Commercial aviation has a remarkable safety record. The recent engine mishap involving UA328 out of Denver on Feb. 20th is a humbling reminder that not all events are predictable even when we test for them.
The FAA (FAR Part 33 Airworthiness Standards) requires fan blade containment certification tests with no fragments released through the engine containment structure. The pics show the blade containment structure did just that. The FAA acknowledges that secondary events “cannot be precisely predicted.” A blade-off test is typically conducted by explosively discharging a fan blade at the root with the engine on a test stand at takeoff RPM. While a reasonable simulation, there is no way to “test” for every possible scenario associated with catastrophic fan blade failure modes. We are all thankful that this most recent event resulted in no injuries.