BE33 pilot has near midair collision with C172 on base leg at uncontrolled airport.

Attributes
ACN	788855
Time
Date	200805
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 800
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : zzz.tracon
Operator	general aviation : personal
Make Model Name	Bonanza 33
Operating Under FAR Part	Part 91
Flight Phase	descent : approach
Route In Use	approach : traffic pattern
Flight Plan	None
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : multi engine pilot : instrument pilot : commercial pilot : cfi pilot : private
Experience	flight time last 90 days : 20 flight time total : 3100 flight time type : 1800
ASRS Report	788855
Person 2
Affiliation	other
Function	flight crew : single pilot
Events
Anomaly	conflict : nmac
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action flight crew : executed go around flight crew : exited adverse environment
Miss Distance	horizontal : 150 vertical : 0
Supplementary
Problem Areas	Airport Flight Crew Human Performance
Primary Problem	Ambiguous

Narrative:

Was on a post maintenance check flight; VFR with flight following south of ZZZ1. After maintenance items were checked started to return to home airport; but on spur of the moment decided to divert to ZZZ for practice lndgs. Advised ATC; canceled flight following; made a descending 270 degree turn away from airport; so as to be at pattern altitude while approaching airport. Leveled out about 3.5 mi; made standard 45 degree entry to downwind pattern. ZZZ does not have an instrument approach; so did not have a reference pattern advisory frequency in the approach plates; no time to dig out the sectional; so I scanned for conflicting traffic carefully. As I turned downwind; I saw 1 aircraft just lifting off departure end; nothing else. Continued to look for traffic; configured the aircraft for landing; was stabilized on altitude and airspeed; but may have been (in retrospect) a little wide in the pattern. At the 180 degree; turned for left base and began descent. Before I was wings level for base; saw a C172 pass very close (50 yards or less) from my 8 O'clock position; crossing my flight path just behind me. I abandoned the approach and departed the pattern to home base. Considerations: spur of the moment decision led to improper preparation; even though not required; I did not have the great advantage of being able to query and announce in the pattern. I tried to compensate for this by carefully scanning for aircraft; unsuccessfully. Markings may have helped the aircraft to blend into backgnd.

Original NASA ASRS Text

Title: BE33 PLT HAS NMAC WITH C172 ON BASE LEG AT UNCONTROLLED AIRPORT.

Narrative: WAS ON A POST MAINT CHK FLT; VFR WITH FLT FOLLOWING S OF ZZZ1. AFTER MAINT ITEMS WERE CHKED STARTED TO RETURN TO HOME ARPT; BUT ON SPUR OF THE MOMENT DECIDED TO DIVERT TO ZZZ FOR PRACTICE LNDGS. ADVISED ATC; CANCELED FLT FOLLOWING; MADE A DSNDING 270 DEG TURN AWAY FROM ARPT; SO AS TO BE AT PATTERN ALT WHILE APCHING ARPT. LEVELED OUT ABOUT 3.5 MI; MADE STANDARD 45 DEG ENTRY TO DOWNWIND PATTERN. ZZZ DOES NOT HAVE AN INST APCH; SO DID NOT HAVE A REF PATTERN ADVISORY FREQ IN THE APCH PLATES; NO TIME TO DIG OUT THE SECTIONAL; SO I SCANNED FOR CONFLICTING TFC CAREFULLY. AS I TURNED DOWNWIND; I SAW 1 ACFT JUST LIFTING OFF DEP END; NOTHING ELSE. CONTINUED TO LOOK FOR TFC; CONFIGURED THE ACFT FOR LNDG; WAS STABILIZED ON ALT AND AIRSPD; BUT MAY HAVE BEEN (IN RETROSPECT) A LITTLE WIDE IN THE PATTERN. AT THE 180 DEG; TURNED FOR L BASE AND BEGAN DSCNT. BEFORE I WAS WINGS LEVEL FOR BASE; SAW A C172 PASS VERY CLOSE (50 YARDS OR LESS) FROM MY 8 O'CLOCK POS; XING MY FLT PATH JUST BEHIND ME. I ABANDONED THE APCH AND DEPARTED THE PATTERN TO HOME BASE. CONSIDERATIONS: SPUR OF THE MOMENT DECISION LED TO IMPROPER PREPARATION; EVEN THOUGH NOT REQUIRED; I DID NOT HAVE THE GREAT ADVANTAGE OF BEING ABLE TO QUERY AND ANNOUNCE IN THE PATTERN. I TRIED TO COMPENSATE FOR THIS BY CAREFULLY SCANNING FOR ACFT; UNSUCCESSFULLY. MARKINGS MAY HAVE HELPED THE ACFT TO BLEND INTO BACKGND.

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