On May 22, 2013, about 1730 mountain daylight time, a Diamond DA-20-C1 airplane, N571MA, was substantially damaged during a forced landing at Centennial Airport (KAPA), Englewood, Colorado. The flight instructor and student pilot received minor injuries. The airplane was registered to 5280 Flying Club LLC and operated under the provisions of 14 Code of Federal Regulations Part 91 as an instructional flight. Day visual meteorological conditions prevailed for the local flight, and no flight plan had been filed. The flight instructor stated that the student pilot was flying a visual approach to a full stop landing at KAPA. While on final approach, the engine became unresponsive to throttle movement. The flight instructor took control of the airplane and attempted to restart the engine. With no increase in engine power, a forced landing was made and the airplane touched down just short of the runway threshold. After touchdown, the airplane rolled onto soft terrain and nosed over to an inverted position. During the engine examination, Federal Aviation Administration (FAA) personnel discovered that the engine throttle lever and throttle cable were disconnected. The bolt normally connecting these two components was located at the bottom of the engine cowling. A self-locking nut (Diamond part number MS21042-3), which normally secures this bolt, was missing and not located. No other anomalies were noticed with the engine. FAA review of airplane records indicated that the engine was removed and re-installed on March 15, 2013 to facilitate the repair of a loose crankcase stud. The airplane flew 100.1 hours after engine re-installation until the accident.