FlyVmo. You are quite right. However in the real world of general aviation it is often the case where charter pilots (and others who should know better)will stubbornly elect to try and clear fouled plugs by operating the offending engine at high power for as long as it takes to get the magneto drop back within limits. The fact the drop may be due to a defective magneto ( in which case high power run up's will not rectify the problem), rather than fouled plugs, escapes these people.
