In practice, it makes almost no difference to what you're going to pay after the flight. If you're getting charged airswitch time, you can be certain the rate will be higher than for engine time charges.
If I guess J0N0's local aeroclub correctly, the last time I flew there, their engine switches were all linked to oil pressure, and so only count the time when the engine is running. Never seen one like Buzzy's that started ticking when the master switch was turned on, but I can imagine that some dodgy operator might try such a trick.
Last edited by Unhinged; 27th Apr 2009 at 08:08.