What was found
GEAR-UP LANDING ON ASPHALT RUNWAY. NO INJURIES. ALL LANDING GEAR DOORS OPENED, BUT GEAR FAILED TO EXTEND EITHER ELECTRICALLY OR MANUALLY. FAILURE CAUSED BY RESIDUE BUILT-UP ON SHAFT OF SOLENOID PN 9881201-1 PREVENTING OPERATION OF MANIFOLD ON POWER PACK. AFTER SOLENOID SHAFT CLEANED, LANDING GEAR EXTENDED BOTH ELECTRICALLY AND MANUALLY. SUBMITTER SUGGESTS INSPECTING/CLEANING SOLENOID SHAFT AT 1,000-HOUR INTERVALS.