Agree, but if fatigue, one would think it failed at less than designed for load?
bear
I'm not sure what you mean
Fatigue starts accumulating damage at stresses far below the yield strength and if rapidly cycled load are applied (vibatory) there is a Goodman" diagram of fatigue life vs static stress coupled with vibratory stresses
Major aircraft structures often are designed with a 150-200% margin against design limit static overloads, but still will fatigue operating at only 20% of that load.
In the quest to make light weight planes that can carry large fuel loads over long distances, even static load fatigue is an expectation requiring either life limits or inspections for the rest of their life to detect cracks before they seriously reduce the design margin of 150-200% mentioned above.
Add in an abnormal vibratory stress (buffeting, severe turbulence, rough landings etc.) and you may have to inspect more often based on specific in-service experience. All this is captured under "Continued Airworthiness" actions and reflected in constant updating of Service Bulletins etc.