C172 pilot and a PA28 had a near midair collision in pao class D airspace.

Attributes
ACN	559155
Time
Date	200208
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : pao.airport
State Reference	CA
Altitude	msl single value : 500
Environment
Flight Conditions	VMC
Weather Elements	other
Aircraft 1
Controlling Facilities	tower : pao.tower
Operator	general aviation : personal
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	descent : approach
Route In Use	approach : traffic pattern
Flight Plan	None
Aircraft 2
Controlling Facilities	tower : pao.tower
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
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : private pilot : instrument
Experience	flight time last 90 days : 30 flight time total : 806 flight time type : 650
ASRS Report	559155
Person 2
Affiliation	other
Function	flight crew : single pilot
Events
Anomaly	conflict : nmac inflight encounter : weather inflight encounter other non adherence : required legal separation other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action
Miss Distance	horizontal : 150 vertical : 0
Supplementary
Problem Areas	FAA Flight Crew Human Performance ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	other
Situations
ATC Facility	procedure or policy : pao.tower

Narrative:

We approached pao from the salt ponds. We entered the pattern (normal right for runway 31). Eventually, on downwind, approximately abeam the runway 31 numbers, we were told by tower that we were #3 to land. The visibility was very poor, so most of my concentration was on looking for other aircraft. One aircraft on short final stated he was going around. I continued downwind because I had not seen another aircraft pass yet. Soon one did (the one I thought to be #2) and I did my turn to base. 1/2 way on my turn to final, there was a cherokee very close just behind us. We continued straight ahead and the cherokee did a right 360 degree turn (we noticed each other at the same time). The cherokee noted on the radio that he got cut off and I noted I was #3. I believe there were 2 events that caused the confusion: 1) I was counting #1, #2, #3, etc of the aircraft in the air and where they were in the pattern. In discussing it with a pilot who was on board in my aircraft, the controller probably wasn't counting the guy on short final that eventually went around. It would help if there was a uniform way to count these. 2) I should be more vigilant as to what type of aircraft is #1, #2, etc. The distraction for me was poor visibility (haze).

Original NASA ASRS Text

Title: C172 PLT AND A PA28 HAD A NMAC IN PAO CLASS D AIRSPACE.

Narrative: WE APCHED PAO FROM THE SALT PONDS. WE ENTERED THE PATTERN (NORMAL R FOR RWY 31). EVENTUALLY, ON DOWNWIND, APPROX ABEAM THE RWY 31 NUMBERS, WE WERE TOLD BY TWR THAT WE WERE #3 TO LAND. THE VISIBILITY WAS VERY POOR, SO MOST OF MY CONCENTRATION WAS ON LOOKING FOR OTHER ACFT. ONE ACFT ON SHORT FINAL STATED HE WAS GOING AROUND. I CONTINUED DOWNWIND BECAUSE I HAD NOT SEEN ANOTHER ACFT PASS YET. SOON ONE DID (THE ONE I THOUGHT TO BE #2) AND I DID MY TURN TO BASE. 1/2 WAY ON MY TURN TO FINAL, THERE WAS A CHEROKEE VERY CLOSE JUST BEHIND US. WE CONTINUED STRAIGHT AHEAD AND THE CHEROKEE DID A R 360 DEG TURN (WE NOTICED EACH OTHER AT THE SAME TIME). THE CHEROKEE NOTED ON THE RADIO THAT HE GOT CUT OFF AND I NOTED I WAS #3. I BELIEVE THERE WERE 2 EVENTS THAT CAUSED THE CONFUSION: 1) I WAS COUNTING #1, #2, #3, ETC OF THE ACFT IN THE AIR AND WHERE THEY WERE IN THE PATTERN. IN DISCUSSING IT WITH A PLT WHO WAS ON BOARD IN MY ACFT, THE CTLR PROBABLY WASN'T COUNTING THE GUY ON SHORT FINAL THAT EVENTUALLY WENT AROUND. IT WOULD HELP IF THERE WAS A UNIFORM WAY TO COUNT THESE. 2) I SHOULD BE MORE VIGILANT AS TO WHAT TYPE OF ACFT IS #1, #2, ETC. THE DISTR FOR ME WAS POOR VISIBILITY (HAZE).

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.