On May 28, 2018, about 0930 central daylight time, an Aeronca 58B, N47252, impacted terrain during a forced landing near Tekamah, Nebraska. The pilot and passenger received serious injuries; and the airplane sustained substantial damage. The airplane was owned and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed at the time of the flight, which was not on a flight plan. The airplane departed about 0845 from Tekamah Municipal Airport (TQE), Tekamah, Nebraska, on a local flight. The pilot reported that he departed from his private airstrip located at his residence about 0700 and flew to TQE to pick up the passenger. While at TQE, he topped off the fuel and attached two American flags, which were about 3 ft X 5 ft in size, to the airplane's struts. He attached the flags because the flight was a "tribute flight" over two memorial services being held in the local area. The flight departed TQE about 0750 and proceeded to fly over Tekamah Cemetery, and then flew over to Summit Lake and circled it twice. They overflew some neighbors' homes and then went to the pilot's airstrip and landed around 0810. About 0830, he departed to fly over the Craig Cemetery at 0900, and he noted that the engine was running fine. However, while flying over Craig Cemetery, the pilot noticed the engine was not running properly, so he headed toward TQE, located about 8 nautical miles (nm) east, to drop off the passenger. He stated that the engine was getting worse en route to TQE and not developing full power, with maximum rpm around 1,500 rpm. Although the engine was not developing full power, he continued to fly to TQE, hoping he could make it to the airport. The airplane continued to descend, and it impacted a ditch located 3 nm from TQE during the forced landing. The pilot stated that he should have landed in a flat field when the opportunity was possible, instead he "kept flying into a situation where there were no options." A Federal Aviation Administration (FAA) inspector examined the wreckage at the accident site. He stated that there were flat bean fields located near the accident site, but the wreckage was found in a ditch. There were no apparent landing or skid marks leading to the ditch. The examination of the wreckage revealed that the wooden propeller blade tips were broken. The propeller spinner exhibited features consistent with torque. He was able to rotate the engine crankshaft one revolution. The carburetor was separated from the mount but was held on by the throttle cable. The flight controls exhibited continuity from the cockpit to the flight control surfaces. Fuel was present in the fuel tanks. The FAA inspector reported that he interviewed the pilot. During the interview, the pilot did not recall pulling carburetor heat ON. The pilot stated that he did not have a problem with carburetor icing before. The examination of the engine confirmed drivetrain continuity when the engine was rotated. Thumb compression was observed on all four cylinders, although the compression on cylinders No. 1 and 2 appeared "weak." All magneto leads checked good and the engine timing was verified at 30° before top dead center (TDC). All spark plugs produced an electrical spark, although the spark plug gaps for No. 1B, 3T, 4B, and 4T were greater than .016 to 0.21 inch specified. The carburetor floats were checked for freedom of movement. The inspection of the throttle plate and throttle arm revealed no defects. At 0854, the surface weather observation at TQE was wind 260° at 3 kts; 10 miles visibility; few clouds at 8,500 ft; temperature 26° C; dew point 18° C; altimeter 29.92 inches of mercury. Based on the temperature and dew point about the time of the accident, the conditions were favorable for serious carburetor icing at glide power.