation focused on the fracture surfaces and the integrity of the corrosion protection layers.
Microscopic analysis revealed that the fracture originated from a pit at the 6 o'er position on the inner diameter of the tubular beam. The investigation found that the corrosion protection—a three-layer paint system over a cadmium plating—was insufficient. Measurements indicated that the coating thickness at the 6 o'clock position was below the required specifications. Furthermore, the investigation explored how environmental factors and maintenance fluids might have contributed to the degradation of the protective layers.
Findings
- The primary cause of the failure was stress corrosion cracking originating from a localized pit.
- The crack was initiated by pitting corrosion at the inner bottom surface of the bogie beam.
- The corrosion protection was compromised due to an incomplete coating process where the initial wash primer layer was either too thin or entirely absent in critical areas.
- The degradation of the protective layers was accelerated by a combination of environmental exposure and the presence of various substances, including moisture and chemical agents, which led to the sacrificial depletion of the cadmium plating and subsequent exposure of the high-strength steel to the elements.
- The high mechanical loads applied to the gear during the turning maneuver provided the final stress necessary to propagate the crack through the remaining cross-section.