On August 15, 2021, about 1457 mountain daylight time, a Cessna C177RG, N8029G, was substantially damaged when it was involved in an accident at Albuquerque International Sunport Airport (ABQ), Albuquerque, New Mexico. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that, shortly after departure from St. Johns Industrial Air Park (KSJN), St Johns, Arizona, the airplane did not perform as expected. The pilot said that he noticed that the main landing gear did not completely retract, so he diverted to ABQ. Despite multiple attempts to cycle the landing gear, which included utilizing the emergency landing gear extension procedures, he was able to extend the nose landing gear, but he was unable to obtain a positive down and locked indication on the main landing gear. As fuel levels decreased, the pilot elected to land the airplane with the main landing gear in the retracted position. Postaccident examination of the airplane by a Federal Aviation Administration inspector revealed that hydraulic fluid on the undercarriage of the airplane behind the nose landing gear wheel well and the fluid level for the landing gear power pack indicated empty. Hydraulic fluid was added to the landing gear power pack and a landing gear swing test was performed. The landing gear extended but would not retract. The nose landing gear up hydraulic flex line showed signs of leakage. The hydraulic flex line was disconnected, and pressure tested with 200 ft pounds of nitrogen. A leak in the hydraulic flex line was identified near the top of the line, but well below the fitting. During normal operation, the hydraulic flex line is pressurized to about 1,500 ft pounds. No issues were noted with the emergency landing gear extension system. A review of the airplane’s maintenance records could not determine the age of the landing gear hydraulic flex line or if any maintenance had been performed on the landing gear hydraulic flex line.