Small aircraft experiences power loss. Unable to maintain altitude. Emergency landing.

Attributes
ACN	181868
Time
Date	199106
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : mkg
State Reference	MI
Altitude	agl bound lower : 0 agl bound upper : 2000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	general aviation : personal
Make Model Name	Small Aircraft, High Wing, 1 Eng, Fixed Gear
Flight Phase	cruise other
Flight Plan	None
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : private
Experience	flight time last 90 days : 20 flight time total : 270 flight time type : 200
ASRS Report	181868
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other other : unspecified cockpit
Resolutory Action	flight crew : declared emergency other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

The small aircraft experienced sudden power loss and vibration while on VFR flight at 2000' AGL. A magneto check application of carburetor heat produced no improvement. Altitude could not be maintained. A suitable forced landing field was idented, and an approach was initiated at 1000' AGL. The subsequent landing in the weed/grass covered field produced no perceptable damage to the aircraft or field (or pilot). Removal, in the field, of the #3 cylinder showed that the exhaust valve head had separated from the stem and had destroyed the piston and cylinder head. The engine had approximately 400 hours smoh at the time of the failure. Overhaul records have not been located to determine if new exhaust valves were used in the overhaul. The aircraft was trailered back to it's st louis base.

Original NASA ASRS Text

Title: SMA EXPERIENCES POWER LOSS. UNABLE TO MAINTAIN ALT. EMERGENCY LNDG.

Narrative: THE SMA EXPERIENCED SUDDEN PWR LOSS AND VIBRATION WHILE ON VFR FLT AT 2000' AGL. A MAGNETO CHK APPLICATION OF CARB HEAT PRODUCED NO IMPROVEMENT. ALT COULD NOT BE MAINTAINED. A SUITABLE FORCED LNDG FIELD WAS IDENTED, AND AN APCH WAS INITIATED AT 1000' AGL. THE SUBSEQUENT LNDG IN THE WEED/GRASS COVERED FIELD PRODUCED NO PERCEPTABLE DAMAGE TO THE ACFT OR FIELD (OR PLT). REMOVAL, IN THE FIELD, OF THE #3 CYLINDER SHOWED THAT THE EXHAUST VALVE HEAD HAD SEPARATED FROM THE STEM AND HAD DESTROYED THE PISTON AND CYLINDER HEAD. THE ENG HAD APPROX 400 HRS SMOH AT THE TIME OF THE FAILURE. OVERHAUL RECORDS HAVE NOT BEEN LOCATED TO DETERMINE IF NEW EXHAUST VALVES WERE USED IN THE OVERHAUL. THE ACFT WAS TRAILERED BACK TO IT'S ST LOUIS BASE.

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.