Temporary Total Loss of Power

Yes, fuel pump and carb heat were on during the approach (as always). Carb goes to WOT if linkage fails (another pilot experienced that already in the past on another a/c of the same type, causing a very rough running engine and the need to cut power for landing).

And just a little follow-up: Maintenance couldn't identify any problem with the engine. The a/c now flew about 40 hrs after this incident without any problems (I personally preferred not to fly it). So it all remains very mysterious to me.

Rotax-Owner wrote:

I wouldn't factor your oil PSI into what occurred due to it still being within range. Depending on your S/N range you are allowed to be @ 1.5bar when above 3500RPM.

I would focus more on the carb heat and electric fuel pump activation. When you turned on your carb heat, your engine went into a very rich running condition and when you turned on the E-pump at the same time, you may have exaggerated it even further if your floats are even slightly heavy (7.0g). It is not necessary to turn on the carb heat when you are on the final approach as you would on a conventional aircraft (Cont/Lycom). 

This was a major topic of discussion with flight schools who switched from Cessna's to the Rotax-powered Diamond aircraft and they were constantly pulling carb heat on the final approach as this would turn the carburetors and spark plugs jet black due to how rich the engine was running. There were occasions when the engine lost power when doing this. 

Check your floats to make sure they are within spec and try to avoid pulling carb heat unless it is necessary! 

One more follow-up: Yesterday we had a meeting with a Rotax expert and as it looks, the low oil pressure and the power loss were two separate incidents. The only common denominator was the high ambient temperature on that day.

High oil temperature together with an oil level just slightly above the minimum marker could have caused the short and transient low oil pressure warning that we got. The recommendation we got is to fill up oil to at least 1/2 (i.e. between min and max) on hot days for better cooling and to get less viscosity drop and pressure drop.

The theory regarding to the power loss now is, that the engine was running already very rich due to the high OAT and this was even exaggerated by switching on carb heat. This basically caused the motor to drown. Applying full throttle thankfully cleared the motor, so that it caught on after about 20 seconds. The recommendation we got is NOT to use carb heat when the OAT is high.

Unfortunately, our checklist says: carb heat ON for landing. So, not pulling carb heat would be in violation of the checklist. But I think, that above 20°C OAT there should be no risk for icing for the Rotax. Especially if we pull carb heat for a short period of time to check if any ice is melting.