ATR 42-320, G-DRFC
The aircraft suffered a main landing gear collapse following an uneventful approach to land. It was determined that the left side brace upper arm had suffered a fatigue failure. The failure rendered the side brace ineffective and the unrestrained main trunnion continued to translate outboard, leading to the collapse of the gear. The aluminium brace was found to contain a small metallurgical feature at the crack origin which was consistent with titanium rich particles (TiB2) particles which are introduced as a grain refiner during casting of the billet prior to forging. The size of the feature was within the defined specifications for AL7010-T74. Analysis of the area surrounding the crack origin revealed an area of static loading before propagating a crack in fatigue, indicating that there may have been a single overload event at some point in the history of the side brace upper arm. The aircraft manufacturer determined that failure of the brace late in a take-off run is hazardous under EASA certification specification (CS) 25.1309.
Published 10 December 2014