Narrative:

Location of incident and altitude: ZZZ airport; in the traffic pattern on the early base leg to runway xx; turning from downwind to base (left traffic). Altitude 3;300 mslidentification information:-reporting aircraft / pilot - high wing aircraft- local / flight training (traffic pattern at ZZZ)- other aircraft- low wing aircraftthe flight was a local flight; remaining exclusively in the ZZZ traffic pattern for runway xx; conducted under VFR. The altimeter setting was copied and input from the AWOS-3 at ZZZ prior to departure; which was a setting of 29.74 (both altimeters in the aircraft were adjusted to this local pressure setting. The altimeters were confirmed to be reporting within 20 feet of the published field elevation of 2;537 MSL)the local weather was visual meteorological conditions with the AWOS at ZZZ reporting calm wind; visibility greater than 10 miles; sky clear below 12;000 MSL; and the previously recorded altimeter setting of 29.74. Although I do not have the temperature / dew point recorded here; the temperature was moderate and warming and the dew point spread suggested that clouds would not be forming at low altitudes during the flight. During the flight; the air was very calm and smooth and visibility remained excellent throughout. The reporting aircraft had been conducting traffic pattern operations for a period of time (approximately 45 minutes); making multiple touch and go's. The altitude did not exceed more than 3;700 MSL and was typically at or below 3;537 MSL as the student was practicing normal approaches to landing and pattern work. On this particular circuit; nothing was noted as unusual. The student positioned the aircraft appropriately on the crosswind and downwind legs; making standard position reports and scanning for traffic in all phases. The altitude on downwind was pattern altitude (3;537 MSL). The downwind heading while making left traffic for runway xx was 290 degrees. Upon reaching a position abeam the end of the departure end of runway xx; power was set to allow a decrease in airspeed and to establish a standard descent rate of 500 feet per minute. After reaching an altitude of approximately 3;300 MSL; the student made a standard left base traffic report and initiated the descending base turn. Upon rolling out on the base turn; the other incident aircraft was observed in the downwind leg of the traffic pattern approximately 100 feet higher than the reporting plane; and no more than 300 feet laterally (moving left to right of the position of the reporting plane). As the aircraft moved left to right; in a downwind direction (extending to the west); my student exclaimed; 'should he be there?' no evasive action was taken; principally because there was no time. The proximity of the aircraft and the direction of flight resulted in the other aircraft moving from left to right and above us before a response maneuver could be made. Following this; I called on the radio; 'did you see that aircraft pass below you?' the pilot answered; 'yes.' at the closest point; I would estimate that the aircraft was less than 100 feet in front of our position and 150 feet above our position (we were descending; so this is assumed - but as it happened quickly; it would be difficult to make an accurate assessment). As mentioned in the summaries previously; the flight we were conducting was a local training flight; remaining exclusively in the traffic pattern. There was a reasonably heavy volume of traffic; with several aircraft operating in the traffic pattern and also transiting the area at or near pattern altitudes. This extended to aircraft on the RNAV-B approach toward runway yy at ZZZ (opposite of traffic) and passing overhead on the RNAV-30 approach toward runway xy at ZZZ1 airport (ZZZ1). Additionally; there were aircraft arriving from the practice areas and from north of the airport. In short; it was busy. In the aircraft; we were using an ads-B 'in' device (stratus-3) that was feeding ads-B data to my apple ipad on foreflight. I was able to monitor traffic in the vicinity and in the traffic pattern with these tools; however I also observed that there were aircraft in the area that were not being received by my ads-B device. I do not recall seeing this aircraft / registration number on my display before; during; or after the incident - but I cannot say with certainty that the other aircraft was not broadcasting on ads-B. They may have been and simply not detected. That being said; because I am aware that many aircraft in the local area are not broadcasting ads-B; it is only used as a backup to visual scanning and I do not rely on it for a complete picture of traffic or potential conflicts. On this particular circuit in the pattern; nothing was noted amiss. My student made normal traffic calls in the upwind; crosswind; and turning downwind and we did not observe any traffic conflicts in the turn to crosswind or downwind. We also did not hear any other aircraft announce an entry into the downwind at that time. However; we had noted that several aircraft during the morning's flight had made standard entries (overhead midfield and 45 degree entries) to the left traffic pattern for runway xx; and several had made non-standard entries to a busy pattern. I discussed this with my student during our circuits; as many of the entries seemed unsafe to me. These included:- announcements of 45 degree entries to left traffic for runway xx; but when the aircraft was observed it was on a 45 degree entry to right traffic for runway yy. The plane subsequently turned away and around to line up on downwind for runway xx without incident.- an aircraft that was making a straight-in approach to runway xx while traffic was on left base for runway xx. When asked on the radio; the pilot confirmed he was landing on runway xx and then was advised he had cut off an aircraft on base. After this; the pilot announced a 'mid-field entry for runway xx.'- another aircraft made a standard midfield entry for runway xx; but directly at pattern altitude with more than one aircraft in the downwind. This aircraft extended its midfield entry and executed a tear drop turn back to the downwind for runway xx. This information is included here to highlight that the pattern was busy with a lot of standard and non-standard traffic behavior; requiring a significant amount of attention to be devoted to keeping track of the traffic situation at all times. On the downwind leg; we did not see the aircraft nor did we hear any conflicting radio calls that would have made us aware that there was another aircraft behind and above our position on the downwind. As we were in a high-wing aircraft and the other aircraft was a low-wing; it is conceivable that the other pilot did not see us either; although I have some reason to believe that is unlikely. Moreover; I can assume that our radio calls and position reports would have been received; as we had talked with other aircraft that morning without difficulty. Had the aircraft been at the same altitude as we were on downwind; the proximity and position would have made it appear that he was flying in close formation and our airplane would have been strikingly obvious; but above and behind us would have made it possible to overlook. From a low wing aircraft; I still believe it would have been possible; since our position could only have been ahead and slightly below to the right. The reason I believe that the low wing aircraft was behind and above us on the downwind leg is that when we turned from downwind to base; he was moving from our left to our right and was above us. There are two possible explanations for this; in my opinion:1. When we turned crosswind; the other incident aircraft was approaching the airport on a strict downwind entry (not a 45 degree entry to the downwind) and we did not see or hear him; resulting in our turning onto the downwind in front of the aircraft. While I think this is a possibility and should be considered; I think it is unlikely. We were vigilant in scanning and making radio calls and we neither saw another aircraft at that time nor heard any radio call before or after our entry to downwind that would suggest a traffic conflict at that point. 2. After we were established on downwind; the other incident aircraft entered the traffic pattern close behind us either from the 45 degree or midfield positions and did not immediately observe another aircraft in the downwind leg. As stated previously; once we were abeam the departure end of runway xx (abeam 'the numbers') my student reduced power and initiated a 500 FPM descent per our procedure. Once we had descended approximately 200 - 300 feet; she initiated the left base turn and made a standard radio call. As she completed her turn onto the base leg; the other incident aircraft was immediately to our left and above us. Because we were able to turn 90 degrees from the downwind leg; I concluded that we had to have been ahead of the other incident aircraft in the downwind; but it would have been very close. We did not take any evasive action due to the suddenness and lack of time; but it would not have been required either. While the two aircraft were close; they were not going to collide at that point. However; in more than xx years of flying; it is the absolute closest I have been to another aircraft without flying a pre-briefed formation flight.

