The pilot reported that he was practicing a simulated engine-out visual approach to the asphalt runway. He extended the landing gear on short final and believed it was down and locked; however, after touchdown, the left and right main landing gear retracted into their respective wheel-wells. A witness at the airport who observed the accident stated that the airplane's main landing gear was not fully extended when the airplane touched down on the runway. The pilot stated that he did not hear the aural landing gear warning horn prior to landing and he did not recall if the green (landing gear down) landing gear position indicator lights were illuminated prior to landing. The airplane sustained substantial damage to the right horizontal stabilizer. Initial postaccident examination of the airplane, which included a check of the landing gear warning system and a landing gear retraction test, did not reveal any anomalies. Subsequent additional examination of the landing gear system, which included multiple landing gear extension-retraction cycles revealed a faulty hydraulic power pack contactor, which resulted in intermittent extension of the landing gear. Review of the airplane's pilot operating handbook, normal procedures, before landing checklist, included: "4. Landing Gear – CHECK (observe main gear down and green indicator light on)."