A MECHANIC ON A FIELD TRIP REPLACING AN OUTBOARD FLAP; INBOARD TRAILING EDGE PANEL ON A DEHAVILLAND DHC-8-400 ACFT; NOTES THE VISUAL DIFFERENCES FROM THE REMOVED PANEL. ENGINEERING STILL APPROVED THE USE OF PANEL.

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I WAS IN ZZZ TO REPLACE AN OUTBOARD FLAP; INBOARD TRAILING EDGE PANEL. I NOTED WRONG PART NUMBER WAS DELIVERED. WORKED WITH ENGINEERING TO RECTIFY PART NUMBER ISSUES. GOT VERBAL SAYING IT WAS INTERCHANGEABLE; DIFFERENCE WAS IN THE INBOARD END RIB OF PANEL. DIFFERENCES VISUALLY NOTICEABLE; TOOK PICTURE OF AREA WITH NOTES; SUBMITTED TO ENGINEERING. GOT REPLY BACK SAYING IT WAS A BONDED CHANNEL. INSTALLED TRAILING EDGE; GOT ENGINEERING CHANGE FOR USE INTERCHANGEABILITY AND SIGNED OFF PAPERWORK ALONG WITH QUALITY CTL INSPECTION. RETURNED TO YYY THAT DAY. ACFT RETURNED TO SVC. WHEN I GOT BACK TO WORK; I PULLED UP A DRAWING TO DO A GUT CHK ON SOME INFO RECEIVED ON CHANNELS AND FOUND FASTENERS IN DRAWING NOT INSTALLED ON TRAILING EDGE RIB CHANNELS. I NOTIFIED LINE MAINT SUPVR; MAINT CTL; AND ENGINEERING. APPROPRIATE ACTIONS WERE TAKEN BY ALL. ENGINEERING CONTACTED BOMBARDIER AND HAS SINCE GOT A RE-DISPATCH FOR ACFT FOR RETURN TO SVC AS IS. JUST DID A SELF-CHK AND DIDN'T GET A GOOD FEELING OF THE ANSWER I GOT FROM ENGINEERING ABOUT PILOT HOLES IN RIB CHANNELS AND DID A LITTLE MORE RESEARCH AND FOUND FASTENERS TO BE MISSING IN CHANNELS. NOTIFIED MAINT SUPVR; MAINT CTL; WHICH SWAPPED OUT ACFT WITH SPARE; AND ENGINEERING CONTACTED FOR MORE INFO. LACK OF DOCUMENTATION ON INTERCHANGEABILITY AS TO WHAT IS REQUIRED WHEN CHANGING PARTS AND CONFLICTING DRAWINGS. WHEN DEALING WITH INTERCHANGEABILITY ISSUES; ENSURE ALL DOCUMENTATION ON DIFFERENCES ACCOMPANY THE ENGINEERING CHANGE FOR PROPER INSTALL OF NEW PART. NOT JUST A STATEMENT SAYING THEY ARE INTERCHANGEABLE.