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Original NASA ASRS Text

Title: Instructor Pilot reported an NMAC in the pattern.

Narrative: Location of Incident and Altitude: ZZZ Airport; In the traffic pattern on the early base leg to Runway XX; turning from Downwind to Base (left traffic). Altitude 3;300 MSLIdentification Information:-Reporting Aircraft / Pilot - High wing aircraft- Local / Flight Training (Traffic Pattern at ZZZ)- Other Aircraft- low wing aircraftThe flight was a local flight; remaining exclusively in the ZZZ traffic pattern for Runway XX; conducted under VFR. The altimeter setting was copied and input from the AWOS-3 at ZZZ prior to departure; which was a setting of 29.74 (both altimeters in the aircraft were adjusted to this local pressure setting. The altimeters were confirmed to be reporting within 20 feet of the published field elevation of 2;537 MSL)The local weather was visual meteorological conditions with the AWOS at ZZZ reporting calm wind; visibility greater than 10 miles; sky clear below 12;000 MSL; and the previously recorded altimeter setting of 29.74. Although I do not have the temperature / dew point recorded here; the temperature was moderate and warming and the dew point spread suggested that clouds would not be forming at low altitudes during the flight. During the flight; the air was very calm and smooth and visibility remained excellent throughout. The reporting aircraft had been conducting traffic pattern operations for a period of time (approximately 45 minutes); making multiple touch and go's. The altitude did not exceed more than 3;700 MSL and was typically at or below 3;537 MSL as the student was practicing normal approaches to landing and pattern work. On this particular circuit; nothing was noted as unusual. The student positioned the aircraft appropriately on the crosswind and downwind legs; making standard position reports and scanning for traffic in all phases. The altitude on downwind was pattern altitude (3;537 MSL). The downwind heading while making left traffic for Runway XX was 290 degrees. Upon reaching a position abeam the end of the departure end of Runway XX; power was set to allow a decrease in airspeed and to establish a standard descent rate of 500 Feet per Minute. After reaching an altitude of approximately 3;300 MSL; the student made a standard left base traffic report and initiated the descending base turn. Upon rolling out on the base turn; the other incident aircraft was observed in the downwind leg of the traffic pattern approximately 100 feet higher than the reporting plane; and no more than 300 feet laterally (moving left to right of the position of the reporting plane). As the aircraft moved left to right; in a downwind direction (extending to the west); my student exclaimed; 'Should he be there?' No evasive action was taken; principally because there was no time. The proximity of the aircraft and the direction of flight resulted in the other aircraft moving from left to right and above us before a response maneuver could be made. Following this; I called on the radio; 'Did you see that aircraft pass below you?' the pilot answered; 'Yes.' At the closest point; I would estimate that the aircraft was less than 100 feet in front of our position and 150 feet above our position (we were descending; so this is assumed - but as it happened quickly; it would be difficult to make an accurate assessment). As mentioned in the summaries previously; the flight we were conducting was a local training flight; remaining exclusively in the traffic pattern. There was a reasonably heavy volume of traffic; with several aircraft operating in the traffic pattern and also transiting the area at or near pattern altitudes. This extended to aircraft on the RNAV-B approach toward Runway YY at ZZZ (opposite of traffic) and passing overhead on the RNAV-30 approach toward runway XY at ZZZ1 airport (ZZZ1). Additionally; there were aircraft arriving from the practice areas and from north of the airport. In short; it was busy. In the aircraft; we were using an ADS-B 'IN' device (STRATUS-3) that was feeding ADS-B data to my Apple iPad on Foreflight. I was able to monitor traffic in the vicinity and in the traffic pattern with these tools; however I also observed that there were aircraft in the area that were not being received by my ADS-B device. I do not recall seeing this aircraft / registration number on my display before; during; or after the incident - but I cannot say with certainty that the other aircraft was not broadcasting on ADS-B. They may have been and simply not detected. That being said; because I am aware that many aircraft in the local area are not broadcasting ADS-B; it is only used as a backup to visual scanning and I do not rely on it for a complete picture