C172 pilot has an engine malfunction and performs an off-field landing.

Attributes
ACN	702139
Time
Date	200607
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl single value : 2500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	general aviation : personal
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	None
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : private
Experience	flight time last 90 days : 30 flight time total : 300 flight time type : 250
ASRS Report	702139
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other flight crewa
Resolutory Action	flight crew : landed as precaution
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

I was coming back direct to ZZZ. 20 mi northwest of ZZZ I encountered a problem -- decrease of FPM engine running erratically -- not normal. I started to lose altitude at that time. My decision was to find a safe place to land -- highway was looking very safe at my location; traffic was at a minimum. I made landing and pulled off the road to the median. After getting back to ZZZ my mechanic checked the aircraft and found that I had extra 8-1/2 gallons of fuel (AVGAS) which was plenty to make the flight to ZZZ; plus reserve for 30 mins. We suspect that carburetor ice was the cause.

Original NASA ASRS Text

Title: C172 PLT HAS AN ENG MALFUNCTION AND PERFORMS AN OFF-FIELD LNDG.

Narrative: I WAS COMING BACK DIRECT TO ZZZ. 20 MI NW OF ZZZ I ENCOUNTERED A PROB -- DECREASE OF FPM ENG RUNNING ERRATICALLY -- NOT NORMAL. I STARTED TO LOSE ALT AT THAT TIME. MY DECISION WAS TO FIND A SAFE PLACE TO LAND -- HWY WAS LOOKING VERY SAFE AT MY LOCATION; TFC WAS AT A MINIMUM. I MADE LNDG AND PULLED OFF THE ROAD TO THE MEDIAN. AFTER GETTING BACK TO ZZZ MY MECH CHKED THE ACFT AND FOUND THAT I HAD EXTRA 8-1/2 GALLONS OF FUEL (AVGAS) WHICH WAS PLENTY TO MAKE THE FLT TO ZZZ; PLUS RESERVE FOR 30 MINS. WE SUSPECT THAT CARB ICE WAS THE CAUSE.

Data retrieved from NASA's ASRS site as of January 2009 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.