SR20
Flight Crew Instrument; Flight Crew Commercial; Flight Crew Flight Instructor
Flight Crew Last 90 Days 50; Flight Crew Total 1300; Flight Crew Type 1200
Situational Awareness
ATC Issue All Types; Aircraft Equipment Problem Less Severe; Conflict NMAC; Deviation - Altitude Excursion From Assigned Altitude
Air Traffic Control Provided Assistance; Flight Crew Took Evasive Action
Human Factors; Aircraft
My student was flying the VOR 35 into ZZZ Airport and was issued the published missed at ZZZZ Intersection but was asked to hold at 3;600 instead of the published 2;600 feet. On our second trip around on the outbound leg our TCAS issued a traffic alert with no altitude indication heading across our present course. As we were in a low wing aircraft I took controls and issued a climb to hopefully avoid the inbound aircraft. After climbing to 3;800 feet I was able to spot a Piper single engine aircraft that was crossing right underneath us. At that time I informed ZZZ departure of why we were higher than we were supposed to be and made them aware of the piper flying without a mode-c transponder. ZZZ Departure later reported back that the piper had called up ZZZ1 Tower and confirmed that their mode-c was not working.
A pilot and instructor experienced an automated traffic alert and near mid air collision when they encountered a conflicting aircraft with an inoperative transponder. ATC had not provided any traffic information.