operating cost - what is it based on?

[mattpilot]

Hi

i was wondering what operating cost was based on. I dont want to know what all is included in the costs. I just want to know if its based on Tach time or on Hobbs time?

I figure its kinda based on both. 100h inspections, Overhaul time, and all those other inspections are based on the tach, correct? However, fuel is consumed on a real time basis(hobbs). So half of the operating cost per hour comes from hobbs, and the other from tach - right?

At least thats what i figure - i'm not sure, thats why i'm asking. 'Cause the tach is usually .2 - .4 less than the hobbs and i was just curious.

[JayCeeEll]

On my aircraft :D the maintenance costs are based on the flight time not the hobbs. I am told the reason behind this is because the engine / airframe are not being stressed during taxi and startup!

Although fuel is being used all the time whilst the engine is running its simplest for accounting purposes to use the same times that are used for maintenance.

A suspect larger aircraft use slightly different methods.