Piper 140 pilot has an near midair collision in the pattern at bvs.

Attributes
ACN	723319
Time
Date	200701
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : bvs.airport
State Reference	WA
Altitude	msl single value : 1100
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	general aviation : personal
Make Model Name	PA-28 Cherokee/Archer II/Dakota/Pillan/Warrior
Operating Under FAR Part	Part 91
Flight Phase	descent : approach
Route In Use	approach : traffic pattern
Flight Plan	None
Aircraft 2
Make Model Name	Cessna Aircraft Undifferentiated or Other Model
Operating Under FAR Part	Part 91
Flight Phase	descent : approach
Route In Use	approach : traffic pattern
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : private
Experience	flight time last 90 days : 25 flight time total : 378 flight time type : 378
ASRS Report	723319
Person 2
Function	flight crew : single pilot
Events
Anomaly	conflict : nmac other spatial deviation
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action
Miss Distance	horizontal : 0 vertical : 100
Supplementary
Problem Areas	Airport Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

I was #3 on left downwind; runway 28 at bvs; about 3000 ft behind the cessna in question. The cessna was following aircraft #1 who was executing a base to final turn for a landing on runway 28. Due to a right crosswind; the cessna's track drifted closer and closer to the extended runway centerline drastically reducing the length of the left base leg. Once the pilot of the cessna realized this; he began to execute a right 270 degrees to the extended downwind in order to provide himself enough spacing for a left base leg. As I was following the cessna on the downwind; I was expecting him to turn toward final with an abbreviated or no left base leg. I was not at all prepared to handle this unexpected maneuver and about 3 seconds elapsed before I reacted. I attempted to radio the cessna to warn him of my position on the downwind. However; I was not able to complete the radio call as I had to react immediately by going full throttle and executing an immediate left climbing turn in order to avoid the collision. It appeared that the cessna was not aware that I was behind him until he saw me pass over him; clearing him by only 100 ft.

Original NASA ASRS Text

Title: PIPER 140 PLT HAS AN NMAC IN THE PATTERN AT BVS.

Narrative: I WAS #3 ON L DOWNWIND; RWY 28 AT BVS; ABOUT 3000 FT BEHIND THE CESSNA IN QUESTION. THE CESSNA WAS FOLLOWING ACFT #1 WHO WAS EXECUTING A BASE TO FINAL TURN FOR A LNDG ON RWY 28. DUE TO A R XWIND; THE CESSNA'S TRACK DRIFTED CLOSER AND CLOSER TO THE EXTENDED RWY CTRLINE DRASTICALLY REDUCING THE LENGTH OF THE L BASE LEG. ONCE THE PLT OF THE CESSNA REALIZED THIS; HE BEGAN TO EXECUTE A R 270 DEGS TO THE EXTENDED DOWNWIND IN ORDER TO PROVIDE HIMSELF ENOUGH SPACING FOR A L BASE LEG. AS I WAS FOLLOWING THE CESSNA ON THE DOWNWIND; I WAS EXPECTING HIM TO TURN TOWARD FINAL WITH AN ABBREVIATED OR NO L BASE LEG. I WAS NOT AT ALL PREPARED TO HANDLE THIS UNEXPECTED MANEUVER AND ABOUT 3 SECONDS ELAPSED BEFORE I REACTED. I ATTEMPTED TO RADIO THE CESSNA TO WARN HIM OF MY POS ON THE DOWNWIND. HOWEVER; I WAS NOT ABLE TO COMPLETE THE RADIO CALL AS I HAD TO REACT IMMEDIATELY BY GOING FULL THROTTLE AND EXECUTING AN IMMEDIATE L CLBING TURN IN ORDER TO AVOID THE COLLISION. IT APPEARED THAT THE CESSNA WAS NOT AWARE THAT I WAS BEHIND HIM UNTIL HE SAW ME PASS OVER HIM; CLRING HIM BY ONLY 100 FT.

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.