Skyhawk 172/Cutlass 172
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Flight Instructor; Flight Crew Commercial
Flight Crew Last 90 Days 200; Flight Crew Total 730; Flight Crew Type 25
Distraction; Confusion
Aircraft Equipment Problem Critical
Flight Crew Diverted; Flight Crew Landed in Emergency Condition; Flight Crew Requested ATC Assistance / Clarification; General Declared Emergency; General Maintenance Action
Aircraft; Human Factors
I was approached by the Owner of the company and the Mechanic about taking a C-172RG out on a 30 minute flight to check the electrical system. I had flown the aircraft the day before and had no significant issues on the 1.2 hour flight. Earlier in the morning on a lesson with another instructor the aircraft had returned due to some of the circuit breakers popping. The Mechanic was notified and I saw him doing a static run-up with the company Owner on the ramp as I pulled in from my training flight. Everything sounded normal and the engine started normally. The Mechanic explained that he could see no major abnormalities with any of the circuit breakers. Since the landing gear breaker was one of the breakers that popped; [the Mechanic] and the Owner wanted take the plane up for a quick flight to recycle the gear a couple of times and make sure there was no issue.We went out to the plane; pushed it out and I did a thorough preflight/walkaround. We got in the aircraft and the engine started normally. We then taxied out and did a full run-up and it all passed. The Mechanic was at the controls for the takeoff as I monitored. The takeoff itself; for lack of a better term; felt different. We climbed out a little slower than usual. The aircraft's engine sounded normal and we were able to get the gear up and [achieved the] 25' MAP/2500RPM setting that we were used to for climbout. The airspeeds did seem lower than usual during the climbout. By the time we leveled off at around 1;200 feet; we gained a lot of airspeed back but; at the same time;  we were only getting 80-90K instead of the close to 100K that I'm used to on that aircraft at a cruise. I took the controls then; since the numbers and the settings didn't seem right. I wanted to head back to the airport. [The Mechanic] agreed with my decision and I told TRACON we were returning and wanted to switch to ZZZ Tower. They approved it as requested. It was only after the 180 degree turn and frequency switch that the engine started to under perform. It didn't sound or feel as if it was surging at the time but it was making the flight controls feel heavier than usual. Tower asked if we needed assistance but since we were still getting enough power to maintain flight; I declined it; at first. Almost right after I said that; the surges began. I began with carb heat and that didn't work. The power continued to surge and drop but it was getting weaker and weaker overall. I declared an emergency with the intent of heading straight for the runway. That didn't work. As I looked around; there was a small local field; unplowed; with trees surrounding it; but it would have required another 180 degree turn at less than 1;000 feet. I then asked for ZZZ2 Runway XX; since it was a straight shot and I also fly out of there regularly and am familiar with the airport. I decided to have that as my primary alternate but shadowed a highway below us as a back up. Once I had selected the airfield; we continued to lose altitude; I went through the engine failure flow from memory as best as possible. I did not have time to verify with the checklist.I looked at the Mechanic and asked; 'What am I missing and what's wrong?' The engine instruments were in the green and he noted that the carburetor temperature indicator was fine. I kept my eyes on potential landing points and the airspeed indicator and realized that we weren't going to make it to ZZZ2 or ZZZ or any other airfield. I looked down the highway and paid attention to stoplights and road lights. I believe I also told Tower I was going down on the highway. Everything after the 180 degree turn back to ZZZ happened so fast I don't recall exactly what in order it happened. I told the Mechanic to brace; found a break in traffic; lowered the gear; landed on the median; and fortunately avoided impacting any structures on the way down including anybody or anything. Right away; I shut down the aircraft. All on board were unharmed and exited.Police; firefighters; and EMTs arrived very quickly.
On a maintenance test flight the engine of the C-172RG began to lose power and the pilot and Mechanic on board were unable to make it to an airport/runway.  They landed on a highway median with no injuries or damage other than to the airplane.