Narrative:

My aircraft arrived in the airport environment and I contacted tower as instructed by ny approach control who was handling my VFR flight. The frequency was very busy with arriving IFR traffic landing and departing 34 and VFR traffic landing 29. Upon receiving instructions to fly a left pattern; I turned final to 29 and was given landing clearance which I acknowledged. About 1 mile from the runway threshold at about 500 ft AGL; a cirrus aircraft suddenly appeared at my two o'clock position and passed just below me by an estimated 20 feet. In thirty years of flying; it was the closest mid-air I have experienced. A few seconds later tower issued go-around instructions to me which I executed and landed after the second approach uneventfully. I did not speak to tower about the incident nor the pilot of the other aircraft who subsequently landed behind me and parked at the same FBO.I believe (though am not sure) that the other cirrus had been given instructions to perform a 360 for spacing and the pilot and/or tower lost situational awareness causing him to penetrate my final approach. Why he was at that low altitude; I don't know. Certainly; the traffic load on [that day] was a factor. My focus on landing and confidence in ATC providing separation at that late stage of landing was a factor. I don't think I would have seen the cirrus even if I had been looking out the right side of the aircraft. He seemed to be banked either as part of a turn or as part of an evasive maneuver. The speed with which the incident occurred was remarkable. I caught only a glimpse of the offending aircraft and had no time to evade. Fortunately; we were separated (minimally) vertically.

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Original NASA ASRS Text

Title: Cirrus SR22 Pilot reported a low-altitude NMAC with another light aircraft on short final to HPN airport.

Narrative: My aircraft arrived in the airport environment and I contacted Tower as instructed by NY approach control who was handling my VFR flight. The frequency was very busy with arriving IFR traffic landing and departing 34 and VFR traffic landing 29. Upon receiving instructions to fly a left pattern; I turned final to 29 and was given landing clearance which I acknowledged. About 1 mile from the runway threshold at about 500 ft AGL; a Cirrus aircraft suddenly appeared at my two o'clock position and passed just below me by an estimated 20 feet. In thirty years of flying; it was the closest mid-air I have experienced. A few seconds later Tower issued go-around instructions to me which I executed and landed after the second approach uneventfully. I did not speak to Tower about the incident nor the pilot of the other aircraft who subsequently landed behind me and parked at the same FBO.I believe (though am not sure) that the other Cirrus had been given instructions to perform a 360 for spacing and the pilot and/or Tower lost situational awareness causing him to penetrate my final approach. Why he was at that low altitude; I don't know. Certainly; the traffic load on [that day] was a factor. My focus on landing and confidence in ATC providing separation at that late stage of landing was a factor. I don't think I would have seen the Cirrus even if I had been looking out the right side of the aircraft. He seemed to be banked either as part of a turn or as part of an evasive maneuver. The speed with which the incident occurred was remarkable. I caught only a glimpse of the offending aircraft and had no time to evade. Fortunately; we were separated (minimally) vertically.

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.