Date: 201812
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Amateur/Home Built/Experimental
Operator: Personal
Mission: Personal
Flight phase: Final Approach
Airspace: Class E ZZZ
ATC / advisory: UNICOM ZZZ
Second aircraft: Any Unknown or Unlisted Aircraft Manufacturer
Reporter organization: Personal
Reporter function: Single Pilot
Reporter qualification: Flight Crew Private
Human factors: Time Pressure; Communication Breakdown; Situational Awareness
Anomaly: Conflict NMAC; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Contributing factors: Human Factors; Procedure; Airspace Structure
Primary problem: Human Factors

Narrative: Weather was VFR. While approaching the uncontrolled field; I heard two aircraft report inbound. There was also an aircraft on a practice instrument approach and an airplane or two in the pattern. It was unusually busy for this small airport. The airport has one runway. Planes were landing on 17. I turned on the strobes and landing light; reported inbound 4 miles out; reported crosswind; and made a third radio call on downwind.While on downwind at midfield the other plane came out of the west and crossed over midfield below pattern altitude heading 050. I saw the low wing Piper at my 10 o'clock. It flew almost directly under me. I estimate it was 200 feet below. I lost sight of it for a few tense seconds as it went under the cowl. For evasive action; I didn't want to break left into landing traffic; or right in his direction or up thinking he may have climbed to pattern and I could now be under him and in a high wing; not see him. I climbed 50 feet. The plane reappeared at my 2 o'clock and turned downwind in front of me. I radioed 'Someone just flew under me.' I was now number four to land.Afterwards; the other pilot said he thought I was further away when he crossed the field and turned downwind. He didn't see me I suspect because he was looking forward and left in anticipation of turning downwind while the converging angle was to his right. He said he was 100 feet or so below pattern altitude. I was right at pattern altitude. I estimate we were 200 feet apart.Recommendations:Pilots should be taught that flying over midfield at pattern altitude and then turning downwind is an approach that carries high risk. It should be seldom used and never when there are other aircraft in the vicinity. Even when there appears to be no traffic; there may be unseen planes in the pattern; radio calls stepped on and pilots on the wrong frequency. Safe practice is to cross the field well above pattern altitude and then fly a standard pattern or fly crosswind to a standard pattern at public airports.Crossing over the airport at 500 feet above pattern should be changed to 800 feet because other planes may be well above pattern altitude. Planes sometimes begin their descent late and descend in the pattern. Aircraft also sometimes exceed pattern when climbing after takeoff and turning downwind.




Synopsis: GA pilot reported an NMAC while operating in the pattern at a non-towered airport.