How long should I go on engines?

[Ernie Martin]

I think your course is reasonable. TBO is very meaningful for carriers (like Part 135) who have to abide by them. For Part 91, there is significant merit in using "on condition" criteria similar to that used by major airlines in the maintenance of jet engines. Basically, I monitor the engine as you do -- oil consumption, oil analysis and, for older engines, perhaps double the frequency of compression checks to twice a year -- and fly it as long as all parameters look good.

I do this, in part, because it's a twin. If I had a single engine, I might do things differently, especially if I do a lot of night, IFR or over-water flying.

I don't know exactly what the failure distribution of IO-360 is, but for properly maintained engines and after discarding "infant mortality" events*, it might look like the figure below. 1500 hours marks the point at which failures start becoming frequent, but most engines last for much longer, and mine could be one of those, so I keep them running until there are signs of problems.

Ernie

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* Defective parts or improper assembly will cause some engines to fail very early -- perhaps just hours after overhaul. These failures are due to "infant mortality" and are not considered above. Incidentally, I'd much rather be flying a half-time engine with no sign of problems than one with 20 hours out of overhaul.