On August 16, 2012, about 2154 central daylight time, the pilot of a Piper PA-24-260, N8546P, made a forced landing on a rural road 3 miles southwest of Holton, Kansas. The pilot and a pilot-rated passenger were seriously injured. Another passenger sustained minor injuries. The airplane was substantially damaged. The airplane was registered to N8546 PAPA, LLC, Tecumseh, Kansas, and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a business flight. Visual meteorological conditions prevailed at the time of the accident, and no flight plan had been filed. The cross country flight originated in Mitchell, South Dakota about 2030 and was en route to Topeka, Kansas. According to the pilot's accident report, after cruising at 7,500 feet mean sea level (msl), he began a 700 foot per minute descent about 37 miles form Topeka. About 6,500 feet msl, he and his passengers smelled something burning and smoke began to fill the cockpit. There was a loss of oil pressure, engine sounds changed, and the propeller oversped to high rpm. Shortly thereafter, the engine seized. The pilot declared an emergency with the Kansas City air route traffic control center. The pilot said the sky was overcast, there was no moon, and the ground was indistinguishable. The pilot then saw automobile headlights, and he aligned the airplane with the lights. The pilot saw telephone poles and trees. He attempted to skim the tree tops, but one of the trees tore the right wing off mid-span and the left wing broke off when the airplane impacted the road and nosed down into a ditch. Two Federal Aviation Administration inspectors examined the airplane. The airworthiness inspector said oil covered the engine components in the aft section of the engine compartment, and the oil-soaked right magneto was hanging by spark plug wires. The inside radius of the magneto spacer bore nicks and scratches around the entire circumference. There was also a hole and crack in the engine case above the number 3 cylinder. The engine, a Lycoming TI0-540-D4A5 (serial no. RL-6852-48), was installed on the airplane on May 5, 2005, after undergoing a major overhaul. The most recent annual inspection was accomplished on July 2, 2012, at a tachometer time of 8545 hours, about 32 hours before the accident. On August 10, 2012, the right magneto was removed and a new magneto was installed, which was about 7 hours before the accident occurred. The FAA inspectors interviewed the mechanic who had replaced the magneto. He told the inspectors he could not recall if he had torqued the magneto attachment nuts.