Aloha Airlines Flight 243

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In April 1988, a partial structural failure occurred on a Boeing 737 over the Pacific Ocean while the airplane was en route from Hilo to Honolulu, Hawaii. You can read more about that here:
Aloha Airlines flight 243

There are a number of things that went wrong here, but the National Transportation Safety Board (NTSB), the organization that investigates such events, identified inadequate maintenance on the part of Aloha Airlines as the root cause of the failure. Physically, the accident was enabled by the rapid turnaround and operating environment of inter-island flights. Airplanes' lives can be measured three ways: By calendar time since exiting the factory, by hours in the air, and by the number of takeoff and landing cycles completed. Each of these aging metrics is relevant in different ways, but the number of cycles is most important for fatigue. Each time an airplane is pressurized and it experiences the shudders of turbulence and landing, microscopic damage accumulates in its structure.

The airplanes that Aloha flew between islands spent only an average amount of time off the ground for machines of their pedigree, but the flights were very short, meaning that the planes racked up flight cycles quickly. Add in the warm, tropical air of Hawaii, and the fatigue and corrosion environment was punishing. That said, the NTSB is right that Aloha's maintenance crews should've caught the cracks growing in the skin of this 737 before they coalesced and allowed an 18-foot-long fuselage section to blow out. It's a minor miracle that the flight crew was able to land the aircraft safely on Maui. Similar structural failures occurred in the DeHavilland Comet early in its career, and both times the affected airplane was completely destroyed. The only fatality aboard Aloha 234 was a flight attendant who wasn't strapped down when the fuselage skin departed the airplane.

All things considered, this is a story with a (mostly) happy ending. The airplane was totaled, one woman died, and 65 passengers were injured, but it could easily have been much worse. If nothing else, the accident is now a textbook case of the importance of designing for fatigue, corrosion resistance, and inspectability. Since engineers tend to be visual thinkers and Aloha 234 left behind stunning imagery of failure, I suspect these lessons learned will stick around for quite a while.