Date: 202102
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Cessna Aircraft Undifferentiated or Other Model
Operating under: Part 91
Flight plan: VFR
Mission: Training
Flight phase: Descent
Airspace: Class E ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Engine
Component problem: Malfunctioning
Reporter organization: FBO
Reporter function: Instructor
Reporter qualification: Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Instrument
Human factors: Situational Awareness; Time Pressure
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: After detailed pre-flight inspection according to manufacturer checklist; we noticed that both fuel tanks are full; samples from each fuel sump and sump under the engine are clear; we checked the color - blue color for 100LL; there was no water or other contaminants; oil level was in the operational limits for our airplane; and we decided that airplane is in the condition to make a safe flight. After listening the ATIS and getting all necessary information about the airport; we contacted Clearance Delivery requesting VFR Flight to NW (northwest) to our practice area; and after that Ground Control for taxi instruction.We completed the runup at the runup area next to Runway XX; as instructed by Ground Control; following every step on the checklist. During the runup we didn't find any issues with the airplane; magneto check was within the manufacturer limits; oil pressure and temperature were ''in green'; engine was working and responding normally like any other day. After completing runup; and agreeing that there is nothing wrong with the airplane; we decided to proceed with our flight. After contacting Tower; we departed NW to practice area. Student was flying the airplane and I was monitoring his and the airplane's performance. During takeoff roll we checked engine instruments; everything was normal; and we continued with liftoff and climb. When we arrived at [the] practice area we practiced Steep turns; S-Turns over the road; and turns around the point. During the time from takeoff; climb and during maneuvers; the engine was performing normally as well; without any issues. Once we completed the maneuvers we decided to go back to our airport. After gettingATIS information; [student] contacted the Tower and requested a full stop landing on Runway XY. We were told to proceed directly to the Airport.At that moment we were at around 1;700-1;800 feet and decided to slowly start our descent. Around 20-30 seconds after that we experienced engine roughness; loss of power and the airplane started shaking; and we started losing altitude. I took over the controls from [student] to try to troubleshoot and to find out what exactly could cause the airplane to behave like that. After checking the fuel selector (BOTH); mixture position (FULL RICH); carburetor heat (ON); primer (IN AND LOCKED) and ignition (BOTH); and noticing that everything is in position for normal operation; I started reducing the power to see how airplane will behave. With less power; shaking was reduced; but still present; and altitude losing was increased. After that I advanced power to maximum to see how the airplane will respond; but rough running increased again; shaking increased; and altitude loss was reduced but still present.At that moment we were at around 1;300-1;400 feet and descending; and I decided to contact the Tower again and to try to explain our situation. Tower asked me if we can come back; and after finding out that we are constantly descending regardless of our power setting; I acknowledge them that we are unable to do so. I decided to [follow] the [the] Expressway; to stay away from busy streets and populated areas; and to try to at least maintain the present altitude which was at that moment around 900 feet. They cleared us to land at any runway at any airport around; but not being able to maintain altitude using different power settings; I knew that we were not going to make a safe landing at any airport around; because we were getting too low; and airports were 8-10 NM far from us. At that moment we were at around 700 feet and descending; when I told the Tower that we will probably land somewhere around the Expressway. Having the populated area and narrow streets on our left side; [marsh] on our right side; and low altitude; I decided the best option will be to land on Highway; which; we were lucky; was not too busy. Having the wind from [the south] and traffic flow towards it; landing in the southbound lane was the best choice I could make at that moment. We touched down in the middle lane; and immediately started moving the airplane to the right side so traffic can keep moving. After noticing that we landed safely; without any injuries and damage to other persons and property; we secured and exited the airplane.




Synopsis: C172 instructor pilot reported a power loss resulting in a landing off airport.