Date: 202004
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Skyhawk 172/Cutlass 172
Operator: Personal
Operating under: Part 91
Flight plan: VFR
Mission: Training
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: CTAF ZZZ
Aircraft component: Carburetor
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Private; Flight Crew Instrument
Human factors: Troubleshooting; Workload; Time Pressure; Situational Awareness
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Aircraft Equipment Problem Dissipated; Flight Crew Took Evasive Action; Flight Crew Overcame Equipment Problem; Flight Crew Landed in Emergency Condition
Contributing factors: Human Factors; Aircraft
Primary problem: Aircraft

Narrative: We were cruising at 11500; southbound; and planning on overflying ZZZ to continue toward ZZZ1 for a training flight. We were over the mountainous area when I noticed the engine losing 200 rpm from the cruise RPM of 2400. I immediately enrichen the mixture and pulled carb heat. Oil pressure and oil temp were in the green. My safety pilot squawked 7700 and declare over CTAF. Multiple planes on CTAF were offering assistance and advice regarding ZZZ and the area surrounding it. I'm familiar with the area and just flown that same route yesterday so I know that we cannot make it to ZZZ from where we were at and there is no other airport insight. I noticed that ZZZ2 is listed at a private airport off of my 10 o'clock but I'm not familiar with that airport and foreflight doesn't give me the information needed quickly enough. We were preparing to land on a field somewhere in city; state as the engine performance deteriorates to the point where there is barely enough to keep us afloat at 80 mph. After troubleshooting the engine; messing around with the mixture and power setting; I was able to find the sweet spot where the engine runs smoothly and no longer vibrating but full power wasn't restored; we can now pick up some speed but not quite enough to climb back up to 11500 from 10000. We were still continuing southbound toward ZZZ at around 10000; the engine did sputter really badly at one point but it felt like we got full power back shortly after the rough sputter. Another plane got on CTAF and ask about the 7700 aircraft; I identified ourselves and stated our intention of going for ZZZ. We were told to squawk VFR as Center cannot offer us any help from that side of the mountain. I complied and squawked VFR. We got over ZZZ and I elected to circle the airport roughly 1 mile to the south off of the right base for runway XX as there was a glider being tow and a tow plane taxing on the runway at ZZZ. While circling; I started to play around with the mixture/power setting to ensure that we actually have full power back and the engine will not die on us as we descent down to land at ZZZ. ZZZ downwind for both XX and XY have rising terrain on both side; my main concern was that the engine dies and we have nowhere to glide to. We did contemplate turning back north toward our home airport as the terrain is much more forgiving at ZZZ3 but ultimately decided that flying back north would add way too many unnecessary risks. I started a slow spiraling descent with some power to make sure that the engine will not die. Clear the engine every 1000 ft of altitude that we lose. We were also able to communicate with the glider and the tow plane and they both cleared the runway for us. I entered the right base for XX and landed the plane. The local mechanic after looking over the engine and listen to how the engine act in the air; he stated that it was probably carb ice; which is surprising considering the OAT was 10C; we weren't in moisture and I didn't see an AIRMET Zulu. The biggest factor on us squawking 7700 and declaring mayday so quickly is that we were over some quite rugged terrain and the power loss was quite drastic. We were around 4000 ft AGL; possibly 5000 ft AGL at city and not within gliding range of ZZZ. This is also my first inflight emergency where my engine stops producing power. We both learned about carb icing in school but never experience it in real life. Knowing what we know now. Squawking 7700 and declaring mayday right away might have been a bit premature; we should have to spend a couple of minutes to troubleshoot the problem first as the engine was producing power; oil pressure/oil temp were good. My safety pilot was also not too familiar with the plane and he didn't know what the plane is truly capable of as far as gliding distance goes. His main concern was to put the plane down in a field; he was afraid that we would crash into a mountain trying to make it to [another city]. When we were over ZZZ; he wanted us to descent as quickly as possible and land at ZZZ without troubleshooting the engine first; which is what I was doing. I wasn't comfortable with descending when I know the engine is running fine up here and the overly sensitive mixture setting could possibly contribute to the reason why the engine almost died on us. I didn't want to descent into denser air that could possibly mess with the mixture and kill the engine. We were having a little conflict in the cockpit in the middle of an emergency on what we should do. [Another city] not having weather reporting capability along with the glider being towed on the runway while not monitoring CTAF also added additional stress to our situation. This in-flight emergency highlighted the importance of who's doing what during an emergency; those conversation needs to happen on the ground; not in the middle of an emergency.




Synopsis: C172 pilot reported a loss of power inflight resulting in an emergency landing.