912S3 engine time vs flight time service intervals and TBO

Absolutely. I just saw that too, as written earlier, I think it's important that rotax makes another change in the manual here at the 912. 

Either you do it the way it says in the book, and if everyone doesn't do it by the book, you have to change the book. In this case I think this is only correct.

With TBO of 2000h after engine running time, one has effectively only between 1200 and 1600h flying hours, depending on whether one flies in a flight school and/or on a large place with long TAXI times... this is neither economical nor does this testify to the high quality which Rotax promises in their advertising in each case.

All. 

Interesting viewpoints on time calculations.  While I do agree with some others are not agreeing with good mechanical logic.  This is a piston engine and unlike turbine and jet engines the most severe wear is in the initial startup and warming of the engine.  Actual running time at power creates very little wear and this is reflected in reduced overall damage.  Time creates a great many issues that are related to aging of parts, mostly the soft parts, along with concerns about long periods of un-use such as storage. Both EASA and the FAA employ basic block testing of engines by both ground testing and then confirmed with fleet testing.  Over long periods of time fleet leader monitoring of controlled use aircraft add to the data points to consider increasing both calendar time and hours.  The actual methods are not arbitrary and are not changed without testing.  Just using 3rd party conjecture is hardly the way to proof actions to increase time or hours on engines used for flight.  Indeed in many applications heavy use of an engine will result in reduction of recommended times for aircraft used in applications such as drop dusting, helicopter and in some cases flight training.  

The concern should be safety of the operations on engine life and it saddens me to see many only looking at the economical impact of spending money to do extra maintenance or overhauls sooner than when they want to.  Engine with gearboxes are particularly prone to failure when used a great deal of time on the ground, low RPM/power application, as this puts undue stress on the parts internally.  i would argue that the proposal for flight hours is driven by commercial concerns and not good mechanical practice.  This comes from the turbine and jet world where running idle on the runway has little to zero effect on the parts internally.  It is my opinion that piston engines, particularly with aa gearbox, should not be lumped into that class without understanding the potential for expensive repairs at a later time. 

Good luck on you quest for a simple answer as i don't believe flight time is actually wise.  We see far too many who can't maintain a gearbox currently and I doubt just adding extra TBO without testing is wise. 

Cheers

I agree with RW. Total run time and not just flight hours. You can't compare some engines to others. That's  apples to oranges for comparison.

Roger Lee wrote:

I agree with RW. Total run time and not just flight hours. You can't compare some engines to others. That's  apples to oranges for comparison.

100% agree with that statement.

However, both 915 and 916 are piston engines and come with a reduction gearbox but on both these engines Rotax is no longer specifying Operating hours as the parameter for Mantenance Interval and TBO definition.

On the B23 Turbo I fly regularly, there is only one counter implemented in the Garmin system and it counts flight hours (i.e. above a certain airspeed).

For sure there can be some internal difference in the Gearbox configuration between the 915/916 and 912 that will justify the different calculation of TBO but it's quite clear this is not simply driven by being a piston engine with a reduction gearbox.

In any case, unless Rotax changes the MM, I believe there is little room to maneuver here. The owner can still define a different AMP but, as far as PART-M is concerned, it doesn't seem possible to be less restrictive than the OEM has defined in the applicable Maintenance Manuals.

Hi All

They type 912 engines with the dog and ram system for damping is very different and limits what can be allowed.  The larger 915 and 916 allowable mass moment of inertia allowed for a propeller has been increased significantly by the new design gearboxes. in the case of defining time determination there are a lot of factors.  The latest 916 manual reflects what the new time definition is.  Clearly the burden is on the OEM to validate the time method to be used for their aircraft type and design.  This follows normal aviation standards that I have seen.  

In the case of certified applications the maintenance schedule is verified by the OEM.  If the OEM simply refers to the Rotax maintenance schedule then that would be what you have to follow.  (at least under FAA and EASA rules) As a note in the FAA (USA) the aircraft used for private and experimental aircraft to go on condition if they determine that is suitable to them.  In the event of civil law disputes, such as an accident, then the rationale for exceeded time would rest with the operator.  It is obvious that pressure from the training fleet in particular has driven some acceptance of flight hours over hobbes time.  in Latin America and a lot of experimental users in the USA logbooks are almost non-existent.  A simple check of used engines for sale shows that is an all too common issue.  

For your reading here is copy of the latest wording used for the type 916 engine as released in the Line Maintenance Manual in July of this year. 

Cheers