Narrative:

After returning to grand forks from a cross country flight; I requested a long landing to allow my student to practice a soft field landing. ATC put us on extended downwind to allow the aircraft behind us to land first; and then cleared us for 17R behind them. While on approximately a one mile final for 17R the ads-B indicated a traffic alert directly behind us; at very close proximity and at the same altitude. I initially thought this was a false return of our own aircraft. I turned around to visually verify the traffic warning and saw another C172 through the rear window that appeared very close and on glide path; which appeared to be overtaking us. Due to the close proximity of the aircraft; I took the flight controls from my student and aborted the approach by executing a climbing right turn to a heading of west. I immediately informed ATC of my deviation. Upon receiving my transmission; ATC spaced us in front of another aircraft on downwind; which in my opinion never caused any danger of an additional traffic situation; as we had the aircraft in sight shortly after the turn. ATC informed us that overtaking aircraft had been doing a low approach; which seemed to fit with what I had seen out the window. From what I recall hearing on the radio; the other aircraft (also a FBO aircraft) was doing an instrument approach to terminate in a missed approach. The other aircraft; which would have been following FBO procedures as well; would have been flying at 90 KTS on the approach; while we were on a VFR final approach at 63 KTS with full flaps. I was not able to determine if the other aircraft had us in sight; but at that moment; I felt that the other aircraft was in danger of overtaking us and colliding with our aircraft. I did not feel that there was sufficient time available to query ATC about the aircraft; so I elected to take evasive action to prevent what I thought was an imminent collision.

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Original NASA ASRS Text

Title: C172 instructor with student is advised of traffic close behind during approach by ADS-B and elects to go around. The traffic behind had been cleared for a low approach and apparently had the reporter in sight.

Narrative: After returning to Grand Forks from a cross country flight; I requested a long landing to allow my student to practice a soft field landing. ATC put us on extended downwind to allow the aircraft behind us to land first; and then cleared us for 17R behind them. While on approximately a one mile final for 17R the ADS-B indicated a traffic alert directly behind us; at very close proximity and at the same altitude. I initially thought this was a false return of our own aircraft. I turned around to visually verify the traffic warning and saw another C172 through the rear window that appeared very close and on glide path; which appeared to be overtaking us. Due to the close proximity of the aircraft; I took the flight controls from my student and aborted the approach by executing a climbing right turn to a heading of west. I immediately informed ATC of my deviation. Upon receiving my transmission; ATC spaced us in front of another aircraft on downwind; which in my opinion never caused any danger of an additional traffic situation; as we had the aircraft in sight shortly after the turn. ATC informed us that overtaking aircraft had been doing a low approach; which seemed to fit with what I had seen out the window. From what I recall hearing on the radio; the other aircraft (also a FBO aircraft) was doing an instrument approach to terminate in a missed approach. The other aircraft; which would have been following FBO procedures as well; would have been flying at 90 KTS on the approach; while we were on a VFR final approach at 63 KTS with full flaps. I was not able to determine if the other aircraft had us in sight; but at that moment; I felt that the other aircraft was in danger of overtaking us and colliding with our aircraft. I did not feel that there was sufficient time available to query ATC about the aircraft; so I elected to take evasive action to prevent what I thought was an imminent collision.

Data retrieved from NASA's ASRS site as of July 2013 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.