landing gear
I remember the port main gear fell out over puchong in malaysia due to an incorrectly sized gland nut fitted to the main oleo strut.The a/c..a B737-200 made a perfect landing ..the crew had 3 greens so were unaware till touchdown!
Boeing along with other a/c types have a litany of problems which manifest themselves over time as the a/c type ages..and the occasional lapse in maintainence and equipt fails !!!