On May 26, 2001, approximately 2345 Pacific daylight time, a Cessna T210M, N761DL, registered to and operated by a private pilot on a 14 CFR 91 personal flight from Coeur d'Alene, Idaho, to Astoria, Oregon, was substantially damaged when it departed the runway surface during a landing with the left main landing gear retracted at Portland International Airport, Portland, Oregon. The pilot had diverted to Portland International after the gear failed to extend properly on approach to Astoria. The pilot and four passengers were uninjured in the occurrence. Visual meteorological conditions prevailed at Portland, and the aircraft was on an instrument flight rules (IFR) flight plan. Landing gear extension and retraction on the aircraft is accomplished by hydraulic actuators powered by an electrically-driven hydraulic power pack. Positioning the two-position (gear up and gear down) landing gear position handle starts the electrically-driven hydraulic power pack and selects the direction of gear travel. After the handle is positioned, the electrically-driven hydraulic power pack creates pressure in the system and the landing gear is actuated to the selected position. A hand-operated hydraulic pump is provided for extension of the landing gear "in the event of a hydraulic system failure" (according to the pilot's operating handbook). The pilot reported that upon his final descent into Astoria, the gear did not extend normally. He stated that when the gear lever was moved to the "gear down" position, the gear released from the wells but did not move forward into the locked position. He reported that recycling the gear extension handle proved ineffective; the gear motor ran but the gear would neither extend nor retract. He reported that the emergency gear extension procedure also proved ineffective. The pilot stated that he then checked the hydraulic fluid level and found the hydraulic reservoir empty (he also stated that he had checked this reservoir approximately 2 weeks/10 flight hours before the accident, and found the fluid level normal.) The pilot reported that he attempted to refill the reservoir inflight with two quarts of aviation motor oil, 1 liter of water and 12 fluid ounces of soda, but that this was also ineffective. He stated that the gear motor ran each time the gear lever was moved, but that after numerous attempts to cycle the gear, the circuit breaker eventually popped when the gear lever was moved. The pilot reported that he then attempted to obtain assistance on the radio from several sources including Seattle Air Route Traffic Control Center, Astoria UNICOM, Astoria Coast Guard, several pilots on the frequency, Portland Approach Control, and Portland Tower. He stated that ultimately, his 17-year-old son opened the cabin door and was able to pull the right main landing gear into the down-and-locked position. He stated he was also able to pull the left main gear into the down position, but that it would not lock. The pilot reported that he eventually diverted to Portland International to attempt a landing. He stated that he attempted to raise the right main gear so the main gear would be symmetrical for the landing, but that he could not unlock the right main gear. He stated that with fuel low, a landing was made on Portland runway 28R. As the aircraft touched down on the runway, its fuselage tipped about 30 degrees left wing down. The aircraft initially slid straight ahead, then made a slow 180-degree turn to the left and came to rest in the grass alongside runway 28R. The pilot reported that a postflight inspection revealed that a hydraulic line in the nose gear well had burst. The Cessna T210M pilot's operating handbook states that the hydraulic system fluid level should be checked at 25-hour intervals. Appendix A to 14 CFR 43, paragraph c(8), classifies "replenishing hydraulic fluid in the hydraulic reservoir" as preventive maintenance, which may be accomplished by a certificated pilot who owns or operates the aircraft under certain conditions specified by 14 CFR 43.3(g). Preventive maintenance is required to be logged in the aircraft logbook as specified by 14 CFR 43.9. The hydraulic system fluid level check referenced by the pilot in his NTSB accident report was not found in a copy of the aircraft logbook furnished by the pilot; however, the logbook entry for the aircraft's most recent annual inspection (August 29, 2000, approximately 70 flight hours before the accident) did indicate that a gear retraction and emergency extension test was performed during that inspection, and that the hydraulic power pack was also serviced at that time.