Today I was in and out of light rime ice at 11,000 feet. I was watching my manifold pressure for a decrease , inticipatig the use of CARB heat. Instead my manifold pressure went to 25 and then 30 inches at one poit. This went on for about 20 minutes before returning to normal. It seemed to clear up upon reaching warmer temperatures. All other engine indications and sound was normal. It is a 250. Any ideas?

Thanks

Mark

Mark,

Does a download of the engine data show any engine anomalies?

Is the MP gauge traditional or is it now electronic?

Has there been any recent work done?

You were looking for a reduction in MP indicating carb ice and noticed an increase in MP. The increase in MP most likely resulted from moisture in the manifold pressure line freezing. Make sure the drain hole in the low point of the line below the #6 cylinder (I believe that’s the location on a single) is not clogged.

At least you made it back safely. Because of icing in the low levels from the system that stalled over this area, many traveling through the west TN, north AL & MS area Sunday afternoon had to divert to a nearby instrument field.

Charlie, thanks for that explanation. I think that is the most likely cause. I took my plane in for the annual inspection today. My mechanic mentioned this could be a cause. He had a 260 in the hanger with the cowling off and he showed me the manifold pressure line and the drain hole. We didn't look at mine because it was pouring down rain and had to make room in the hanger. I can't remember about the cylinder number but I think you are right. Yes, I was on my way back home from Brownwood, TX to Madison County Executive in Huntsville, Al. I got the ice over Columbus , MS. It was a 4.5 hour flight ending with a GPS approach to minimums. It was good to be back home!

Pat, it is electronic ; JPI 930; no recent work; I got all the way to the airport before I realized I left my thumb drive on my desk, so I haven't downloaded the data yet.

Thanks

Mark