A B737-700 HAD #2 VHF ANTENNA REPLACED IN MAY 2005. ANTENNA DEPARTED THE ACFT 5 MONTHS AFTER INSTALLATION. RPTR SUSPECTS ANTENNA STRUCK BY BELT LOADER.

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SEP/FRI/05 AT XA10 DURING INFORMAL QUESTIONING ON THE HANGAR FLOOR; 2 FAA INSPECTORS BROUGHT IT TO MY ATTN THAT THEY WERE INVESTIGATING AN OCCURRENCE ON ACFT #X IN WHICH THE #2 VHF ANTENNA HAD FALLEN FROM THE ACFT NEAR THE ARPT. THEY QUESTIONED ME DUE TO THE FACT THAT MY EMPLOYEE NUMBER WAS WRITTEN ON THE ANTENNA'S SVCABLE TAG IN THE 'INSTALLED BY' BLOCK. UPON MY INVESTIGATION THEREAFTER MY RECOLLECTION OF MY INVOLVEMENT WAS REFRESHED AS TO HAVING ONLY PREPARED THE ANTENNA FOR INSTALLATION BY CLEANING AND PREPPING THE MOUNT SURFACE TO WHICH THE ANTENNA WOULD BE ATTACHED. THAT SURFACE WAS THEN INSPECTED AND GIVEN APPROVAL TO HAVE THE #2 ANTENNA INSTALLED. AT SHIFT CHANGE THE JOB OF INSTALLATION WAS GIVEN TO ANOTHER MECH. SUPPLEMENTAL INFO FROM ACN 673630: ON MAY/MON/05 I INSTALLED THE AFT LOWER VHF ANTENNA ON ACFT X IN ZZZ. I DO NOT REMEMBER THIS PARTICULAR INSTALLATION BECAUSE OF THE TIME THAT HAS LAPSED. THERE IS A COMPANY MAINT PUB TIP SHEET OUT THAT ALLOWS US TO USE A MESH GASKET WHICH REQUIRES NO SEALANT. TYPICALLY I WOULD CHK THE SCREW LENGTH BY ENGAGING THE FIRST SCREW THREAD AND GAUGING HOW FAR THE HEAD WAS PROTRUDING (SAME LENGTH AS THE THREADS). ON SEP/FRI/05 THE ANTENNA WAS WRITTEN UP AS MISSING. I DID NOT FIND OUT UNTIL SEP/FRI/05. I HAVE THOUGHT ABOUT WHAT COULD HAVE HAPPENED AND I CANNOT EXPLAIN HOW IT COULD HAVE COME LOOSE. I WOULD HAVE TORQUED THE 10 FASTENERS IN A SEQUENCE THAT WOULD KEEP THE ANTENNA PERPENDICULAR TO THE FUSELAGE BECAUSE THE ANTENNA CAN TILT TO ONE SIDE IF THEY ARE NOT TORQUED IN SUCH A SEQUENCE. AFTER THE BOND CHK; I WOULD HAVE TORQUED THE FINAL SCREW AND SHOOK THE ANTENNA TO SEE THAT IT WAS SECURE AFTER TOUCH-UP PAINT; I WOULD CALL INSPECTION AND THE INSPECTOR WOULD HAVE CHKED THE FASTENERS VISUALLY AND SHOOK THE ANTENNA FOR SECURITY; BEFORE HE BOUGHT BACK THE INSTALLATION. I WAS TOLD THAT THE LAST FASTENERS THAT WERE FOUND WERE ON THE L SIDE OF THE ANTENNA. IT SEEMS POSSIBLE TO ME THAT THIS COULD BE CONSISTENT WITH A BELT LOADER PUSHING THE ANTENNA TO THE L SIDE SHEARING THE R SIDE FASTENERS FIRST. I WAS ABLE TO INSPECT THE ANTENNA AND COULD SEE EVIDENCE OF ALL 10 SCREWS ON THE COUNTER SINK SURFACE. THE GALLING SEEMED MORE PREVALENT ON THE L SIDE; SUGGESTING THE R SIDE GAVE AWAY FIRST. IF THE ANTENNA WAS HANGING AT THAT POINT; IT WOULD HAVE SHEARED THE L SIDE AS SOON AS IT WAS AIRBORNE AGAIN. THIS SEEMS TO BE CONSISTENT WITH THE ANTENNA BEING FOUND AT AN ARPT. I WONDERED WHAT THE ODDS OF IT COMING OF AT THE ARPT UNLESS IT WAS DAMAGED AT THAT ARPT. I COULD NOT FIND ANY EVIDENCE OF SIDE IMPACT BUT THE LOADERS HAVE RUBBER BUMPERS THAT COULD PUSH THE ANTENNA WITHOUT GOUGING IT. SUPPLEMENTAL INFO FROM ACN 674096: I RECEIVED NOTICE THAT AN ANTENNA HAD FALLEN OFF OF ACFT. I WAS ALSO INFORMED THAT I HAD BOUGHT THE INSTALLATION DURING A MAINT VISIT SOME TIME IN MAY OF 2005. I CANNOT REMEMBER EXACTLY WHEN I BOUGHT THIS ITEM; BUT GENERALLY WHEN BUYING THE INSTALLATION OF ANY COMPONENT ON THE ACFT; I ALWAYS CHK FOR SECURITY OF INSTALLATION PER MAINT MANUAL AND OPS CHK PER MAINT MANUAL.