Narrative:

While on a transition training flight; I was the instructor pilot; my student entered the traffic pattern at ZZZ and announced turning left downwind for runway xx. Between that radio call and his next radio call; announcing that we were turning left base; the student inadvertently pressed (and held) the flip-flop button on the stick; which switched the radio to 121.5. This is an annoying feature built into this radio (garmin). When my student announced on the radio that we were turning left base; someone notified us 'you're on guard'. Having briefed this possible situation; my student immediately flipped back to the CTAF freq. We then turned onto final for runway xx. Neither me or my student; after the fact; can remember if we made a radio call announcing our turn to final. Student proceeded to fly a good approach to a good landing and I instructed him to exit at the taxiway to our left; about 1;000 feet ahead so we could reconfigure our radio frequency. As we slowed near the taxiway; I looked to our left and was startled to see a mooney; less than 15 feet off our left wing tip; rolling along with us; as if we had just landed in formation. No surprise; he wasn't happy with us; and we weren't happy with him. Apparently he never heard us on the radio; and we never heard him. I'm a relatively high time pilot and my student has even more experience than I do; and neither of us depend on the radio for traffic avoidance. Throughout 3 hours of training on this day; we constantly reminded each other of visual call outs; clear on final before we turned. Neither of us saw the mooney; period. Neither of us feel good about that; as things turned out we both realized that we had screwed up; the mooney had to have been either in front of us (on final while we were on base) or to our right (long final; or underneath us); were not sure. However we ended up in this situation; it seems that luck is the only reason we didn't collide. During a discussion in person; on the ground; the mooney pilot was livid that we had flown right over him on final; nearly hitting him. Because neither me nor my student ever saw him; that may be true. Sometimes things just happen; even to good people doing everything right. We simply didn't see him. That was a mistake; and we own that. That said; I have never personally seen two airplanes land in formation by accident. I believe the gentleman in the mooney intentionally landed next to us and I'm not very happy about that.

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Original NASA ASRS Text

Title: Pilot reported minor radio problem which was corrected; but upon landing; they landed in formation with another aircraft unknown to the reporter.

Narrative: While on a transition training flight; I was the instructor pilot; my student entered the traffic pattern at ZZZ and announced turning left downwind for Runway XX. Between that radio call and his next radio call; announcing that we were turning left base; the student inadvertently pressed (and held) the flip-flop button on the stick; which switched the radio to 121.5. This is an annoying feature built into this radio (Garmin). When my student announced on the radio that we were turning left base; someone notified us 'You're on GUARD'. Having briefed this possible situation; my student immediately flipped back to the CTAF freq. We then turned onto final for Runway XX. Neither me or my student; after the fact; can remember if we made a radio call announcing our turn to final. Student proceeded to fly a good approach to a good landing and I instructed him to exit at the taxiway to our left; about 1;000 feet ahead so we could reconfigure our radio frequency. As we slowed near the taxiway; I looked to our left and was startled to see a MOONEY; less than 15 feet off our left wing tip; rolling along with us; as if we had just landed in formation. No surprise; he wasn't happy with us; and we weren't happy with him. Apparently he never heard us on the radio; and we never heard him. I'm a relatively high time pilot and my student has even more experience than I do; and neither of us depend on the radio for traffic avoidance. Throughout 3 hours of training on this day; we constantly reminded each other of visual call outs; clear on final before we turned. Neither of us saw the Mooney; period. Neither of us feel good about that; as things turned out we both realized that we had screwed up; the Mooney had to have been either in front of us (on final while we were on base) or to our right (long final; or underneath us); were not sure. However we ended up in this situation; it seems that luck is the only reason we didn't collide. During a discussion in person; on the ground; the Mooney pilot was livid that we had flown right over him on final; nearly hitting him. Because neither me nor my student ever saw him; that may be true. Sometimes things just happen; even to good people doing everything right. We simply didn't see him. That was a mistake; and we own that. That said; I have never personally seen two airplanes land in formation by accident. I believe the gentleman in the Mooney intentionally landed next to us and I'm not very happy about that.

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.