Narrative:

While I was on a training flight with a student; my friend (in another aircraft) and I were making radio calls and operating in the vicinity of each other. I made a radio call letting everyone in the area know I was returning to ZZZ with my student.my friend asked; 'would you like some company?' I ignorantly responded; 'sure!' we maintained straight and level while he pulled up along my right wing. I estimate his prop actually was within 5 ft. Of my wingtip. Realizing a potential collision hazard; I began a turn to the left and deviated away. He initially followed and then broke off. We returned separately to ZZZ. I did not conduct a briefing with my friend before-hand; nor have I ever flown in formation. I was not expecting him to fly as close as he did; which was certainly an assumption on my part. Because this was a training flight with a new private pilot student who had not flown in 15 years; and formation flight was not at all the intention of my flight with my student today. I felt that I let my responsibilities as a CFI be out shadowed by the excitement of formation flight. My student enjoyed the view; but I debriefed with him on the ground that what we did was not okay. Additionally; I'm not sure if flying with a student where formation flight is not part of the plan for that day constitutes 'carrying passengers for hire.' especially considering how malleable students are to the law of primacy; I did not want him to believe this was acceptable. This was a horrible situation that I allowed myself to get into and I never want to experience it again. Formation flying is an amazing privilege we have in aviation; but needs to be respected with sincerity and safety.

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Original NASA ASRS Text

Title: Flight instructor reported excessive closure with other aircraft during formation flight.

Narrative: While I was on a training flight with a student; my friend (in another aircraft) and I were making radio calls and operating in the vicinity of each other. I made a radio call letting everyone in the area know I was returning to ZZZ with my student.My friend asked; 'Would you like some company?' I ignorantly responded; 'Sure!' We maintained straight and level while he pulled up along my right wing. I estimate his prop actually was within 5 ft. of my wingtip. Realizing a potential collision hazard; I began a turn to the left and deviated away. He initially followed and then broke off. We returned separately to ZZZ. I did not conduct a briefing with my friend before-hand; nor have I ever flown in formation. I was not expecting him to fly as close as he did; which was certainly an assumption on my part. Because this was a training flight with a new private pilot student who had not flown in 15 years; and formation flight was not at all the intention of my flight with my student today. I felt that I let my responsibilities as a CFI be out shadowed by the excitement of formation flight. My student enjoyed the view; but I debriefed with him on the ground that what we did was not okay. Additionally; I'm not sure if flying with a student where formation flight is not part of the plan for that day constitutes 'carrying passengers for hire.' Especially considering how malleable students are to the law of primacy; I did not want him to believe this was acceptable. This was a horrible situation that I allowed myself to get into and I never want to experience it again. Formation flying is an amazing privilege we have in aviation; but needs to be respected with sincerity and safety.

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.