In Canada, we have it well-defined he
http://www.tc.gc.ca/CivilAviation/Re...ards/a625c.htm

Scroll down to "6. Engines" and see the note in italics. Do the FARs
have a similar requirement? I couldn't find it, but it's likely there
somewhere.
"Airworthiness" is a legal term meaning "safe and fit for
flight." Doesn't mean "perfect."

Dan