Incident
A certified flight instructor (CFI) and a dual student were practicing simulated instrument approaches. During one approach, the landing gear failed to extend. The pilots attempted to extend the gear using both the normal and emergency systems, but neither was successful.
Landing
Subsequently, an approach was made to Runway 17 for a wheels-up landing. To minimize the risks of sparks and fire, the CFI elected to land the aircraft on dirt short of the runway threshold, then allow the aircraft to skid onto the paved runway. However, the CFI was unaware of a 6-inch lip at the runway threshold. During the wheels-up landing, the aircraft struck the raised lip, resulting in a hard impact. The CFI received a compression fracture of his back as a result of the impact.
Findings
A post-accident examination of the hydraulic power unit revealed that a 'lee plug' had blown out. With the plug out, no engine-driven or emergency pump pressure could have been applied to the gear extension system.