China Airlines Flight 611 (2002)
This Boeing 747 crash forced engineers to improve maintenance procedures for older aircraft. Because of metal fatigue in the fuselage, the plane crashed into the Taiwan Strait, killing all 225 people on board. Decades prior, the plane had suffered a tail strike, and since then, improper maintenance caused it to break down. Instead of fixing the issues, engineers simply installed a doubler over the damaged part, much like putting on a bandaid over an infected wound (Simple Flying).