AFTER ROUTINE OVERNIGHT MAINT AND FERRY FLIGHT; PILOT REPORTS TWO INSPECTION PANELS WERE FOUND MISSING FROM RT WING UPPER SURFACE ABOVE THE RT MLG ON AN AIRBUS A320.

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FLT WAS A FERRY TO RETURN ACFT TO LINE STATION TO RESUME NORMAL SVC AFTER CONTRACT MAINT. EXTERIOR PREFLT WAS CONDUCTED AS DIRECTED BY COMPANY PROCS ON A DARK RAMP ON AN OVCST NIGHT. THROUGH-FLT FROM ZZZ TO ZZZ1 WAS UNEVENTFUL AND NO MAINT PROBS DEVELOPED. THE NEXT MORNING; WE DISCOVERED VIA ANECDOTAL EVIDENCE; THAT THE ACFT HAD ARRIVED ZZZ1 WITHOUT 2 SMALL INSPECTION PANELS WHICH SHOULD BE LOCATED ON TOP OF THE WING NEXT TO THE WING ROOT. FURTHER INVESTIGATION REVEALED THAT THE PANELS IN QUESTION WERE APPARENTLY SITTING ON TOP OF A TOOL BOX AT THE CONTRACT MAINT FACILITY. THE PARTS IN QUESTION ARE 2 DISCS ABOUT 4 INCHES IN DIAMETER. THEY CANNOT BE SEEN FROM THE GND; AND AT NIGHT; THEY CANNOT BE SEEN FROM THE ACFT UNLESS THE TOP OF THE WING IS ILLUMINATED. AT BOTH OF OUR CONTRACT MAINT FACILITIES THERE IS NO NIGHTTIME ILLUMINATION OF THE RAMP. THE SIT COULD BE PREVENTED BY BETTER QUALITY CTL BY CONTRACT MAINT ORGANIZATIONS. IF THE COMPANY WISHES TO MAKE PREFLT AT THE TOP OF THE WING A PLT RESPONSIBILITY; THEY WILL HAVE TO PROVIDE ADEQUATE ILLUMINATION UNDER ALL CIRCUMSTANCES. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED HE IS ONE OF MANY RETIRED PILOTS WORKING FOR AN OUTSIDE EMPLOYER; WHO IS CONTRACTED BY A CARRIER; TO FERRY ACFT FOR REPOSITIONING OR SCHEDULED MAINT. THE PREFLIGHT ON THE AIRBUS A320 WAS ACCOMPLISHED IN ACCORDANCE WITH THAT CARRIER'S PREFLIGHT PROCEDURES. THESE PROCEDURES ONLY REQUIRE UPPER WING PREFLIGHT IF ICING OR SNOW IS AN ISSUE. THE TWO PANELS FOUND MISSING ARE APPROX FIVE INCHES IN DIAMETER.