On October 29, 2008, about 1959 mountain standard time, a Cessna 421C, N421PC, experienced the collapse of its landing gear during rollout at the Falcon Field, Mesa, Arizona. The airplane was owned and operated by Dry Force, Inc., Mesa. The airplane was substantially damaged, and neither the commercial certificated pilot nor four passengers were injured. Visual meteorological conditions prevailed at the time of the business flight, and an instrument flight rules flight plan was filed. The flight was performed under the provisions of 14 Code of Federal Regulations Part 91, and it originated from San Diego, California, about 1737 Pacific daylight time. The pilot reported to the National Transportation Safety Board investigator that, at the conclusion of the flight on approach to Falcon Field, he placed the landing gear selector in the down position. Thereafter, he observed that the landing gear's green position light failed to illuminate for the left gear. The pilot attempted to lower the gear several times and finally attempted to extend the gear using the emergency "blow down" procedure. None of the procedures worked. The pilot landed on runway 22 with a partially extended landing gear. The airplane touched down softly on the runway, but substantial structural damage occurred as the airplane swerved off the runway and slid to a stop. Belly skin was punctured, and several ribs were bent upward. The pilot reported that he smelled a strong odor of hydraulic fluid in the cabin. An examination of the landing gear system revealed that an aluminum hydraulic line associated with the gear's operation had ruptured beneath an Adel clamp. There was a crack in the line at a 45-degree bend near this location. The pilot also reported that the emergency gear extension system was rendered inoperative when the hydraulic leak occurred. The total time on the airframe and broken line was about 4,113 hours.