ACR MAINT INSTALLED THE WRONG THRUST REVERSER ON A DC9-30 ACFT AND FOUND THEIR MISTAKE AND RE-RTED THE ACFT BACK TO MAINT FOR CHANGE TO THE CORRECT PART WITHIN 48 HRS. HOWEVER; THE ACFT DID CARRY PAX BACK TO THE MAINT BASE AFTER THE COMPANY FOUND OUT ABOUT THE WRONG PART. FACTS AVAILABLE INDICATED THAT THE WRONG PART OPERATED SATISFACTORILY. THE MECHS INVOLVED HAD 23; 30; 25 AND 25 YRS EXPERIENCE RESPECTIVELY.

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ON OCT/XX/96 THE PWRPLANT FINAL ASSEMBLY SHOP PLACED THE WRONG TYPE THRUST REVERSER ON ENG #ZZZZ. THE 2 MECHS WHO INSTALLED THE THRUST REVERSER WERE DIRECTED TO INSTALL THRUST REVERSER SERIAL #XXXX ON ENG #ZZZZ. THE QEC'ED ENG WAS LATER INSTALLED ON ACFT (L SIDE) AND RELEASED FOR PAX SVC. THRUST REVERSER SERIAL #XXXX (ACR X) CLASS/CTL #YYYY) A HUSH REVERSER WAS INSTALLED ON A STANDARD DASH 7B ENG. THE PART NUMBER DIFFERENCE WAS MISSED AS A RESULT OF A SPECIFIC SERIAL NUMBER BEING REQUESTED FOR INSTALLATION; AND THE MECHS INVOLVED COMPLETED STEP #2 CARD WHICH DOES NOT DESIGNATE A SPECIFIC THRUST REVERSER NUMBER TO BE INSTALLED ON THIS MODEL ENG. THE ACFT AND NEWLY CHANGED ENG WAS RELEASED FOR REVENUE PAX SVC. 48 HRS LATER THE MISTAKE WAS DISCOVERED; THE ACFT WAS ROUTED TO ZZZ AND THE CORRECT THRUST REVERSER ASSEMBLY INSTALLED. AS A RESULT OF THIS ERROR A REQUEST FOR PUB CHANGE HAS BEEN SUBMITTED TO CORRECT ROUTINE WORK CARD TO REFLECT A SPECIFIC THRUST REVERSER CLASS/CTL NUMBER TO BE INSTALLED ON CORRESPONDING ENGS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE CORRECTIVE ACTION INDICATED HAD ALREADY BEEN TAKEN AND THAT THE FAA MET WITH HIM AND THE OTHER MAINT PERSONNEL INVOLVED IN THIS INCIDENT AND CONCLUDED THAT THE CORRECTIVE ACTION WAS APPROPRIATE AND SHOULD SAFEGUARD THIS HAPPENING AGAIN. THE FAA WILL NOT TAKE ANY CERTIFICATE ACTION AGAINST THOSE INVOLVED EXCEPT FOR THE POSSIBILITY TO THE COMPANY FOR OPERATING REVENUE FLTS BACK TO THE MAINT BASE. THERE WAS NO PROB INSTALLING THE WRONG THRUST REVERSER OR IN ITS OP ON THE ACFT.