Small aircraft develops engine roughness and power loss while in cruise at FL240.

Attributes
ACN	132238
Time
Date	198912
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : phl
State Reference	PA
Altitude	msl bound lower : 24000 msl bound upper : 24000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zny
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Retractable Gear
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : private pilot : instrument
Experience	flight time last 90 days : 112 flight time total : 1961
ASRS Report	132238
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : less severe aircraft equipment problem : critical
Independent Detector	other flight crewa
Resolutory Action	aircraft : equipment problem dissipated controller : issued new clearance
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

En route from bed to ism at FL240, I noticed the tit gauge dropping slightly. I enriched the mixture. Tit returned only for a while, then dropped again. Finally, mixture had reached full rich and fuel flow began to decrease. Engine roughness increased. Fuel selector changed. No change in roughness. Requested lower altitude and to land at nearest ILS airport.I was cleared to phl. As I descended through mid-teen altitudes fuel flow increased; roughness gone. Plane flew normally with no problem after descending to lower altitude. After landing, magnetic check revealed no problem. Moisture in pressurized mags or plugs may have been problem at higher altitude. Flight continued uneventful to ism at 10000'.

Original NASA ASRS Text

Title: SMA DEVELOPS ENGINE ROUGHNESS AND POWER LOSS WHILE IN CRUISE AT FL240.

Narrative: ENRTE FROM BED TO ISM AT FL240, I NOTICED THE TIT GAUGE DROPPING SLIGHTLY. I ENRICHED THE MIXTURE. TIT RETURNED ONLY FOR A WHILE, THEN DROPPED AGAIN. FINALLY, MIXTURE HAD REACHED FULL RICH AND FUEL FLOW BEGAN TO DECREASE. ENG ROUGHNESS INCREASED. FUEL SELECTOR CHANGED. NO CHANGE IN ROUGHNESS. REQUESTED LOWER ALT AND TO LAND AT NEAREST ILS ARPT.I WAS CLRED TO PHL. AS I DSNDED THROUGH MID-TEEN ALTS FUEL FLOW INCREASED; ROUGHNESS GONE. PLANE FLEW NORMALLY WITH NO PROB AFTER DSNDING TO LOWER ALT. AFTER LNDG, MAG CHK REVEALED NO PROB. MOISTURE IN PRESSURIZED MAGS OR PLUGS MAY HAVE BEEN PROB AT HIGHER ALT. FLT CONTINUED UNEVENTFUL TO ISM AT 10000'.

Data retrieved from NASA's ASRS site as of August 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.