of traffic or potential conflicts. On this particular circuit in the pattern; nothing was noted amiss. My student made normal traffic calls in the upwind; crosswind; and turning downwind and we did not observe any traffic conflicts in the turn to crosswind or downwind. We also did not hear any other aircraft announce an entry into the downwind at that time. However; we had noted that several aircraft during the morning's flight had made standard entries (overhead midfield and 45 degree entries) to the left traffic pattern for Runway XX; and several had made non-standard entries to a busy pattern. I discussed this with my student during our circuits; as many of the entries seemed unsafe to me. These included:- Announcements of 45 degree entries to left traffic for Runway XX; but when the aircraft was observed it was on a 45 degree entry to right traffic for Runway YY. The plane subsequently turned away and around to line up on downwind for Runway XX without incident.- An aircraft that was making a straight-in approach to Runway XX while traffic was on left base for Runway XX. When asked on the radio; the pilot confirmed he was landing on Runway XX and then was advised he had cut off an aircraft on base. After this; the pilot announced a 'mid-field entry for Runway XX.'- Another aircraft made a standard midfield entry for Runway XX; but directly at pattern altitude with more than one aircraft in the downwind. This aircraft extended its midfield entry and executed a tear drop turn back to the downwind for Runway XX. This information is included here to highlight that the pattern was busy with a lot of standard and non-standard traffic behavior; requiring a significant amount of attention to be devoted to keeping track of the traffic situation at all times. On the downwind leg; we did not see the aircraft nor did we hear any conflicting radio calls that would have made us aware that there was another aircraft behind and above our position on the downwind. As we were in a high-wing aircraft and the other aircraft was a low-wing; it is conceivable that the other pilot did not see us either; although I have some reason to believe that is unlikely. Moreover; I can assume that our radio calls and position reports would have been received; as we had talked with other aircraft that morning without difficulty. Had the aircraft been at the same altitude as we were on downwind; the proximity and position would have made it appear that he was flying in close formation and our airplane would have been strikingly obvious; but above and behind us would have made it possible to overlook. From a low wing aircraft; I still believe it would have been possible; since our position could only have been ahead and slightly below to the right. The reason I believe that the low wing aircraft was behind and above us on the downwind leg is that when we turned from downwind to base; he was moving from our left to our right and was above us. There are two possible explanations for this; in my opinion:1. When we turned crosswind; the other incident aircraft was approaching the airport on a strict downwind entry (not a 45 degree entry to the downwind) and we did not see or hear him; resulting in our turning onto the downwind in front of the aircraft. While I think this is a possibility and should be considered; I think it is unlikely. We were vigilant in scanning and making radio calls and we neither saw another aircraft at that time nor heard any radio call before or after our entry to downwind that would suggest a traffic conflict at that point. 2. After we were established on downwind; the other incident aircraft entered the traffic pattern close behind us either from the 45 degree or midfield positions and did not immediately observe another aircraft in the downwind leg. As stated previously; once we were abeam the departure end of Runway XX (abeam 'the numbers') my student reduced power and initiated a 500 FPM descent per our procedure. Once we had descended approximately 200 - 300 feet; she initiated the left base turn and made a standard radio call. As she completed her turn onto the base leg; the other incident aircraft was immediately to our left and above us. Because we were able to turn 90 degrees from the downwind leg; I concluded that we had to have been ahead of the other incident aircraft in the downwind; but it would have been very close. We did not take any evasive action due to the suddenness and lack of time; but it would not have been required either. While the two aircraft were close; they were not going to collide at that point. However; in more than XX years of flying; it is the absolute closest I have been to another aircraft without flying a pre-briefed formation flight.

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.