Narrative:

On an IFR flight to ZZZ1; I was in and out of clouds as I skimmed the tops of cumulus. The aircraft was performing normally when center asked me to climb to 11000 ft for terrain clearance. I had not been using carburetor heat; but had been in clear air mostly; with bright sunshine. OAT was reading 48 degrees F. As I advanced the throttle to climb; the RPM's dropped alarmingly. I turned on the carburetor heat; and the RPM's dropped even more. The airplane would not climb; and I advised ATC. They switched me to approach. I hesitated; unsure of what to do. Do I give the carburetor heat time to work? I couldn't climb to the higher altitude. While I thought; the controller suggested I turn towards ZZZ as a precaution. I was reluctant to fly an approach because I was unfamiliar with the function of my EFIS. When I told him the engine was not responding; he declared an emergency and directed me to descend and report sighting the airport. The engine was making power; but not full power. I sighted the ground; and was directed to try to get under the clouds; but they were too low. I finally did see the airport; but while circling to land; I lost contact. The controller and I decided an ILS was our best bet; so he began vectoring me for an intercept. I was unable to manage flying and reading the chart; so the controller gave me a surveillance approach. I broke out at 900 ft lined up with a runway; and made an uneventful landing. My unfamiliarity with the localizer depiction on my EFIS prevented me from flying a normal IFR approach. I was uncertain of the correct procedure for applying carburetor heat in IMC.

Google
 

Original NASA ASRS Text

Title: PLT OF SMA ON IFR FLT PLAN HAS PARTIAL ENGINE FAILURE AND NEEDS ATC ASSISTANCE TO LAND AT NEARBY ARPT.

Narrative: ON AN IFR FLT TO ZZZ1; I WAS IN AND OUT OF CLOUDS AS I SKIMMED THE TOPS OF CUMULUS. THE ACFT WAS PERFORMING NORMALLY WHEN CTR ASKED ME TO CLB TO 11000 FT FOR TERRAIN CLRNC. I HAD NOT BEEN USING CARB HEAT; BUT HAD BEEN IN CLR AIR MOSTLY; WITH BRIGHT SUNSHINE. OAT WAS READING 48 DEGS F. AS I ADVANCED THE THROTTLE TO CLB; THE RPM'S DROPPED ALARMINGLY. I TURNED ON THE CARB HEAT; AND THE RPM'S DROPPED EVEN MORE. THE AIRPLANE WOULD NOT CLB; AND I ADVISED ATC. THEY SWITCHED ME TO APCH. I HESITATED; UNSURE OF WHAT TO DO. DO I GIVE THE CARB HEAT TIME TO WORK? I COULDN'T CLB TO THE HIGHER ALT. WHILE I THOUGHT; THE CTLR SUGGESTED I TURN TOWARDS ZZZ AS A PRECAUTION. I WAS RELUCTANT TO FLY AN APCH BECAUSE I WAS UNFAMILIAR WITH THE FUNCTION OF MY EFIS. WHEN I TOLD HIM THE ENG WAS NOT RESPONDING; HE DECLARED AN EMER AND DIRECTED ME TO DSND AND RPT SIGHTING THE ARPT. THE ENG WAS MAKING PWR; BUT NOT FULL PWR. I SIGHTED THE GND; AND WAS DIRECTED TO TRY TO GET UNDER THE CLOUDS; BUT THEY WERE TOO LOW. I FINALLY DID SEE THE ARPT; BUT WHILE CIRCLING TO LAND; I LOST CONTACT. THE CTLR AND I DECIDED AN ILS WAS OUR BEST BET; SO HE BEGAN VECTORING ME FOR AN INTERCEPT. I WAS UNABLE TO MANAGE FLYING AND READING THE CHART; SO THE CTLR GAVE ME A SURVEILLANCE APCH. I BROKE OUT AT 900 FT LINED UP WITH A RWY; AND MADE AN UNEVENTFUL LNDG. MY UNFAMILIARITY WITH THE LOC DEPICTION ON MY EFIS PREVENTED ME FROM FLYING A NORMAL IFR APCH. I WAS UNCERTAIN OF THE CORRECT PROC FOR APPLYING CARB HEAT IN IMC.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.