THY wrote:
Could the simple reason for this be that an engine spends a lot more time in cruise than the 5 seconds during “first power reduction”.
Absolute could be – as many other causes.
But doesn’t change the fact that “most engine failures occur at first power reduction” is simply BS.
Most of my students engines failures occur right around first power reduction… But that might be because the altitude for power reduction is also the one their school says is the lowest that I may simulate a failure.
There are certainly potential mechanisms for a power-setting-change induced failure, especially if the change is made quickly.
Crankshaft/conrod stress change due to the counterweights comes to mind.
Crankshaft/conrod stress change due to the counterweights comes to mind
Obviously not the most prevalent reason but seeing the sort of damage counterweights can cause following a rapid power reduction is the sort of practical knowledge that never seems to be taught in ground school.
It certainly can’t be the main reason for engine stoppages. Tongue in cheek, most of them must be due to excess air in the fuel system (known as empty tanks) 
But it is possible that the – very rare – catastrophic failures – example of a magnificently handled one – have this as a statistically significant factor.
