Originally Posted by
Okihara
I (think that I) know the difference between these two times however when referring an aircraft to a 50 or 100 hourly maintenance, which time should be considered? Hobbs or tach?
50 or 100 hourly maintenance is usually measured as hours 'time in service'. 'Time in service' is usually measured from wheels off the ground to wheels on the ground.
That's not tach time.
It
could be Hobbs time, but only if the Hobbs is connected to an air switch. Many Hobbs meters start counting and keep counting while ever the battery (and maybe master) switch is on.
Same question regarding overhauls. If your aircraft manufacturer states TBO: 2000 hours, is that in Hobbs or in tach time?
That sort of time is usually for engines. If it's for an engine, tach time is the measure.
Also:
– It would seem that in Australia the Hobbs meter is usually called VDO. Is that correct?
Dunno.
The confusion arises because a Hobbs meter is merely a brand. That brand can be connected to a master (and maybe master) switch and counts time while ever it's switched on, or can be connected to an airswitch and measures time in excess of a particular airspeed (based on the assumption that the aircraft is flying while ever that airspeed is exceeded).
– Is the tach time the same as an airswitch?
Nope. Never.
Tach time measures the time the engine is running. (Although it's worth noting that the time recorded on a tach is only accurate when the RPM is at the RPM for which the tach is calibrated. Below that RPM an hour of actual operation will be recorded as a shorter time on the tach, and above that RPM an hour of actual operation will be recorded as a longer time on the tach.)
Airswitch time measures the time from wheels off to wheels on, or pretty close to that.