ADVANCED TECHNOLOGY LGT OVERSHOT ALT IN AUTOMATIC MODE.

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THIS ACFT LGT IS EQUIPPED WITH THE LATEST AND GREATEST (ALMOST) FLT GUIDANCE/AUTOPLT SYSTEMS AVAILABLE. FORTUNATELY I DON'T BELIEVE ANYTHING IS FOOLPROOF. WE HAD BEEN CLRED FROM 310 TO 350 WHICH WE SET INTO THE ALT WINDOW. THE AUTOPLT WAS ALREADY HOOKED UP SO THE COMMAND TO CLIMB WAS MADE AFTER THE ALT OF 350 WAS SET INTO THE WINDOW. NORMAL (BY OUR REQUIRED PROCEDURES) ALT CALLOUTS WERE MADE. AT APPROX 34800' WE BOTH REALIZED THAT PROPER ANNUNCIATION 'ALT CAP' WAS NOT BEING DISPLAYED SOON ENOUGH FOR OUR RATE OF CLIMB. THE CAPT QUICKLY DISCONNECTED THE AUTOPLT AND AUTOTHROTTLES AND LEVELED THE ACFT. WE OVERSHOT 350 BY ABOUT 200-300' AT THE VERY MOST THANKS TO ALL COCKPIT MEMBERS' VIGILANCE. WE HAD A JUMP SEATER WHO ALSO SAW THE PROBLEM DEVELOP. THIS ACFT AND ITS ELECTRONIC WONDERMENT IS A FINE MACHINE AND IT IS ABSOLUTELY UNDER NO CIRCUMSTANCES SUPPOSED TO VIOLATE ALT SET IN THE WINDOW DURING THIS TYPE OF FLT CONDITION. (CRUISE CLIMB OR DESCENT NOT ON AN ILS) THIS ACFT CONTINUES TO EXHIBIT BEWILDERING ELECTRONIC IDIOSYNCRASIES SUCH AS FALSE MALFUNCTION MESSAGES OF MANY VARIETIES. THIS ALT PROBLEM TURNS OUT TO BE MORE COMMON THAN I THOUGHT AT LEAST THREE OTHER PLTS HAVE HAD IT HAPPEN TO AN ALT ORAL TONE PRIOR TO THE SELECTED ALT BEING REACHED NOT AFTER YOU'VE BROKEN THROUGH BY APPROX 300'! A MAINT WRITEUP WAS MADE. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING INFORMATION: SINCE SENDING REPORT; RPTR HAS TALKED TO AT LEAST 10 OTHER PLTS AND ALL HAVE HAD ALT BUSTS. IN THIS INCIDENT THE FMC WAS IN THE FLC; FLT LEVEL CHANGE; MODE BUT ALT BUSTS ARE ALSO HAPPENING WITH THE FMC IN THE V-NAV; VERTICAL NAVIGATION; MODE. THE NEW ALT WAS IN BOTH THE ALT SELECT ON THE MODE CTL PANEL AND HAD BEEN ENTERED IN THE FMC AND ALT ARM WAS ANNUCIATED BUT THE SYSTEM DID NOT CHANGE TO ALT CAPTURE. RPTR HAD ALSO DISCUSSED PROBLEM WITH INSTRUCTOR PLT AND COMPANY IS AWARE OF THE PROBLEM. THE PROBLEM APPEARS TO HAVE SURFACED IN THE LAST YEAR AND ONE HALF AS THE ACFT GET OLDER AS IT WAS NOT A PROBLEM IN FIRST COUPLE YEARS OF OPERATION. RPTR WONDERS IF HEAT AND AGE ARE CAUSING BREAKDOWN IN THE SYSTEM OR SOFTWARE AS THEY ARE GETTING MORE SPURIOUS MESSAGES POSSIBLY FROM THE MULTIPLEXING WIRING SYSTEM. TO DATE MANUFACTURER HAS FAILED TO ACKNOWLEDGE PROBLEM WITH SYSTEM. SYSTEM'S FORMER PERFORMANCE HAS CAUSED FLT CREWS TO RELAX VIGILANCE BUT CONFIDENCE BASE IS NOW BEING ERODED AND MORE ARE HANDFLYING IN CLIMB AND DESCENT TO KEEP ATTN ON SYSTEM. RPTR ALSO FEELS STRONGLY THAT AURAL WARNING SHOULD BE RETURNED TO ALT ALERT SYSTEM 300' BEFORE ALT AS ON OLDER ACFT.