AN A320 FO INADVERTENTLY SELECTED MAX AUTO BRAKES BEFORE LNDG. THE CREW DID NOT REALIZE MAX BRAKING WAS SELECTED UNTIL IT WAS APPLIED DURING LNDG.

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AFTER A STABILIZED; NOT RUSHED APCH; AND A SMOOTH LNDG; MAX AUTO BRAKES ENGAGED AFTER SPOILER DEPLOYMENT. AS THE PF; I REACHED OVER AND IMMEDIATELY DISCONNECTED THE AUTO BRAKES WITH THE SWITCH. AT THIS POINT IN TIME I THOUGHT WE HAD AN AUTO BRAKE MALFUNCTION. AFTER EXPLAINING THE ABRUPT STOP TO PAX AND FLT ATTENDANTS; WE CONTINUED TO THE GATE. DURING THE TAXI IN; THE FO TOLD ME HE HAD INADVERTENTLY SELECTED MAX AUTO BRAKES WHEN HE MEANT TO SELECT 'TERRAIN ON' SWITCH. WE HAD THE WX RADAR ON FOR ARR; HE SWITCHED OFF THE WX RADAR AND WAS ATTEMPTING TO TURN ON THE 'TERRAIN ON' SWITCH. HE TOLD ME HE MUST HAVE SELECTED THE MAX AUTO BRAKES JUST BEFORE THE LNDG GEAR WAS EXTENDED. ALL CHKLISTS AND NORMAL CALLOUTS WERE ACCOMPLISHED AND COCKPIT DISCIPLINE WAS VERY GOOD. I DID NOT CATCH THE AUTO BRAKE LIGHT BEING ILLUMINATED DURING THE NORMAL CHKS. I DID CONFIRM GEAR DOWN; FLAPS DOWN; AND LNDG MEMO GREEN. AFTER COMPLETING THE SHUT DOWN PROCS; WE DID AN INSPECTION OF WHEELS AND TIRES AND HAD THE WHEELS CHOCKED; THEN RELEASED BRAKES. BRAKE TEMPS REACHED 480 DEGS ON ONE OF THE BRAKES. NO DAMAGE WAS NOTED ON WHEELS AND TIRES. I CALLED MAINT AIRFRAME CTLR AND TOLD HIM EXACTLY WHAT HAPPENED; HE SAID NO FURTHER MAINT ACTION WAS REQUIRED. THE FO TOLD ME HE THOUGHT FATIGUE HAD CONTRIBUTED TO HIS MISTAKE. IT WAS OUR FIRST LEG TOGETHER AND I DID NOT NOTICE ANY FATIGUE. LESSONS LEARNED; EXPECT THE UNEXPECTED AND ALWAYS CROSS CHK AUTO BRAKE SELECTION. WHY DID AIRBUS NOT INCLUDE AN ECAM CAUTION WARNING WHEN MAX AUTO BRAKES ARE SELECTED IN FLT? CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CAPT WAS VERY SURPRISED AFTER THE FACT THAT THE ECAM DID NOT ANNUNCIATE THE SELECTION OF MAX BRAKES. AT HIS ACR; MAX AUTO BRAKE IS PROHIBITED. THE QUESTION THEN IS; IF SELECTED AND USE IS PROHIBITED; WHY NOT ALERT ON SELECTION PRIOR TO LNDG. HE BELIEVES THAT THE FO'S ACCIDENTAL MAX SELECTION INSTEAD OF TERRAIN RADAR ON; WAS MERELY COMPLACENCY OR FATIGUE. SUPPLEMENTAL INFO FROM ACN 659409: HUMAN FACTORS WAS A FACTOR; IT WAS A LONG DAY.