A crack in the landing gear of a Boeing 747

During maintenance operations, a crack was discovered in one of the Boeing 747's main landing gear. The Ministry of Transportation (MOT) was appointed to investigate the cracking phenomenon. IFA performs for the MOT the laboratory tests and the investigation of the failure. The crack was opened in a workshop under laboratory supervision and the submerged section was transferred to a laboratory for examination.

On the surface of the crack an indication of time-dependent crack emanating from the hidden inner wall, out to the visible side, was revealed. Electron microscopy revealed that the initial crack was of brittle and intergranular appearance and leans against the inner wall of the sleeve, in an area that serves as the tightening spring seat. Chemical analysis of the fracture surface indicated the presence of contaminants typical of steel coating, which penetrated into the open crack. This fact is a clear indication that the crack was already opened during coating procedure at the manufacturer depot.