Skyhawk 172/Cutlass 172
Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Instrument
Flight Crew Last 90 Days 50; Flight Crew Total 900; Flight Crew Type 650
Communication Breakdown
Conflict Airborne Conflict
Flight Crew Took Evasive Action
Human Factors; Procedure
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.
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.