Sunday Driver -
Couldn't agree more. We had an incident a while ago where a member of our group spotted what seemed to be a hairline crack in the prop. of our 172. It was about 8 inches in from the tip.
If it had been a crack and the prop. had separated in flight, the chances are that the massive out-of-balance forces created by the engine would have shaken the airframe to bits before the engine could be shut down... nasty thought.
We had the prop. taken off and sonically checked with some clever machine that proved, thankfully, that it was no more than a scratch in the metal surface. We think a small stone must have hit the leading edge and split in two, scratching both sides of the prop. and making it look like a crack. It was very hard to see unless you looked very closely, so full marks to the guy who did a thorough pre-flight instead of giving the prop. a cursory glance.
In this case it may have been a false alarm but far better to be safe than sorry....