A C150 pilot landed short of hwd due to engine roughness.

Attributes
ACN	621886
Time
Date	200406
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : hwd.airport
State Reference	CA
Altitude	msl bound lower : 50 msl bound upper : 1000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : hwd.tower
Operator	general aviation : personal
Make Model Name	Cessna 150
Operating Under FAR Part	Part 91
Flight Phase	descent : approach landing : roll
Flight Plan	VFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : private
Experience	flight time last 90 days : 35 flight time total : 480 flight time type : 480
ASRS Report	621886
Person 2
Affiliation	government : faa
Function	controller : local
Events
Anomaly	aircraft equipment problem : critical non adherence : published procedure non adherence : far
Independent Detector	other flight crewa
Resolutory Action	flight crew : landed as precaution flight crew : landed in emergency condition
Consequence	other
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

I was cleared to land at hwd, when I experienced engine problems -- the engine began to run rough. Not wishing to pass up a good landing site, and possibly endangering myself and others, I performed a precautionary landing at a vacant field in an industrial area of union city. The field was freshly mowed grass about 1200 ft long. The landing was good and no one was injured and the airplane was not damaged. Further flight was not an acceptable option because the flight path would have taken me into an area that was increasingly residential. 2 days later, the mechanic came to take the wings off to transport the aircraft out of the area. Upon draining the wings of fuel, he found that at the time of the incident, there was 5.0 to 5.5 gals remaining in the tanks. Since there are 3.5 gals of unusable fuel, the aircraft had 1.5 to 2.0 gals of useable fuel remaining in the tanks. This confirmed that the reason the engine ran rough was possibly caused by carburetor icing. Once the engine started running rough, I checked the fuel shutoff, cycled the carburetor heat, and checked the magnetos. The engine continued to run rough, forcing a precautionary landing.

Original NASA ASRS Text

Title: A C150 PLT LANDED SHORT OF HWD DUE TO ENG ROUGHNESS.

Narrative: I WAS CLRED TO LAND AT HWD, WHEN I EXPERIENCED ENG PROBS -- THE ENG BEGAN TO RUN ROUGH. NOT WISHING TO PASS UP A GOOD LNDG SITE, AND POSSIBLY ENDANGERING MYSELF AND OTHERS, I PERFORMED A PRECAUTIONARY LNDG AT A VACANT FIELD IN AN INDUSTRIAL AREA OF UNION CITY. THE FIELD WAS FRESHLY MOWED GRASS ABOUT 1200 FT LONG. THE LNDG WAS GOOD AND NO ONE WAS INJURED AND THE AIRPLANE WAS NOT DAMAGED. FURTHER FLT WAS NOT AN ACCEPTABLE OPTION BECAUSE THE FLT PATH WOULD HAVE TAKEN ME INTO AN AREA THAT WAS INCREASINGLY RESIDENTIAL. 2 DAYS LATER, THE MECH CAME TO TAKE THE WINGS OFF TO TRANSPORT THE ACFT OUT OF THE AREA. UPON DRAINING THE WINGS OF FUEL, HE FOUND THAT AT THE TIME OF THE INCIDENT, THERE WAS 5.0 TO 5.5 GALS REMAINING IN THE TANKS. SINCE THERE ARE 3.5 GALS OF UNUSABLE FUEL, THE ACFT HAD 1.5 TO 2.0 GALS OF USEABLE FUEL REMAINING IN THE TANKS. THIS CONFIRMED THAT THE REASON THE ENG RAN ROUGH WAS POSSIBLY CAUSED BY CARB ICING. ONCE THE ENG STARTED RUNNING ROUGH, I CHKED THE FUEL SHUTOFF, CYCLED THE CARB HEAT, AND CHKED THE MAGNETOS. THE ENG CONTINUED TO RUN ROUGH, FORCING A PRECAUTIONARY LNDG.

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.