Narrative:

This was an IFR training flight. VFR flight squawking 1200. We had no contact with ATC. We were tuned to the ZZZ CTAF frequency. There appeared to be a lot of 'chatter' on the frequency - most of it was related to a variety of training flights. My student has approximately 300 hrs total time. This was his second IFR training flight of the day after refueling at ZZZ. I gave my student the following scenario: transfer aircraft from ZZZ to ZZZ1 back from the maintenance on an IFR plan flight. I asked the student to do a takeoff in simulated 0/0 conditions. Acting as the 'ATC' I gave the student vectors towards zzzzz (the initial approach fix on RNAV (GPS) runway xx @ ZZZ1). The student was flying 'under the hood' with the use of 'foggles' in simulated IFR conditions. The student leveled off at 3;000 feet MSL and was flying the heading of about 260 on a vector towards zzzzz intersection. I was guiding the student through the proper sequence of IFR procedures. The student was completing the cruise checklist and I was guiding him through the proper leaning procedures. Suddenly; the garmin G430 waas ads-B alert flared up with multiple targets - these were hard to discern on a small screen in the expedited manner). Just a moment later; with my peripheral vision; I noticed an aircraft (a C172) on the 8 o'clock position to the left of our position; at the same altitude. The view to the left was blocked by the student; so the appearance of the aircraft was sudden and almost surreal. It was rapidly moving through 9 to 10 o'clock position in a very steep bank to the left. The distance between our aircraft was less than 200 feet and probably just over 100 feet. The aircraft on the; now; 10 o'clock position was rapidly descending (more than 1;000 ft/min) banking steeply to the left. All this happened so quickly that I had no chance to take an evasive action. The offending aircraft was approaching from behind and to the left of our flight path. We had the right of way and my visibility to the right was obscured by the student pilot. We continued our flight as pre-planned. Live another day.airspace to the north of ZZZ1 is incredibly busy with uncoordinated training activities. [Company]; a flight school at ZZZ1 is incredibly busy. Their instructors tend to be low total time and their attitude is that they 'own the sky and the airport.' they are a continual source of frustration for many pilots operating from ZZZ1 and I am actually quite shocked that we did not have a mid-air incident in the vicinity of ZZZ1. What prevented the disaster today was the fact the offending pilot; who did not have the right of way; saw and avoided traffic at the very last moment. This incident illustrates the limitations of ads-B. The ads-B displays can be cluttered and confusing when many targets are present and when the scale is not properly set. More important the timely information is not always available. There is no substitute for 'see and avoid' sometimes ads-B calls for traffic proximity when in fact it just projects itself. This desensitizes pilots to sudden; unexpected traffic warnings which also might have been the case today.

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Original NASA ASRS Text

Title: C-182 Flight Instructor reported a sudden NMAC event during a training flight in which the offending aircraft approached from behind maneuvered to avoid a collision. Instructor provided useful ADS-B information.

Narrative: This was an IFR training flight. VFR flight squawking 1200. We had no contact with ATC. We were tuned to the ZZZ CTAF frequency. There appeared to be a lot of 'chatter' on the frequency - most of it was related to a variety of training flights. My student has approximately 300 hrs total time. This was his second IFR training flight of the day after refueling at ZZZ. I gave my student the following scenario: transfer aircraft from ZZZ to ZZZ1 back from the maintenance on an IFR plan flight. I asked the student to do a takeoff in simulated 0/0 conditions. Acting as the 'ATC' I gave the student vectors towards ZZZZZ (the initial approach fix on RNAV (GPS) RWY XX @ ZZZ1). The student was flying 'under the hood' with the use of 'foggles' in simulated IFR conditions. The student leveled off at 3;000 feet MSL and was flying the heading of about 260 on a vector towards ZZZZZ intersection. I was guiding the student through the proper sequence of IFR procedures. The student was completing the cruise checklist and I was guiding him through the proper leaning procedures. Suddenly; the Garmin G430 WAAS ADS-B alert flared up with multiple targets - these were hard to discern on a small screen in the expedited manner). Just a moment later; with my peripheral vision; I noticed an aircraft (a C172) on the 8 o'clock position to the left of our position; at the same altitude. The view to the left was blocked by the student; so the appearance of the aircraft was sudden and almost surreal. It was rapidly moving through 9 to 10 o'clock position in a very steep bank to the left. The distance between our aircraft was less than 200 feet and probably just over 100 feet. The aircraft on the; now; 10 o'clock position was rapidly descending (more than 1;000 ft/min) banking steeply to the left. All this happened so quickly that I had no chance to take an evasive action. The offending aircraft was approaching from behind and to the left of our flight path. We had the right of way and my visibility to the right was obscured by the student pilot. We continued our flight as pre-planned. Live another day.Airspace to the north of ZZZ1 is incredibly busy with uncoordinated training activities. [Company]; a flight school at ZZZ1 is incredibly busy. Their instructors tend to be low total time and their attitude is that they 'own the sky and the airport.' They are a continual source of frustration for many pilots operating from ZZZ1 and I am actually quite shocked that we did not have a mid-air incident in the vicinity of ZZZ1. What prevented the disaster today was the fact the offending pilot; who did not have the right of way; saw and avoided traffic at the very last moment. This incident illustrates the limitations of ADS-B. The ADS-B displays can be cluttered and confusing when many targets are present and when the scale is not properly set. More important the timely information is not always available. There is no substitute for 'see and avoid' Sometimes ADS-B calls for traffic proximity when in fact it just projects itself. This desensitizes pilots to sudden; unexpected traffic warnings which also might have been the case today.

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.