What was found
ON FLIGHT 3885 (JFK TO PHL) STEERING INOPERABLE CAUTION MESSAGE ILLUMINATED ON DEPATRURE FROM JFK ONCE THE GEAR WAS RETRACTED. FOLLOWED QRH DID NOT ALTER MESSAGE. STEERING DID NOT RESET AND CREW ADVISED THAT THEY WOULD NEED TOW TO CLEAR RUNWAY ON HIGH SPEED. AN EMERGENCY WAS DECLARED. LANDED LONGEST RUNWAY AT PHL. REMOVED AND REPLACED PILOT HANDWHEEL CONTROL UNIT (TILLER) IAW CRJ 200 AMM 32-51-01. TAXIED AIRCRAFT NO PROBLEMS NOTED. OK FOR SERVICE. ALL OPERATIONS CHECKS GOOD.