I think we’re in heated agreement about the technicalities of what various things measure and those measurements’ correspondence or otherwise with various times recorded for regulatory purposes.
Not sure what flight and duty times have to do with a privately hired GA aircraft. But I take your point in the case of pilots logging flight time on the basis of a steam driven GA tacho that is, on ‘average’, run below the RPM at which 1 tacho hour equals 1 real hour, the logged flight time will usually be less than actual flight time. However, I reiterate that - as always - so much depends on what specific kind of tacho is fitted to the aircraft. Digital tachos don’t work the same as steam driven ones. And a steam driven tacho (and most ‘Hobbs’ meters) will record time spent warming up then taxiing to the fuel bowser to fill up before a flight, none of which time counts as flight time for the pilot nor time in service for the aircraft.
(And I still have no idea how logging tacho time as pilot flight time results in “wasting TBO hours” as suggested by India Four Two.)
Last edited by Lead Balloon; 27th Feb 2022 at 01:08.