Narrative:

I had listened to the CTAF of a nearby airport even though I was not landing there; oddly enough to listen for traffic; and to be safe.when I returned to my home airport; I failed to hit the flip flop switch; so I was still listening and talking on the nearby airport rather than the CTAF of the actual airport I was landing at.I made my calls; though on the wrong frequency. I saw no one and flew a normal downwind; base and final.as I got close to the threshold; I observed a small aerobatic aircraft ahead of me; also landing on the same runway. I immediately did a go around and broke off to the right and climbed. As I climbed out; I looked at the radios trying to figure out if I did something wrong.it was then; on the climb out; that I spotted that I had forgotten to flip flop. I made a call stating that I would be entering the downwind and the aircraft that had landed came on stating that he was back taxiing down the landing runway. I am not sure he ever saw me.in the future; I will double and triple check that I am on the correct frequency; and I will similarly use more vigilance with my visual lookout; which is primary.I had been looking out; but somehow missed him. He was small and probably fast moving.I am a flight instructor and know that the majority of mid airs happen in exactly this scenario; but after [so many] years of flying; this is the closest I have had. My lack of checking the frequency will not happen again. As usual; there was an additional factor; as this landing was into the sun; which may have caused me difficulties in picking up the small plane ahead of me.

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Original NASA ASRS Text

Title: Small aircraft pilot reported an NMAC in the pattern at GFL non-towered field.

Narrative: I had listened to the CTAF of a nearby airport even though I was not landing there; oddly enough to listen for traffic; and to be safe.When I returned to my home airport; I failed to hit the flip flop switch; so I was still listening and talking on the nearby airport rather than the CTAF of the actual airport I was landing at.I made my calls; though on the wrong frequency. I saw no one and flew a normal downwind; base and final.As I got close to the threshold; I observed a small aerobatic aircraft ahead of me; also landing on the same runway. I immediately did a go around and broke off to the right and climbed. As I climbed out; I looked at the radios trying to figure out if I did something wrong.It was then; on the climb out; that I spotted that I had forgotten to flip flop. I made a call stating that I would be entering the downwind and the aircraft that had landed came on stating that he was back taxiing down the landing runway. I am not sure he ever saw me.In the future; I will double and triple check that I am on the correct frequency; and I will similarly use more vigilance with my visual lookout; which is primary.I had been looking out; but somehow missed him. He was small and probably fast moving.I am a flight instructor and know that the majority of mid airs happen in exactly this scenario; but after [so many] years of flying; this is the closest I have had. My lack of checking the frequency will not happen again. As usual; there was an additional factor; as this landing was into the sun; which may have caused me difficulties in picking up the small plane ahead of me.

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.