Pilot reported an near midair collision event with a nonreporting aircraft while in landing pattern.

Attributes
ACN	1745526
Time
Date	202006
Local Time Of Day	0601-1200
Place
Locale Reference	COI.Airport
State Reference	FL
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Small Aircraft High Wing 1 Eng Fixed Gear
Operating Under FAR Part	Part 91
Flight Phase	Takeoff
Flight Plan	None
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Flight Plan	None
Person 1
Function	Pilot Flying
Qualification	Flight Crew Commercial Flight Crew Flight Instructor Flight Crew Instrument
Experience	Flight Crew Last 90 Days 34 Flight Crew Total 357 Flight Crew Type 30
Events
Anomaly	Conflict Airborne Conflict Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Published Material / Policy
Miss Distance	Horizontal 2000

Narrative:

While (left) downwind in the pattern following other traffic in the pattern; another aircraft about 100-200 ft. Below us headed in the opposite direction flew straight at us. We initiated a climb and turned left to avoid traffic; then departed the pattern due to the event. We believe that the other aircraft might have been maneuvering to the 45 to the downwind; but being so low and flying opposite to traffic pattern (with the existing traffic already flying at altitude) was dangerous. We do not know if he was on the radios; and did not hear him radio his intentions; so there was a lack of communication. The airport is uncontrolled and people often do not use their radios; but the entry procedure of this aircraft could have caused serious issues.

Original NASA ASRS Text

Title: Pilot reported an NMAC event with a nonreporting aircraft while in landing pattern.

Narrative: While (left) downwind in the pattern following other traffic in the pattern; another aircraft about 100-200 ft. below us headed in the opposite direction flew straight at us. We initiated a climb and turned left to avoid traffic; then departed the pattern due to the event. We believe that the other aircraft might have been maneuvering to the 45 to the downwind; but being so low and flying opposite to traffic pattern (with the existing traffic already flying at altitude) was dangerous. We do not know if he was on the radios; and did not hear him radio his intentions; so there was a lack of communication. The airport is uncontrolled and people often do not use their radios; but the entry procedure of this aircraft could have caused serious issues.

Data retrieved from NASA's ASRS site 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.