A320 FLT CREW HAS IR2 FAILURE IN CRUISE AND ACCIDENTALLY TURNS OFF IR3 DURING ATTEMPT TO SET IR2 TO HEADING MODE. THIS CAUSES THE FLIGHT CONTROLS TO REVERT TO ALTERNATE LAW AND MAKES AUTOPILOT AND AUTOTHRUST INOPERATIVE.

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WE WERE IN CRUISE FLT SHORTLY AFTER LEVELING OFF FROM CLBOUT FROM SEA. I WAS PF. AN IR2 NAV ERROR WAS DISPLAYED. THE CAPT USING HIS QRH; ATTEMPTED TO RESET THE IR2 HDG BY SELECTING ATT ON THE IR2 SWITCH. HE ATTEMPTED TO RESET THE SWITCH AGAIN BUT ACCIDENTALLY GRABBED IR3. SELECTING ATT ON IR3 NOW GAVE US A DUAL IR FAILURE AND WE LOST OUR PRIMARY MEANS OF NAV. THE ECAM LIT UP RED; THE AUTOPLT DISCONNECTED; AND THE AUTOTHROTTLES WENT TO THRUST LOCK. THE FLT DIRECTOR WAS LOST AND MY MAP DISAPPEARED. WE CONTINUED THE FLT AND I HAND FLEW THE AIRPLANE USING MANUAL THRUST. WE MANUALLY TUNED NAVAIDS ALONG THE RTE; FOLLOWED THE ECAM AND COMPLETED THE FLT WITHOUT FURTHER INCIDENT. THE EVENT OCCURRED BECAUSE WE DID NOT USE THE GUARD AND 'CONFIRM' PROC BEFORE MOVING AN IR SWITCH. AS SOON AS THE ECAM TURNED RED I LOOKED AT THE CAPT AND SAID; 'THAT'S WHY THEY ARE CONFIRM SWITCHES.' UNFORTUNATELY I THOUGHT OF THAT A FEW SECONDS TOO LATE. 1) EVEN THOUGH I WAS PF; THE AIRPLANE WAS ON AUTOPLT AND I SHOULD HAVE BEEN MONITORING THE CAPT MORE CLOSELY. 2) USE THE GUARD AND 'CONFIRM' PROC BEFORE TOUCHING AN IR SWITCH! SUPPLEMENTAL INFO FROM ACN 764050: ENRTE ZZZ1-ZZZ2 LEVEL AT FL370 WE RECEIVED MCDU MESSAGE OF 'CHK IR2 POS.' IN CHKING THIS I NOTICED THE IR POS DRIFTING BEYOND 5 NM OFF COURSE. LOOKING IN MY QRH TO SEE IF I COULD CORRECT THIS I TURNED TO IR ALIGNMENT IN ATT MODE SECTION. I FOLLOWED THE PROCS AND GOT THE IR BACK ON THE CORRECT HDG. OUT OF CURIOSITY I PUT IR2 BACK TO IR MODE. NOTHING CHANGED SO I WENT TO GO BACK TO ATT MODE. BY MISTAKE I GRABBED THE IR3 SWITCH AND TURNED IT TO ATT PUTTING US INTO ALTERNATE LAW WITH NO AUTOPLT OR AUTOTHRUST. WE CONTINUED THE FLT UNEVENTFULLY AND LANDED WITHOUT INCIDENT. I MISUNDERSTOOD THE QRH DIRECTIONS AND THOUGHT I COULD REALIGN THE IR FORGETTING THAT I CAN'T DO THAT WHILE AIRBORNE. I WAS TIRED AS THE DEP TIME WAS VERY EARLY. I SHOULD HAVE WAITED FOR AN IR FAILURE BEFORE MESSING WITH IT AT ALL BUT I THOUGHT I COULD HEAD IT OFF BEFORE IT FAILED. ALSO; I GOT COMPLACENT AND DIDN'T VERIFY THE CORRECT IR SWITCH BEFORE TURNING IT. THE SWITCHES BEING IN A 1-3-2 ORDER ALSO MAY HAVE CONTRIBUTED TO MY TURNING THE WRONG SWITCH.