Put it this way brainy.
You elect to use the CASA maint schedule 5.
42B1-1.
6.7 Except where otherwise approved or directed by CASA the procedures and limits prepared by the aeroplane manufacturer are to be used when performing an inspection required by this schedule.
42B1-1 does not specifically cover prop, mag, fuel pump periods etc
An example of an AD issued to allow an over run is AD/Prop/1, whereby they
Allow extended periods for Hartzell etc.
If the manufacturers data did not have to be followed in the first place, then why
Would CASA have to issue an AD to allow deviance.
The direction is then, any devience from the data requires direction from CASA.
If you want to deviate from the overhaul limits, this maybe one way, but I'll have to confirm,
As the CofR holder, as you know you are also responsible, if you want to deviate from the limits, you would have to supply me with a written letter, outlining your desire to not conform with the overhaul limits, the approved Data and so on.
Then you would have to guarantee there would be no come back on the maintainer if such component failed, and guarantee no charge of negligence
Bought about by any other party for failing our duty of care.
Then convince a maintainer of such.
otherwise create your own SOM for your aircraft and get it approved by CASA,
But in doing so, you would have to come up with an enormous amount of supporting Data to allow you to deviate from the manufacturers limits.
In this Day and age of litigation, liable, duty of care and so on, how do you think
You would go.
In my experience, with what is found not only at the 500hrly but also at the calendar time, it is worth doing, especially for $4-500 bucks over 4 years.
That's what I would term common sense.