Japan Airlines Flight 123 (1985)
This Boeing 747 crash resulted in a whopping 520 fatalities. It remains one of the most horrendous single-aircraft accidents in aviation history. This led to necessary improvements in maintenance and better structural design in aircraft. Only twelve minutes after takeoff, “the pressure differential increased to the point that the fatally compromised aft pressure bulkhead could no longer hold itself together. The skin ripped open along the joint between the repaired section and the original bulkhead, and within milliseconds the pressurized cabin air blasted through the gap with tremendous force.” Many engineers had to reconsider the design of the bulkhead to prevent a catastrophe like this one from ever happening again (Medium).