Narrative:

Pleasure flying with friends...climbed through scattered to broken clouds at 4000 ft to 6000 ft to do some brief sight-seeing on top. Descent was steep due to closing gaps in clouds. Throttled back to stay out of yellow arc of airspeed indicator but pushed nose down to expedite descent. I was pitched downward much more than usual, about 30 seconds into descent engine began shaking. Propeller was probably wind-milling. I did a gumps check. Just below 4000 ft I leveled out. I had pulled carburetor heat at first sign of trouble. I throttled up, the engine stumbled a bit then smoothed right out. All egt's and cht's returned to normal. I thought this incident was a classic case of carburetor ice, so I thought nothing of it and proceeded to my destination. The aircraft behaved properly for the remainder of the leg and on the last leg of the trip. But only a couple days later I read an e-mail reflector comment on fuel unporting at steep downward pitches. Thinking back to the incident, I realized several problems: 1) I failed to include the fuel pressure gauge in my gumps scan. 2) carburetor heat was applied when it did very little to help (while throttle was closed). It should have been applied before reducing power. 3) descent through broken layer was stupid. I was going too fast and too steep. I could have called harrisburg approach and requested an IFR clearance.

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Original NASA ASRS Text

Title: A C177 PLT MAKING A RAPID DSCNT THROUGH AN OPENING IN CLOUDS BELOW EXPERIENCES A ROUGH RUNNING ENG UNTIL LEVEL BELOW THE CLOUDS. HIS AFTER THE FACT CRITIQUE OF HIS PROCS AND ACTIONS ILLUSTRATES THE ERRORS MADE.

Narrative: PLEASURE FLYING WITH FRIENDS...CLBED THROUGH SCATTERED TO BROKEN CLOUDS AT 4000 FT TO 6000 FT TO DO SOME BRIEF SIGHT-SEEING ON TOP. DSCNT WAS STEEP DUE TO CLOSING GAPS IN CLOUDS. THROTTLED BACK TO STAY OUT OF YELLOW ARC OF AIRSPD INDICATOR BUT PUSHED NOSE DOWN TO EXPEDITE DSCNT. I WAS PITCHED DOWNWARD MUCH MORE THAN USUAL, ABOUT 30 SECONDS INTO DSCNT ENG BEGAN SHAKING. PROP WAS PROBABLY WIND-MILLING. I DID A GUMPS CHK. JUST BELOW 4000 FT I LEVELED OUT. I HAD PULLED CARB HEAT AT FIRST SIGN OF TROUBLE. I THROTTLED UP, THE ENG STUMBLED A BIT THEN SMOOTHED RIGHT OUT. ALL EGT'S AND CHT'S RETURNED TO NORMAL. I THOUGHT THIS INCIDENT WAS A CLASSIC CASE OF CARB ICE, SO I THOUGHT NOTHING OF IT AND PROCEEDED TO MY DEST. THE ACFT BEHAVED PROPERLY FOR THE REMAINDER OF THE LEG AND ON THE LAST LEG OF THE TRIP. BUT ONLY A COUPLE DAYS LATER I READ AN E-MAIL REFLECTOR COMMENT ON FUEL UNPORTING AT STEEP DOWNWARD PITCHES. THINKING BACK TO THE INCIDENT, I REALIZED SEVERAL PROBS: 1) I FAILED TO INCLUDE THE FUEL PRESSURE GAUGE IN MY GUMPS SCAN. 2) CARB HEAT WAS APPLIED WHEN IT DID VERY LITTLE TO HELP (WHILE THROTTLE WAS CLOSED). IT SHOULD HAVE BEEN APPLIED BEFORE REDUCING PWR. 3) DSCNT THROUGH BROKEN LAYER WAS STUPID. I WAS GOING TOO FAST AND TOO STEEP. I COULD HAVE CALLED HARRISBURG APCH AND REQUESTED AN IFR CLRNC.

Data retrieved from NASA's ASRS site as of July 2007 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.