On February 8, 2002, approximately 1030 mountain standard time, a Cessna 172N single-engine airplane, N75616, was substantially damaged during a precautionary landing to a road following a loss of engine power near Santa Fe, New Mexico. The flight instructor and student pilot were not injured. The airplane was registered to and operated by Zia Aviation, Santa Fe. Visual meteorological conditions prevailed, and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 instructional flight. The cross-country flight departed Santa Fe Municipal Airport, Santa Fe, at 1010. In the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2), the flight instructor reported that he and the student pilot preformed a preflight inspection and an engine run-up prior to departure. No anomalies were noted with the engine during the inspection and run-up. During the takeoff roll, the student and instructor noticed a "slight [engine] roughness," the instructor "enriched the mixture," and the engine roughness ceased. After climbing approximately 300 to 500 feet per minute, the student leveled the airplane at 9,500 feet msl for cruise flight. The instructor reported that he noticed the airplane was not accelerating to the desired cruise speed. Within one or two minutes, after adjusting the mixture and applying carbuerator heat, the engine began to operate rough. The student pilot turned the airplane back toward Santa Fe with the intention to return to the airport. As the flight proceeded, the engine roughness and power loss amplified. Approximately 9 miles southeast of the airport, after realizing the airport could not be reached, the flight instructor elected to execute a precautionary landing to a dirt road. During the precautionary landing, the airplane touched down on the nose landing gear, and after impact with a ditch, the nose gear separated. The airplane then slid 50 to 100 feet, nosed over, and came to rest inverted. According to the FAA inspector, who responded to the accident site, both wings and the firewall were substantially damaged. The aircraft was recovered to a hangar for further examination. On February 11, 2002, the flight instructor, who was also a certified mechanic and maintained the airplane, and the FAA inspector examined the Lycoming O-320-H2AD (serial number L5684-76) engine. During an ignition timing check, the engine crankshaft was rotated by hand; however, "the apparent spark from each of the 8 leads was not what would be expected from this system." The Continental/Bendix D-3000 single-drive dual magneto's lower timing inspection port was removed and approximately 2 cups of engine oil drained from the magneto. It was determined that the magneto driveshaft oil seal had failed allowing engine oil to enter the magneto. A review of the maintanence records revealed that the last annual inspection was completed on May 11, 2001, at 1,515.89 hours since major overhaul. At the time of the accident, the engine had accumulated 2,030 hours since major overhaul.