Date: 202201
Local time of day: 1201-1800
Location: PAO.Airport, CA
Flight conditions: VMC
Light: Daylight
Aircraft: Small Aircraft
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Other Pattern
Airspace: Class D PAO
ATC / advisory: Tower PAO
Second aircraft: Small Aircraft; Low Wing; 1 Eng; Retractable Gear
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Instrument
Human factors: Confusion; Communication Breakdown
Second reporter function: Single Pilot
Anomaly: Conflict NMAC
Detector: Person Flight Crew
When detected: In-flight
Contributing factors: Procedure; Airspace Structure
Primary problem: Airspace Structure

Narrative: I was flying in the pattern doing takeoff and landing practice. It was extremely crowded with many airplanes in the pattern. I was on the downwind getting close to turning base to Runway 31. That circuit is a right pattern. I was probably alerted by TCAS; but I looked at my display and saw an aircraft close to me and below on my left side. I looked out the window and there was another airplane passing below me from my left to my right. I then saw it about 200 or 300 ft. below me on my right side. At that moment the Tower Controller asked if I saw the airplane on my right. I responded with yes" and then I said that "I just flew over him." I then proceeded to turn base and subsequently land. At that time; I was surprised that the controller didn't warn me about the airplane; but I continued my day without thinking much about it.This evening I was reflecting on what happened and realized that the incident could have been my fault. I don't recall the Tower saying to follow another airplane before landing. If so; then I should have kept that airplane in sight. As I am thinking now; if that was the case; maybe the other airplane was in the downwind leg as normal or possibly rather wide. Then; maybe I continued in the downwind pattern moving closer to the runway than the other airplane; which would put me to the right of it. It then turned to base and passed below me. By the time I saw it; it was too close for me to take any evasive action; even if I thought it was necessary.It may have been lucky that I was about 250 ft. above the published pattern altitude and the other airplane was either at pattern altitude or lower; giving us a wide margin. Had that not been the case it could have been a near miss or worse."


Second narrative: I was flying in the pattern at PAO after 1 month of not flying due to maintenance. I was on right traffic for Runway 31; and was following faster traffic. After an extended downwind; I turned base abeam the traffic and squared my turn for separation. I overshot centerline by about 1000 ft. - measured post-flight in flightradar24. I received a traffic alert and immediately saw traffic on the left downwind; slightly high. I increased my rate of turn and pitched down slightly to avoid the traffic.Further investigation helped me discover that the other traffic was on a correct 0.5 NM or perhaps slightly tight 0.4 NM; left downwind. At our closest we were between 2000 - 3000 ft. vertically separated and the other traffic was 200 ft. above. It looked close in the cockpit; but perhaps not that close upon further analysis.Several factors and lessons here. This was my first flight after a month of absence due to maintenance so I was slightly rusty. There was a lot of traffic at Palo Alto; I was aware of the traffic in the right pattern but was not aware of this traffic on the left pattern. They were inbound and had called several minutes prior to the event. Me overshooting the centerline was the most dangerous - it was partially caused by the blinding setting sun; as well as my desire to increase spacing from the traffic I was following. I could have extended downwind further instead.


Synopsis: Small aircraft pilots reported receiving TCAS alerts while flying the same traffic pattern at PAO airport resulting in an NMAC.