Originally Posted by
DaveW
So, in the cruise, lean at any altitude unless the POH explicitly says otherwise, and be sure that you're using the POH material that you've read in the intended flight regime.
Its this (key) point that many don't understand (well said DaveW). The problem comes when trying to run the engine at high power settings (i.e. above cruise power) with a leaned mixture. If done correctly at cruise power or lower power settings there will be no issue at whatever density altitude.
I think many operators operate a "lean for taxi" procedure to avoid plug fouling (albeit on hard-standing). When taxiing on hard standing the engine's practically at idle in most cases so leaned almost to ICO mostly presents no problem.
But many (not all) FIs seem to teach PPLs to not touch the Big Red Lever unless starting or shutting down. Its a vital engine control and its usage should be fully taught and understood...
Edited to add - I only speak for NA engines with fixed-pitch props. I have no experience on Turbos nor with CS Props. From what I gather turbo engines are a rather different breed that require very careful handling procedures can differ significantly.