A C152 pilot lost power at cruise altitude, declared an emergency, and landed at sna.

Attributes
ACN	440036
Time
Date	199906
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : sli.vortac
State Reference	CA
Altitude	msl single value : 4500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : sct.tracon tower : txkf.tower
Operator	general aviation : personal
Make Model Name	Cessna 152
Operating Under FAR Part	Part 91
Navigation In Use	other
Flight Phase	cruise : level
Route In Use	enroute other
Flight Plan	VFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : private
Experience	flight time last 90 days : 1 flight time total : 76 flight time type : 50
ASRS Report	440036
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : landed in emergency condition flight crew : diverted to another airport
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

While in cruise flight, I suffered a loss of power and continued power fluctuations to the point where believed sustained level flight may not be possible. No combination of carburetor heat and mixture would restore power (engine was already leaned in accordance with altitude of flight). Cockpit check indicated fuel was on and of sufficient quantity, no problems of any other nature apparent. An emergency was declared and vectors received to a landing at sna. Suspect trouble resulted from lead fouling of spark plugs and discussion with maintenance director indicated that aircraft in question is often flown without being correctly leaned. Also the aircraft had been heavily utilized in the previous 2 days. Performed an extended runup at higher than normal RPM and leaned fully, flight to point of departure was completed safely.

Original NASA ASRS Text

Title: A C152 PLT LOST PWR AT CRUISE ALT, DECLARED AN EMER, AND LANDED AT SNA.

Narrative: WHILE IN CRUISE FLT, I SUFFERED A LOSS OF PWR AND CONTINUED PWR FLUCTUATIONS TO THE POINT WHERE BELIEVED SUSTAINED LEVEL FLT MAY NOT BE POSSIBLE. NO COMBINATION OF CARB HEAT AND MIXTURE WOULD RESTORE PWR (ENG WAS ALREADY LEANED IN ACCORDANCE WITH ALT OF FLT). COCKPIT CHK INDICATED FUEL WAS ON AND OF SUFFICIENT QUANTITY, NO PROBS OF ANY OTHER NATURE APPARENT. AN EMER WAS DECLARED AND VECTORS RECEIVED TO A LNDG AT SNA. SUSPECT TROUBLE RESULTED FROM LEAD FOULING OF SPARK PLUGS AND DISCUSSION WITH MAINT DIRECTOR INDICATED THAT ACFT IN QUESTION IS OFTEN FLOWN WITHOUT BEING CORRECTLY LEANED. ALSO THE ACFT HAD BEEN HEAVILY UTILIZED IN THE PREVIOUS 2 DAYS. PERFORMED AN EXTENDED RUNUP AT HIGHER THAN NORMAL RPM AND LEANED FULLY, FLT TO POINT OF DEP WAS COMPLETED SAFELY.

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.