Aeronca Champion
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Multiengine
Flight Crew Last 90 Days 39; Flight Crew Total 11898; Flight Crew Type 69
Aircraft Equipment Problem Critical
Flight Crew Landed in Emergency Condition
Aircraft
7 statute miles northeast of ZZZ airport in cruise flight at 2300 MSL the engine RPM decreased rapidly from 2300 to 700 RPM. The throttle was open and the carburetor heat off. This was a training flight with an instructor and student pilot on board. At the time of the incident the student pilot was the pilot flying. I was monitoring ZZZ1 tower (14 miles to the northeast of ZZZ) frequency at the time of the uncommanded power reduction when I assumed the controls of the aircraft and called ZZZ1 tower frequency.  My intention to proceed for a straight in approach to ZZZ airport Runway XX. ZZZ1 tower acknowledged the emergency call and alerted the appropriate first responders. A helicopter in the area hearing the distress call followed our aircraft to ZZZ; however we never acquired visual contact with the helicopter. I discovered that with rapid multiple throttle movements from full open to flight idle the engine would surge to 2300 RPM and remain there for 2 to 6 seconds and return to 700 RPM. I continued the rapid throttle movements and the engine continued to surge 2300 to 700 RPM. The aircraft was able to maintain sufficient altitude to reach Runway XX at ZZZ. I was unable to switch to CTAF on the overhead radio because all of my actions were required to keep the engine surging 2300 to 700 RPM in hopes of reaching Runway XX. After landing and clearing Runway XX at ZZZ I contacted ZZZ1 tower by telephone and reported out safe landing.
Aeronca Champion instructor pilot reported the engine began surging while at cruise. They were able to make a landing at a nearby airport.