A pitts S2B pilot experienced a near midair collision with another aircraft in the pattern at lwm.

Attributes
ACN	809267
Time
Date	200810
Place
Locale Reference	airport : lwm.airport
State Reference	MA
Altitude	msl single value : 1200
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : a90.tracon
Make Model Name	S-2 All Series
Operating Under FAR Part	Part 91
Flight Phase	descent : approach ground : maintenance
Route In Use	approach : visual
Flight Plan	None
Aircraft 2
Controlling Facilities	tracon : a90.tracon
Operator	general aviation : personal
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Phase	descent : approach
Flight Plan	VFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : cfi pilot : commercial pilot : instrument pilot : multi engine
Experience	flight time last 90 days : 8 flight time total : 1370 flight time type : 495
ASRS Report	809267
Events
Anomaly	conflict : nmac
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted
Miss Distance	horizontal : 100 vertical : 100
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

I approached lwm from the north for a fuel stop. I reported a 2 mi right base for runway 23 as instructed by the tower. The pattern was very busy and chaotic with traffic giving airplane rides associated with a charity event (not reported in a NOTAM during my FAA preflight briefing). The tower controller was having difficulty getting the other aircraft to turn from left downwind to left base ahead of me. The controller asked me to turn to 110 degrees; then to a 90 degree heading to avoid the traffic. Despite my diligent scanning; I could not locate the other aircraft. I did not see it until it turned base to final about 100 ft below and 100 ft ahead of me. I followed the aircraft in for an uneventful landing. I should have seen the traffic earlier but did not; despite my concentrated search. I should have maneuvered more to ensure I had a completely unobstructed view. I could also have asked the controller for additional updates on the traffic location; although he was quite preoccupied with the other traffic. A contributing factor may have been my lack of a directional gyro. At times the compass is difficult to interpret while maneuvering in the pitts special. In any case; I believe I turned sufficiently away from my original heading to satisfy the controller's intent.

Original NASA ASRS Text

Title: A PITTS S2B PILOT EXPERIENCED A NMAC WITH ANOTHER AIRCRAFT IN THE PATTERN AT LWM.

Narrative: I APCHED LWM FROM THE N FOR A FUEL STOP. I RPTED A 2 MI R BASE FOR RWY 23 AS INSTRUCTED BY THE TWR. THE PATTERN WAS VERY BUSY AND CHAOTIC WITH TFC GIVING AIRPLANE RIDES ASSOCIATED WITH A CHARITY EVENT (NOT RPTED IN A NOTAM DURING MY FAA PREFLT BRIEFING). THE TWR CTLR WAS HAVING DIFFICULTY GETTING THE OTHER ACFT TO TURN FROM L DOWNWIND TO L BASE AHEAD OF ME. THE CTLR ASKED ME TO TURN TO 110 DEGS; THEN TO A 90 DEG HDG TO AVOID THE TFC. DESPITE MY DILIGENT SCANNING; I COULD NOT LOCATE THE OTHER ACFT. I DID NOT SEE IT UNTIL IT TURNED BASE TO FINAL ABOUT 100 FT BELOW AND 100 FT AHEAD OF ME. I FOLLOWED THE ACFT IN FOR AN UNEVENTFUL LNDG. I SHOULD HAVE SEEN THE TFC EARLIER BUT DID NOT; DESPITE MY CONCENTRATED SEARCH. I SHOULD HAVE MANEUVERED MORE TO ENSURE I HAD A COMPLETELY UNOBSTRUCTED VIEW. I COULD ALSO HAVE ASKED THE CTLR FOR ADDITIONAL UPDATES ON THE TFC LOCATION; ALTHOUGH HE WAS QUITE PREOCCUPIED WITH THE OTHER TFC. A CONTRIBUTING FACTOR MAY HAVE BEEN MY LACK OF A DIRECTIONAL GYRO. AT TIMES THE COMPASS IS DIFFICULT TO INTERPRET WHILE MANEUVERING IN THE PITTS SPECIAL. IN ANY CASE; I BELIEVE I TURNED SUFFICIENTLY AWAY FROM MY ORIGINAL HDG TO SATISFY THE CTLR'S INTENT.

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.