A B737-300 WAS DISPATCHED IN NON COMPLIANCE WITH THE R ENG PYLON UPPER SURFACE ACCESS PLATES NOT SECURED.

Narrative

I; ABC WXXX AIRFRAME AND PWRPLANT TECHNICIAN #WWXXZZ; EMPLOYED AT ACR AS A&P TECHNICIAN; WAS WORKING ON OCT/SUN/99 AS AN INSPECTOR; INSPECTING BOTH ENGS ON B737-300 ACFT XYZ. AS WE FINISHED ALL ROUTINE AND NON ROUTINE TASKS; ACFT WAS RETURNED TO SVC ON THE MORNING OF OCT/MON/99. AS IT LEFT ZZZ ARPT; SOMETIME DURING FLT 3 EACH SMALL ACCESS PANELS DEPARTED FROM #2 ENG PYLON FOR UNKNOWN REASONS. I HAD DONE MY INSPECTION PRIOR TO ACFT BEING RETURNED TO SVC AND VERIFIED ALL ACCESS PANELS TO BE INSTALLED AND BEING PRESENT. AT THAT TIME ACFT WAS TURNED OVER TO ONCOMING INSPECTOR AT XA30 WHERE ENG #1 AND #2 VIBRATION SURVEY WAS SUCCESSFULLY COMPLIED WITH. ACFT THEN RETURNED TO HANGAR; THEN FINAL WALKAROUND WAS ACCOMPLISHED AND VERIFIED ALL ACCESS AND SVC PANELS TO BE SECURED. ACFT THEN WAS OPERATED ON ACR FLT XZX FROM ZZZ ARPT TO VVV; US. AFTER ARRIVING AT VVV; FLC RPTED THAT 3 ACCESS PANELS (4827R; 5828R; AND 5829R) ON TOP OF R ENG PYLON WERE MISSING. SINCE ACCESS PANELS WERE SECONDARY STRUCTURE THEY WERE PUT ON CDL PER ACR POLICIES AND ACFT CONTINUED IN SVC AND ALL 3 PANELS WERE REPLACED LATER ON. NO DAMAGE HAD OCCURRED DUE TO THIS INCIDENT.