Up-thread I was raving about the Rotax 912... > there are more complex system interactions than meets the eye which can cause some problems I will grant this

Up-thread I was raving about the Rotax 912... > there are more complex system interactions than meets the eye which can cause some problems I will grant this for sure. Kind of like modern cars though, it's a double-edged sword. On the UAS programme I'm working on it has been absolutely invaluable to be able to just plug into the 912 ECU's CAN bus and gather a ton of engine telemetry (and send it down to the ground for monitoring at the GCS). Thank you for posting the links and starting the discussion about 912 reliability. I'm going to have to dig into it a little and see if there's any takeaways I need to bring back to my team. With zero evidence to support this other than my own experience with N=4 of these, I have a suspicion that part of the problem could be that they're not getting sufficient maintenance and inspection because of how simple they are from an O&M perspective and how robust they are in nominal and off-nominal conditions. When I was first working with it and flipping through the operators manual I was kind of shocked to discover that the only real pre-flight actions are: check coolant level, rotate the prop and make sure the oil reservoir burps. There's a startup and warm-up procedure that we follow to the letter but short-term you almost certainly won't notice if you skip it. Before we had our robust telemetry system and checklists in place, we accidentally flew it with only one ECU lane turned on once and didn't notice until we were on the ground. Engine was already off after landing when someone came on the radio and asked "hey guys... in-flight we're supposed to have both lanes A and B on right?" "Yeah..." "The Lane B switch was off when I approached the aircraft...". To summarize what I'm getting at: this engine, in my experience so far, has a ton of really robust redundancy features and those redundancy features work so well that you may not notice that you've got issues until you've run out of redundancy. I can only think of two situations where we've had issues bad enough that it caused it to "run rough" and trigger a deeper investigation: - Because our aircraft is unmanned we have electromechanical relays in series with the Lane A/B switches that we can control from the ground both for engine-start safety (the engine can't be started unless both the crew chief and remote pilot have turned on Lanes A and B) and to be able to kill the engine remotely after landing or in an emergency. We had an electrical issue that was causing the relays to chatter, resulting in Lanes A and B getting sporadic power. - Somehow in one revision of the ever-evolving full-system checklist the "check water separator" item got dropped and no one noticed. It flew probably 10+ flights on that checklist before we had a really rough start, in an environment that was highly conducive to water accumulation in the fuel (large daily OAT and RH swings). We were horrified at how much water came out when I realized that no one had been checking... and yet there had been zero negative effects until there was a big negative effect.