On April 5, 2017, at 1410 central daylight time, a Cessna 210M single-engine airplane, N1215M, experienced a right main landing gear collapse at the Detroit Lakes Airport (DTL), Detroit Lakes, Minnesota. The commercial pilot, who was the sole occupant, was not injured, and the airplane sustained substantial damage to the right horizontal stabilizer. The airplane was registered to Great Plains Leasing, LLC, Dickinson, North Dakota, and operated by a private individual under the provisions of 14 Code of Federal Regulations Part 91 as a positioning flight. Visual meteorological conditions prevailed at the time of the accident, and a flight plan was not filed. The flight departed the Moorhead Municipal Airport (JKJ), Moorhead, Minnesota, about 1350. According to the pilot, before the accident flight, the airplane had been experiencing intermittent landing gear problems, and the purpose of the flight was to bring the airplane to a maintenance facility at DTL to examine the landing gear system. Before the flight, the landing gear circuit breaker was pulled out "in order to keep the gear in the down position and eliminate the gear warning horn" for the flight to DTL. While landing at DTL, the pilot noticed the left wing slightly dropped after touchdown, and the pilot corrected with aileron to maintain runway centerline. Shortly thereafter, the pilot could feel the right main landing gear slowly collapse. The pilot was unable to maintain the airplane on runway centerline, and the airplane exited the runway surface. The airplane came to rest upright with the right main landing gear collapsed, and the right horizontal stabilizer was bent. On April 18, 2017, the airplane was examined by a Federal Aviation Administration (FAA) inspector and a mechanic. During the initial examination, the landing gear was retracted and extended multiple times. Each gear retraction was normal, and the gear extension cycle resulted in the left main and nose gear extending and locking, and the right gear extending with no movement from the downlock actuator. After loosening the hydraulic line fittings at the downlock actuator, hydraulic fluid was present at the actuator. The actuator was removed for further examination, and was found difficult to move. According to the inspector, after removal, the actuator released, and the internal spring mechanism freely moved the actuator. The actuator was disassembled with no internal problems noted. On April 24, 2017, a former pilot of the accident airplane stopped into the FAA office in Fargo, North Dakota, to discuss the accident. According to the pilot, he had previously flown the airplane in September 2016 from DTL to JKJ, and experienced an unsafe gear warning horn and advised the airplane owners. During his landing, he landed with the landing gear pump circuit break in and the gear warning horn functioning. He stated that with the landing gear pump operating (circuit breaker in), the pump pressure on the landing gear actuator held the gear in the "saddle" until the airplane was on the ground. The weight of the wheels would then keep the gear in the down position. To his knowledge, the airplane had been in storage since his flight. According to the Cessna Pilot's Operating Handbook (POH), Section 3, Emergency Procedures, Landing Gear Malfunction Procedures, all landing gear malfunction scenarios listed in the POH require the landing gear pump circuit breaker to be in the "IN" position.