On January 1, 2017, about 1130 central standard time, a Quicksilver GT-400 R503 experimental light sport airplane, N415HC, impacted power lines during a forced landing following a partial loss of engine power near New Braunfels, Texas. The sport pilot, who was the sole occupant, was not injured, and the airplane sustained substantial damage. The airplane was registered to and operated by a private individual as a 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed at the time of the accident and a flight plan was not filed. The local flight departed a private airstrip about 1110. According to the pilot/owner, about 15 minutes into the pleasure flight, the engine began "sputtering" and losing power. The pilot attempted to correct the problem by adjusting the throttle and applying engine primer. The attempts were unsuccessful in restoring engine power. The pilot then identified a field for a forced landing. During the forced landing, the right main landing gear struck a power line. After impacting the power line, the airplane flipped inverted, and dropped about 20 feet onto a carport rooftop. The pilot exited the airplane. Examination of the airplane by Federal Aviation Administration inspectors revealed both wings were bent and the wing fabric was damaged. No visual anomalies with the engine were noted. After the airplane was recovered from the carport, the pilot and a few friends examined the airplane and systems. The pilot noticed that one of the four engine spark plugs was loose in the cylinder. The pilot determined that the loose spark plug led to a loss of compression and partial loss of engine power during the accident flight. The pilot's safety recommendation, as noted in the pilot/operator accident report, stated "closer inspection of checking spark plugs before flight."