On August 31, 2012, about 1145 eastern daylight time, a Cessna 172M, N391R, registered to and operated a private individual, landed short of the intended runway during a precautionary landing at Flying Dollar Airport, Canadensis, Pennsylvania. Visual meteorological conditions prevailed at the time no flight plan was filed but visual flight rules (VFR) flight following was being provided for the 14 Code of Federal Regulations (CFR) Part 91 personal flight from Princeton Airport (39N), Princeton/Rocky Hill, New Jersey, to Cherry Ridge Airport (N30), Honesdale, Pennsylvania. The airplane sustained substantial damage, and there were no injuries to the private pilot, one passenger, or a dog. The flight originated from 39N about 1110. The pilot stated that the purpose of the flight was pleasure, and the estimated flight time from 39N to N30 was 52 minutes. He performed a preflight inspection of the airplane using a checklist which included using a dipstick to check the quantity of fuel in each tank, and also checking the wing fuel tanks and fuel strainer for contaminants; none were found. The left tank had about 10 gallons and the right fuel tank had about 12 gallons; both tanks contained 100 low lead (100LL) fuel. He also checked the engine oil which indicated 6.1 quarts and added 1.0 quart. Prior to departure he performed an engine run-up which included checking the magnetos. Each magneto drop was about 50 rpm. The flight departed with the fuel selector positioned to both, proceeded due North towards the destination and climbed to 4,500 feet while obtaining VFR flight following. After reaching cruise altitude, or about 5 to 10 minutes into the flight, he reduced throttle, leaned the fuel to air ratio until the engine ran rough, then enriched it slightly. Some time later, the engine sound changed but was not a loud sound. The sound he described was more like a cylinder not firing. There was significant vibration, and he ran the emergency procedures by verifying the primer was in and locked, the fuel selector was on both, placed the mixture control to full rich, then a short time later checked the magnetos noting the engine continued to run on any selection (left, right, and both). He also reported adding carburetor heat, but nothing he did corrected the situation. Since the engine was still developing some power he declared PAN PAN PAN with the controller who vectored the flight to 8N4. At that time the flight was about 6.5 miles east of there, and 3,000 feet above the field elevation. He flew towards 8N4, and with the engine still developing partial power, the controller advised him of the orientation of the runway 02/20. The wind favored runway 20, so he continued to the airport and minimized his loss of altitude. He noted that the vibration increased with decreased engine rpm, so he set the power about midrange. He flew left base to final for runway 20 (which is a 2,405 foot long grass runway) and with no flaps extended performed an aggressive forward slip to lose altitude because the flight was high. The airplane touched down a little fast, bounced a couple times, and he added some power to correct the bounce. With the end of the runway coming near and a terrain drop near the end of runway 20, he performed a go-around. He executed a 180 degree turn to land on runway 02, and on final approach the plane was 10 to 15 feet below the altitude of the runway. He pulled back on the yoke, and while flying at 40 miles-per-hour, impacted 45 degree upsloping terrain. The airplane nosed over and then all occupants exited the airplane. He later reported that at no point before touchdown did the engine quit or the propeller stop. The pilot later stated that postaccident, he went back to the airport and noticed for the first time that runway 20 is downsloping. He also stated that the airport owner acknowledged this and because of that fact, said landings are usually on runway 02, and departures are from runway 20. A postaccident examination of the airplane and engine was performed by a Federal Aviation Administration (FAA) airworthiness inspector following recovery of the airplane. Inspection of the airplane revealed an adequate fuel supply remaining with no contamination noted; the fuel strainer still had fuel inside. Examination of the engine revealed crankshaft, camshaft, and valve train continuity; no stuck valves were noted. During hand rotation of the engine, no detectable compression was noted at the No. 4 cylinder (leakage past the exhaust valve was detected). The magnetos were tightly installed and properly timed to the engine; however, one magneto “…had very little spark” during hand rotation of the engine. The bottom spark plugs were noted to be oil soaked. The fuel and air induction systems of the engine checked satisfactory. With respect to the engine, the pilot reported having to lean the fuel/air ratio to burn off carbon etc., from the spark plugs.