Narrative:

We were turning crosswind when the approaching pilot made their first radio call stating they were entering left downwind for runway 28. I spotted traffic approximately 1/4 mile away; at approximately the 1 o'clock position; same altitude; appearing to enter the pattern directly [ahead] on to the left crosswind leg of the pattern. I took the flight controls from the student and initiated a descending left turn away from the traffic; requiring between 45 and 60 degrees of bank. The oncoming traffic turned to the right; entering the left downwind leg of the pattern for runway 28. The incoming traffic stated that they had us in sight; and would fall in behind us.I lost sight of the traffic after the trailing aircraft crossed my 5 o'clock position; and we continued to fly the pattern for a landing/touch and go. Due to the early downwind turn; we were approximately 1/4-1/3 of a mile from the runway for our downwind leg. We reduced power early to compensate for the closer-than-normal downwind leg and began our descent. At approximately 1;700 feet MSL and 1/2 mile from the runway (the numbers of the runway were approximately 45 degrees behind our left shoulder) we turned left base. Upon rolling wings level (approximately 1;500msl) I re-acquired the traffic. The traffic was a biplane with a single pilot in the rear position. Being able to discern this much detail; I estimate our horizontal distance to be approximately 1;000 feet; with a vertical separation of approximately 100-200 feet higher than us; and continuing to descend.at this point we slowed down our approach and began s-turns to lengthen our final approach/increase separation. To our right; approximately 1-2 miles north of the field was a helicopter on CTAF stating they were at 1;500 MSL. I was not able to visually acquire this traffic.the biplane (conflicting traffic) then began a steep left turn directly over the approach end of runway 28 and proceeded to do a 360. His estimated altitude was between 500 and 1;000 AGL; best guess being around 700 AGL. Due to his location; I was unable to do a go-around if needed; turn right (unseen helicopter traffic that I knew was close); and couldn't turn south (left) because he was occupying that position and that would put us directly head-on to potential conflicting downwind traffic. I radioed the traffic overhead to state their intentions; and the pilot stated that he was circling the windsock. I made a judgment call that the one direction that he would not turn would be directly down; and he did not appear to be descending at that time. I took the flight controls from the student and descended to a reasonably safe vertical separation; which left us unusually low for our approach (both VASI lights were red). We proceeded to do a full stop landing and exited the runway on the first available taxiway and waited for the traffic overhead circling to land.

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Original NASA ASRS Text

Title: C172 Instructor Pilot descended below normal approach altitude at a non-towered airport due to conflict with a biplane and a helicopter while maneuvering for landing.

Narrative: We were turning crosswind when the approaching pilot made their first radio call stating they were entering left downwind for Runway 28. I spotted traffic approximately 1/4 mile away; at approximately the 1 o'clock position; same altitude; appearing to enter the pattern directly [ahead] on to the left crosswind leg of the pattern. I took the flight controls from the student and initiated a descending left turn away from the traffic; requiring between 45 and 60 degrees of bank. The oncoming traffic turned to the right; entering the left downwind leg of the pattern for Runway 28. The incoming traffic stated that they had us in sight; and would fall in behind us.I lost sight of the traffic after the trailing aircraft crossed my 5 o'clock position; and we continued to fly the pattern for a landing/touch and go. Due to the early downwind turn; we were approximately 1/4-1/3 of a mile from the runway for our downwind leg. We reduced power early to compensate for the closer-than-normal downwind leg and began our descent. At approximately 1;700 feet MSL and 1/2 mile from the runway (the numbers of the runway were approximately 45 degrees behind our left shoulder) we turned left base. Upon rolling wings level (approximately 1;500msl) I re-acquired the traffic. The traffic was a biplane with a single pilot in the rear position. Being able to discern this much detail; I estimate our horizontal distance to be approximately 1;000 feet; with a vertical separation of approximately 100-200 feet higher than us; and continuing to descend.At this point we slowed down our approach and began S-turns to lengthen our final approach/increase separation. To our right; approximately 1-2 miles north of the field was a helicopter on CTAF stating they were at 1;500 MSL. I was not able to visually acquire this traffic.The biplane (conflicting traffic) then began a steep left turn directly over the approach end of Runway 28 and proceeded to do a 360. His estimated altitude was between 500 and 1;000 AGL; best guess being around 700 AGL. Due to his location; I was unable to do a go-around if needed; turn right (unseen helicopter traffic that I knew was close); and couldn't turn south (left) because he was occupying that position and that would put us directly head-on to potential conflicting downwind traffic. I radioed the traffic overhead to state their intentions; and the pilot stated that he was circling the windsock. I made a judgment call that the one direction that he would not turn would be directly down; and he did not appear to be descending at that time. I took the flight controls from the student and descended to a reasonably safe vertical separation; which left us unusually low for our approach (both VASI lights were red). We proceeded to do a full stop landing and exited the runway on the first available taxiway and waited for the traffic overhead circling to land.

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.