A B737-300 WAS ISSUED TWO INSPECTIONS FOR FUSELAGE CRACKS THAT USED DIFFERENT REPAIR PROCEDURES. THREE MECHANICS ARE LATER INFORMED THEY DID NOT USE THE CORRECT REFERENCE PROCEDURE FOR A RT UPPER SKIN REPAIR.

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ACFT WAS ISSUED 2 SPECIAL INSPECTIONS THAT INVOLVED FUSELAGE CRACKS. A CRACK WAS DOCUMENTED ON BOTH INSPECTIONS. I FAILED TO NA ONE DOCUMENT. THE SECOND SPECIAL INSPECTION WAS BEING USED FOR THE REPAIRS. THIS CRACK LOCATION IS OVERLAPPED BY BOTH SPECIAL INSPECTIONS. SUPPLEMENTAL INFO FROM ACN 807356: OUTER FUSELAGE SKIN OF ACFT WAS CRACKED AND REPAIRED PER SRM AS STATED IN THE SPECIAL INSPECTION. ANOTHER SPECIAL INSPECTION WAS ISSUED AT SAME TIME AND THE CRACK BEING IN THE CHEM MILL POCKET DID APPLY TO THIS AIRWORTHINESS DIRECTIVE. AN OVERSIGHT ON MY PART OCCURRED WHEN THE ENGINEERING ORDER WAS NOT FOLLOWED PER THE SPECIAL INSPECTION. SRM REF THAT THIS REPAIR WAS NOT FOR THIS LINE NUMBER ACFT. SUPPLEMENTAL INFO FROM ACN 807350: I WAS OFFICIALLY A FLOATER; MEANING I WAS TO HELP OUT WHERE NEEDED ON THE ACFT. I WAS TOLD A CRACK WAS FOUND; AND SINCE I HAVE BEEN WANTING TO LEARN SHEET METAL; I VOLUNTEERED FOR THE JOB. SINCE THE CRACK WAS FOUND DURING THE SPECIAL INSPECTION; WE WERE DRIVEN TO THE SRM FOR A REPAIR; OR SO WE THOUGHT. HAD WE SEEN THIS PARTICULAR ACFT WAS NOT EFFECTIVE FOR AN SRM REPAIR AT THIS LOCATION; WE WOULD HAVE NOT CONTINUED ON. WE THOUGHT WE HAD A GOOD REPAIR PICKED OUT AND WENT TO WORK. WE FINISHED THE ENTIRE REPAIR. THE GUY I WAS WORKING WITH SAID I SHOULD SIGN OFF THE REPAIR SINCE IT WAS MY FIRST. I SAID GEE; OK; SWELL; AND HERE WE ARE NOW. THE ACFT WAS CLOSED UP AND SENT OUT TO XXX; I THINK; AND IS WHERE IT WAS TAKEN OUT OF SVC; DUE TO A PAPERWORK AUDIT WHICH CAUGHT THIS WHOLE FIASCO; THANK GOD. XXX THEN TORE OFF MY INCORRECT PATCH AND INSTALLED A MORE APPROPRIATE ONE. I THINK MY SHEET METAL DAYS ARE OVER; REGRETFULLY. I WAS ALSO NOTIFIED I MIS-CHKED THE RII BOX ON THE SIGNOFF ON THE COMPUTER. CALLBACK CONVERSATION WITH RPTR ACN 807350 REVEALED THE FOLLOWING INFO: REPORTER STATED BOTH INSPECTION DOCUMENTS FOR THE B737-300 REFERENCED A DIFFERENT REPAIR PROCEDURE FOR THE SAME CRACK LOCATION ON THE RIGHT FORWARD EXTERNAL FUSELAGE SKIN LAP; ABOVE THE PASSENGER WINDOW. ONE DOCUMENT DROVE MECHANICS TO REPAIR THE CRACK USING A PROCEDURE WRITTEN BY ENGINEERING. THE OTHER INSPECTION DRIVEN BY AN AD; REFERENCED THE STRUCTURAL REPAIR MANUAL (SRM). THEY USED THE SRM FOR THE FUSELAGE SKIN REPAIR. REPORTER STATED BOTH INSPECTION PROCEDURES WERE HARD TO FOLLOW AND THEY JUST DID NOT SEE THE MAINT NOTE THAT STATED THE SRM REPAIR WAS NOT APPLICABLE TO CERTAIN ACFT LINE NUMBERS. REPORTER STATED HE WAS LATER INFORMED THE REPAIR THEY HAD ACCOMPLISHED WAS NOT REMOVED; BUT ACTUALLY CONSIDERED AN APPROPRIATE REPAIR BY THEIR ENGINEERING AND THE ACFT MANUFACTURER. BECAUSE OF THE GOOD SHEET METAL REPAIR THEY HAD ACCOMPLISHED; HIS MAINT DEPARTMENT HAS SCHEDULED HIM INTO THEIR SHEET METAL CLASSES; WHICH IS THE TRAINING HE REALLY WAS HOPING TO GET. THE DIFFERENT REPAIR PROCEDURES REFERENCED IN THE TWO FUSELAGE INSPECTIONS ARE BEING REWRITTEN FOR BETTER CLARITY.