On July 8, 2010, at 2006 central daylight time, a Cessna 210L, airplane, N2157S, was substantially damaged when its right main landing gear collapsed while landing at Ellington Field Airport (EFD) Houston, Texas. The pilot, who was the only occupant, was not injured. The airplane was registered to a private individual and was operated by Air Transit Solutions LLC. Visual meteorological conditions (VMC) prevailed at the time of the accident and an instrument flight rules (IFR) flight plan was filed for the 14 Code of Federal Regulations Part 135 on-demand cargo flight. The airplane departed the Castroville Municipal Airport (CVB) Castroville, Texas, at 1700 and was en route to EFD. During approach to EFD, the pilot moved the landing gear position handle to the down position, the hydraulic gear motor started, and the landing gear started to extend. The pilot did not receive a green gear down indicator light and he visually confirmed that the landing gear did not appear to be fully extended. The pilot then executed a go-around and departed the traffic pattern to trouble shoot the gear extension problem. The pilot conferred with his company via radio and completed a number of checklist items including a "G maneuver". All of the attempts to extend the landing gear did not work, so the pilot prepared for a gear-up landing. During touchdown the left main landing gear and the nose landing gear remained down and locked and the right main landing gear collapsed. The airplane veered off the right side of the runway and came to rest in a grassy area adjacent to the runway. During the landing, the right wing contacted the ground resulting in substantial damage to the right wing and the right horizontal stabilizer. The mechanism for landing gear extension and retraction in the Cessna 210L is accomplished by hydraulic actuators powered by an electrically driven hydraulic power pack or by use of an emergency extension hand pump. Sufficient hydraulic fluid under pressure is required to operate the hydraulic actuators and to operate the up and down locks. During examination of the hydraulic system a hydraulic line for the landing gear was found separated from its respective fitting. The separated line and adjacent wheel well area were found saturated with hydraulic fluid. The manufacturer’s maintenance manual requires that all rubber hydraulic lines should be replaced each 1000 hours or five years. During a review of the airplane’s maintenance records, there was no annotation found that indicated that rubber hydraulic lines had been replaced within the manufacturer’s recommended interval. Visual examination of the separated line showed that it did not appear to have been recently replaced, but this examination was not conclusive with regard to the length of service of the installed hydraulic line.