AN A320 WAS DISPATCHED WITH A #2 AIR DATA REF UNIT DEFERRED AS INOP. CONTRACT TECHNICIAN ALSO RENDERED #2 INERTIAL REF UNIT INOP IN ERROR. CAUSED BY WRONG INTERP OF THE MEL SPECIAL PROCS.

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DURING PREFLT; WE OBSERVED A FAULT LIGHT IN AIR DATA REF UNIT #2. AFTER PHONE CALL TO MAINT CTL; CONTRACT MAINT WAS CALLED. 2 CONTRACT MECHS CAME TO THE ACFT AND BEGAN WORKING THE LENGTHY MEL CARD FOR AN AIR DATA REF UNIT #2 DEFERRAL. I WAS FOCUSED ON OTHER ISSUES; INCLUDING A NEW RELEASE DUE TO NOT BEING RVSM CAPABLE; ADDITIONAL FUEL; ISSUES WITH A PWR CART; AND KEEPING THE PAX INFORMED. CONTRACT MAINT RAN THE TESTS; AND THEN TURNED OFF AIR DATA REF UNIT #2 (REQUIRED BY MEL 3410E) AND ALSO TURNED OFF INERTIAL REF #2 (NOT REQUIRED BY MEL). THE FO QUERIED THE MECH AND HE ASSURED US THAT THIS WAS REQUIRED. WHEN THE MECHS WERE DONE; AND THE NEW MEL AND MAINT RELEASE WERE PRINTED; WE REVIEWED THE PREDEP INFO; INCLUDING THE NEW RELEASE; MAINT RELEASE; AND MEL. I DID NOT NOTICE THAT INERTIAL REF #2 WAS OFF. WE PUSHED BACK AND BEGAN THE ENG START AND TAXI OUT. I INQUIRED ABOUT THE ATT AND AIR DATA SWITCHES BEING IN 'FO ON 3' AND WE DECIDED THAT MADE SENSE GIVEN THE DEFERRAL. ONCE AT ALT; WE CONTINUED TO DISCUSS THE SITUTION. I RE-READ THE MEL CARD AND REALIZED THAT THE CONTRACT MECH HAD MISINTERPED THE MEL INSTRUCTIONS. WE SHOULD HAVE HAD ALL 3 IRU'S ALIGNED; AND ONLY AIR DATA REF UNIT #2 SECURED PER THE MEL CARD. ALL SYS OPERATED CORRECTLY THROUGHOUT THE FLT; AND IT WAS OTHERWISE UNEVENTFUL. I WORKED AT THE TRAINING CTR FOR 6 YRS; AND HAVE BEEN ON THE 'BUS' FOR OVER 10 YRS. MIXING UP THE INERTIAL REF 'OFF' AND THE AIR DATA REF UNIT 'OFF' IS DISCUSSED SEVERAL TIMES THROUGHOUT THE SYLLABUS. I SHOULD HAVE DEVOTED MORE PREDEP ATTN ON THE MEL. I WAS DISTR BY THE TIGHT CONNECTIONS (WE WERE ALREADY 10 MINS OVER-PLANNED DUE TO WINDS; PLUS PUSHING NEARLY 30 MINS LATE); THE RELEASE; TRACKING DOWN THE FUELER; LIMITED PWR CART AVAILABILITY; ETC. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ACTUAL DEFERRAL WAS NOT READ UNTIL AFTER DISPATCH WHEN IT WAS NOTED THE #2 INERTIAL REF UNIT WAS ALSO RENDERED INOP. ONLY THE #2 AIR DATA REF UNIT WAS PLANNED TO BE DEFERRED BUT NOW HAD BOTH UNITS DEFERRED AS INOP. THE MAINT CTLR WAS NOT CONTACTED PRIOR TO DEP TO BE CERTAIN THE CORRECT PROC WAS PERFORMED.