What was found
ON APPROACH, THE CREW MADE 3 ATTEMPTS TO EXTEND THE GEAR WITH NO SUCCESS. IAW THE QRH, THE CREW PERFORMED A MANUAL GEAR EXTENSION. EXTENSION WAS SUCCESSFUL. AS A PRECAUTIONARY MEASURE, THE CREW PERFORMED A TOWER FLYBY. THE TOWER VERIFIED THAT THE GEAR WAS DOWN AND LOCKED. AN EMERGENCY WAS DECLARED AND THE PASSENGERS BRACED. THE LANDING WAS UNEVENTFUL AND THE AIRCRAFT TAXIED TO THE GATE. MAINTENANCE WAS ABLE TO DUPLICATE THE DISCREPANCY WITH THE AIRCRAFT ON JACKS. MAINTENANCE REPLACED THE FOLLOWING COMPONENTS: VALVE, LANDING GEAR SELECTOR - TSR - 761.2 VALVE, LANDING DOOR SELECTOR - TSR - 761.2 VALVE, SAFETY - TSR - 24652.1