Broken valves can render one cylinder inoperative and produce a rough-running engine. On the IO-520 cylinder above, a crack developed, allowing the intake valve’s seat to come loose. The valve smashed itself into six pieces.

by Thomas P. Turner

Engine failure. Aside from fires, it’s the airborne emergency pilots fear most. We debate the wisdom of flying single-engine airplanes at night, on instruments, through mountains or over water, heralding a second engine as the answer to these “risky” behaviors. Some eschew even piston twins, favoring turbine equipment instead. Whole industries have grown up around engine management techniques and technologies meant to reduce the chance of an engine failure.

This begs two questions: First, what really causes engines to fail? Second, what can we do that is effective in preventing engine failures in our airplanes? …