Sorry if this is an old chestnut, but I can't find it anywhere. How do you determine the 100-hour mark on a 912UL when the Hobbs meter is pressure-switched i.e just records flying hours? Do I just take the Hobbs reading, or should I also record my taxi-time and add that to it? After 100 hours flying there could be a 25 per cent discrepancy which don't sound right.
  • Re: 912 Service interval - how to determine?

    by » 4 years ago


    FAA Definitions:
    “Time in Service. With respect to maintenance time records, means the time from the moment an aircraft leaves the surface of the earth until it touches it at the next point of landing.”

    Thank you said by: Ronald Dobson

  • Re: 912 Service interval - how to determine?

    by » 4 years ago


    Thanks for replying Rob, That is indeed the FAA (and CASA, apparently) definition with which, I believe, Rotax complies in its' maintenance schedule timing. However Conair have told me that it is "Engine on time,regardless of load",so I'm still at a bit of a loss. Obviously,the oil-pressure Hobbs and the air-pressure Hobbs measure different times. I have the air pressure Hobbs, so it makes sense to be working on take-off to landing as you point out. Mustn't it???

  • Re: 912 Service interval - how to determine?

    by » 4 years ago


    Rotax has a different opinion; they say all engine operating hours. See Line maintenance manual 05-10-00 sec 1.2 Operating hours. (I do not agree with this section and have been trying to convince Rotax to change it in accordance with FAA guidelines)
    If you are in the UK then I am not familiar with your regulations but if they copied the FAA then I would for sure use flight time instead of engine run time.
    My opinion: The engine does not wear appreciably during idle/run-up (it has no load, not working hard like in flight)
    The engine is only one part of a simple aircraft; you cannot have one component dictating the maintenance schedule (until you get into big complicated aircraft: airliners, helicopters..)

    Thank you said by: Ronald Dobson

  • Re: 912 Service interval - how to determine?

    by » 4 years ago


    Rotax specify recording the operating hours of the 912 series a bit differently to convention. The details can be found in the Line Maintenance Manual section 05-10-00 paragraph 1.1
    MMLoperatinghours.png (You do not have access to download this file.)

    Thank you said by: Ronald Dobson

  • Re: 912 Service interval - how to determine?

    by » 4 years ago


    Thanks for that, Conrad. Can't argue with black and white, throws a bit of a spanner in the works though. How do you determine engine-on time as per the Rotax definition if the Hobbs records only flying time?

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