Engine Failure
Loss of thrust from one or more engines. Whether it becomes an accident usually depends on when it happened and what the crew did next.
Transport aircraft are certified to fly on one engine, so a single engine failure is a manageable event. Accidents arise from uncontained failures that damage other systems, from failures at the worst moment in the takeoff, from both engines failing to a common cause such as fuel or birds, or from the wrong engine being shut down.
"Uncontained" is the word to watch: it means high-energy debris left the engine casing, which is what turns a powerplant problem into a structural and systems problem.
Related terms
A component or system failed in service. The investigation asks why the part failed and why the failure was not contained by design, inspection or redundancy.
A collision with birds, most often during takeoff or approach, and most dangerous when it takes out more than one engine.
From the start of the takeoff roll to a few hundred feet above the runway. Statistically one of the two most dangerous parts of a flight.