GA small aircraft declared an emergency flying IMC because his engine became rough.

Attributes
ACN	171499
Time
Date	199102
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : nlc
State Reference	CA
Altitude	msl bound lower : 8000 msl bound upper : 8000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : nlc
Operator	general aviation : personal
Make Model Name	Small Aircraft, High Wing, 1 Eng, Fixed Gear
Flight Phase	cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : cfi
Experience	flight time last 90 days : 10 flight time total : 600 flight time type : 4
ASRS Report	171499
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : critical inflight encounter : weather
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : declared emergency other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

While flying in IMC engine roughness occurred with dramatic loss of power. I declared an emergency to the lemoore approach controller. Visibility was marginal below the ceiling as I descended out of the clouds. The controller vectored me to O18. I highly suspect carburetor ice. Mechanics found the carburetor heat ducting crimped so that even with a positive drop in RPM during runup, inadequate heat reached the carburetor. I was grateful for the service provided by the controller due to marginal VFR conditions. Because of the severity of the WX and the lowering of the freezing level. I feel that my decision was correct. Again, I'm grateful for the radar vectors provided to me by lemoore approach facility.

Original NASA ASRS Text

Title: GA SMA DECLARED AN EMERGENCY FLYING IMC BECAUSE HIS ENGINE BECAME ROUGH.

Narrative: WHILE FLYING IN IMC ENG ROUGHNESS OCCURRED WITH DRAMATIC LOSS OF PWR. I DECLARED AN EMER TO THE LEMOORE APCH CTLR. VISIBILITY WAS MARGINAL BELOW THE CEILING AS I DSNDED OUT OF THE CLOUDS. THE CTLR VECTORED ME TO O18. I HIGHLY SUSPECT CARB ICE. MECHS FOUND THE CARB HEAT DUCTING CRIMPED SO THAT EVEN WITH A POSITIVE DROP IN RPM DURING RUNUP, INADEQUATE HEAT REACHED THE CARB. I WAS GRATEFUL FOR THE SVC PROVIDED BY THE CTLR DUE TO MARGINAL VFR CONDITIONS. BECAUSE OF THE SEVERITY OF THE WX AND THE LOWERING OF THE FREEZING LEVEL. I FEEL THAT MY DECISION WAS CORRECT. AGAIN, I'M GRATEFUL FOR THE RADAR VECTORS PROVIDED TO ME BY LEMOORE APCH FAC.

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.