Altitude deviation excursion from clearance altitude while GA pilot tried to correct partial power l...

Attributes
ACN	129742
Time
Date	198912
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : bal
State Reference	MD
Altitude	msl bound lower : 6000 msl bound upper : 6000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : ord
Operator	general aviation : personal
Make Model Name	Small Aircraft, High Wing, 1 Eng, Fixed Gear
Flight Phase	cruise other
Route In Use	enroute airway : v308
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : private
Experience	flight time last 90 days : 14 flight time total : 245 flight time type : 245
ASRS Report	129742
Person 2
Affiliation	Other
Function	other personnel
Qualification	other other : other
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted none taken : unable
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I was level at 6000' when the engine lost some power. The engine stayed running in the green arc, but was not putting out full power. In the time I was trying to identify the problem, I lost 600'. This happened approximately 3.5 hours into the flight. Run-up was entirely normal. RPM drop during the magnetic check was 75-100 for both magnetos (maximum allowed is 125). During the first 4 hours of the flight, the engine was normal, with no indication of any problems. When carburetor heat was applied, there was no engine roughness and no improvement when it was taken out. I enriched the mixture, which also had no effect. The remainder of the flight (30 mins) continued like this, and I was able to return to my assigned altitude, and RPM stayed in the green arc. I continued on to the destination. When the FBO inspected the engine, they found no problem with the engine components, except they did find lead buildup on the spark plugs, which they cleaned. Also, when they refueled the airplane, it took 42 gals. This means that the flight down took 42 gals when it should have only required 36 gals. For some reason, fuel consumption was very high. I experience no problems on the 3-HR return flight.

Original NASA ASRS Text

Title: ALT DEVIATION EXCURSION FROM CLRNC ALT WHILE GA PLT TRIED TO CORRECT PARTIAL POWER LOSS. ACFT WAS SMA AND HAD BEEN AT CRUISE ALT FOR 3.5 HRS WHEN SLIGHT LOSS OCCURRED.

Narrative: I WAS LEVEL AT 6000' WHEN THE ENG LOST SOME PWR. THE ENG STAYED RUNNING IN THE GREEN ARC, BUT WAS NOT PUTTING OUT FULL PWR. IN THE TIME I WAS TRYING TO IDENT THE PROB, I LOST 600'. THIS HAPPENED APPROX 3.5 HRS INTO THE FLT. RUN-UP WAS ENTIRELY NORMAL. RPM DROP DURING THE MAG CHK WAS 75-100 FOR BOTH MAGNETOS (MAX ALLOWED IS 125). DURING THE FIRST 4 HRS OF THE FLT, THE ENG WAS NORMAL, WITH NO INDICATION OF ANY PROBS. WHEN CARB HEAT WAS APPLIED, THERE WAS NO ENG ROUGHNESS AND NO IMPROVEMENT WHEN IT WAS TAKEN OUT. I ENRICHED THE MIXTURE, WHICH ALSO HAD NO EFFECT. THE REMAINDER OF THE FLT (30 MINS) CONTINUED LIKE THIS, AND I WAS ABLE TO RETURN TO MY ASSIGNED ALT, AND RPM STAYED IN THE GREEN ARC. I CONTINUED ON TO THE DEST. WHEN THE FBO INSPECTED THE ENG, THEY FOUND NO PROB WITH THE ENG COMPONENTS, EXCEPT THEY DID FIND LEAD BUILDUP ON THE SPARK PLUGS, WHICH THEY CLEANED. ALSO, WHEN THEY REFUELED THE AIRPLANE, IT TOOK 42 GALS. THIS MEANS THAT THE FLT DOWN TOOK 42 GALS WHEN IT SHOULD HAVE ONLY REQUIRED 36 GALS. FOR SOME REASON, FUEL CONSUMPTION WAS VERY HIGH. I EXPERIENCE NO PROBS ON THE 3-HR RETURN FLT.

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.

Altitude deviation excursion from clearance altitude while GA pilot tried to correct partial power loss. Aircraft was small aircraft and had been at cruise altitude for 3.5 hours when slight loss occurred.