B757 CREW HAD MULTIPLE AUTOPLT DISCONNECTS OF ALL 3 AUTOFLT SYS.

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WHILE IN CRUISE; WE EXPERIENCED MULTIPLE OCCASIONS OF SPONTANEOUS DISENGAGEMENT OF THE L; CENTER; AND R AUTOPLTS OVER SEVERAL HRS OF FLT WHILE IN CRUISE. (PORTABLE ELECTRONIC DEVICES AUTH.) AFTER DUE CONSIDERATION OF THE SEQUENCE OF DISENGAGEMENTS STARTING IMMEDIATELY AFTER I HAD AUTH PORTABLE ELECTRONIC DEVICES; I CHKED WITH MY 'A' LINE FLT ATTENDANT. I ASKED IF ANYONE HAD TURNED ON ANY PORTABLE ELECTRONIC DEVICES THAT MIGHT HAVE CORRESPONDED WITH THE DISCONNECTS. WE COULD NOT FIND AN IMMEDIATE LINK. I THEN MADE A PA ASKING THAT ALL PORTABLE ELECTRONIC DEVICES BE SECURED AND EXPLAINED THAT WE WERE EXPERIENCING RANDOM DISCONNECTS OF THE ACFT'S AUTOFLT SYS. ALL PAX COMPLIED. THE ANOMALY CONTINUED. I ASKED THE 'A' FLT ATTENDANT TO MAKE A MORE RIGOROUS CHK OF THE CABIN; LOOKING FOR ANY ELECTRONIC DEVICE THAT MIGHT CAUSE THIS RANDOM PERFORMANCE. SHE RPTED THAT THERE WAS A PAX IN SEAT XXX THAT HAD A SIGNIFICANT HEARING IMPAIRMENT REQUIRING THAT HE USE A HEARING AID WITH HEADPHONES. THE MICROPROCESSOR WAS CARRIED IN HIS SHIRT POCKET. WITHOUT IT; HE COULD NOT HEAR AT ALL. RECALLING THAT INTERFERENCE FROM PORTABLE ELECTRONIC DEVICES IS NORMALLY ASSOCIATED WITH WIRED DEVICES NOT CONTAINED WITHIN THE MICROPROCESSOR CASE; AND FURTHER THAT PORTABLE ELECTRONIC DEVICE INTERFERENCE IS NORMALLY VERY SITE SPECIFIC; I ASKED THE 'A' FLT ATTENDANT TO MOVE THE PAX FORWARD NOT LESS THAN 3 ROWS; BUT PREFERABLY 6 ROWS. THIS WAS ACCOMPLISHED AND NO FURTHER INTERFERENCE OCCURRED FOR THE BAL OF THE TRIP. THE ONLY REASON THAT I DID NOT HAVE THE PAX TURN OFF HIS DEVICE WAS MY CONCERN WITH HIS BEING ABLE TO HEAR AND FOLLOW INSTRUCTIONS FROM THE FLT ATTENDANTS IN THE EVENT OF AN EMER. IN CONSIDERATION OF THIS; AND SINCE WE HAD NO FURTHER INSTANCE OF DISENGAGEMENT; WERE LOOKING AT GOOD WX IN CVG; AND RETAINED THE OPTION OF SECURING THE DEVICE SINCE WE KNEW WHAT THE CULPRIT WAS; I WAS VERY COMFORTABLE WITH THIS COURSE OF ACTION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CREW WAS FLYING A B757- 200 ACFT FROM SEA TO CVG. THE CAPT STATED THE AUTOFLT DISCONNECTS BEGAN ABOUT THE TIME THEY REACHED CRUISE; AT FL370. PROBS LASTED FOR THE NEXT 3-4 HRS. THE CAPT FURTHER SAID; DURING THIS TIME THE COCKPIT ROUTINE WAS DISRUPTED EXCESSIVELY; THAT WITH 3 AUTOPLTS HE HAS NEVER HAD TO OPERATE WITHOUT AT LEAST 1 FUNCTIONING AUTOFLT SYS. THE CAPT MADE A PA ANNOUNCEMENT; EXPLAINED THE PROB TO THE PAX AND REQUESTED THAT ALL PAX OPERATED ELECTRONIC DEVICES BE TURNED OFF. THE PAX WILLINGLY COMPLIED WITH THE CAPT'S REQUEST. THE PROBS CONTINUED. DURING A SECOND CABIN SWEEP A FLT ATTENDANT OBSERVED A PAX SEATED IN SEAT XXX WEARING HEADPHONES. THE PAX TOLD THE FLT ATTENDANT THAT IT WAS A HEARING AID; AND THAT THE PAX WAS QUITE DEAF WITHOUT IT. THE CAPT DIRECTED THAT THE PAX BE MOVED. HE WAS RESEATED TO ROW YY ON THE R. AS SOON AS THE PAX WAS RESEATED; THE AUTOFLT PROBS STOPPED. THE CREW WROTE UP THE AUTOFLT SYS AND MAINT DID AN EXTENSIVE CHK. NO PROBS WERE FOUND. THE CAPT HAS HAD PREVIOUS EXPERIENCE WITH INTERFERENCE CAUSED WITH PAX OPERATED GAMES WHICH WERE INTERCONNECTED WITH A WIRING HARNESS. HE STATES WIRING ACTS AS AN ANTENNA CAPABLE OF RADIATING AN RF SIGNAL; WHICH IS CAPABLE OF INTERFERING WITH THE ACFT ELECTRONICS. THE CAPT WONDERS WHY THE ACFT MANUFACTURER DOES NOT PROPERLY SHIELD THE ACFT ELECTRONICS TO PREVENT SUCH INTERFERENCE.