What was found
UPON CLIMBOUT THE PILOTS REPORTED THAT THE LANDING GEAR WOULD NOT RETRACT WITH THE GEAR HANDLE IN THE UP POSITION. THE GEAR INDICATION HAD SHOWN SIX GREEN LIGHTS AND 5 RED LIGHTS. MAINTENANCE REMOVED AND REPLACED THE LEFT HAND GEAR "A" SYSTEM PROXIMITY SENSOR I.A.W. EMB 120 MM 32-61-01 STEPS D,E,F,-3. THE OPERATIONAL CHECK WAS GOOD.