912ULS Exrended TBO

 What do you mean by "Service Time"???

How do you perceive this is different from TBO???

Rotax engines only have one "Clock" called "Operational Hours".  If the engine is running, the clock is running. Period!

When the Operational clock reaches 2000, you are at TBO.

A basic Hobbs meter activated by an Oil Pressure Switch records the Operational time as intended. 

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From the Line Maintenance Manual

Operational Hours:  All time during which the engine is running is counted towards the total number of operating hours.
- The time is counted irrespective of the load factor of the engine, such as idling or take-off power.

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There are no independent Hobbs Times, Tach Time, Maintenance Time, or any other "Time".

Bill- not true.  TBO is specified in both operational hours and calendar time since first put into service.  Per the Rotax Maintenance Manual, TBO for newer 912ULS engines is 2000 hours or 15 years, whichever comes first.  Per the original question, if you are able to extend your TBO from 1500 hours to 2000 hours per the appropriate SBs, I have not seen anywhere in these SBs allowing further the extension of the calendar TBO from 12 years to 15 years.

When TBO is extended, you extend both the Operational hours and the Calendar time - and TBO expiry is still "whichever comes first". Bill is correct in stating that there is only one kind of "Operational hours".

see 

https://legacy.rotaxowner.com/si_tb_info/serviceb/sb-912-057-ul.pdf

https://legacy.rotaxowner.com/si_tb_info/serviceb/sb-912-041-ul.pdf

Does anybody actually overhaul a low time engine simply because the calendar date has been reached? Are there actually enforcement agencies that require it to be done? This whole calendar time thing seems to me to be little more than a CYA move, which I understand from Rotax's perspective.

The Rotax 15 year calendar time is set due to aging/breakdown of the material in the crankshaft seals, according to the Scandinavian authorized Rotax distributor. At least that is what he said.

The matter was discussed during a Line Maintenance training course I attended.