What was found
PILOT ATTEMPTED TO LOWER LANDING GEAR. PILOT WAS UNABLE TO LOWER LANDING GEAR USING NORMAL OR EMERGENCY PROCEDURES WHICH RESULTED IN A GEAR-UP LANDING. FURTHER INVESTIGATION REVEALED THAT POWER PACK SECONDARY RELIEF VALVE WAS STUCK OPEN, THEREFORE, BYPASSING THE HYDRAULIC FLUID. HYDRAULIC POWER PACK WAS SENT IN FOR A TEAR DOWN AND OVERHAUL AT WHICH TIME SECONDARY RELIEF VALVE WAS REMOVED AND PLUGGED. SECONDARY RELIEF VALVE IS NOT NECESSARY FOR POWER PACK TO FUNCTION NORMALLY.