AUTOPLT FAILURE CAUSED WDB TO DSND AND EXCEED MAX SPD.

Narrative

AFTER DEPARTING SFO WITH CAPT FLYING; I ENGAGED #1 AUTOPLT IN VERT SPD MODE AT APPROX 10000 FT. SET VERT SPD AT 1000 FPM CLB TO ACCELERATE TO TARGET CLB SPD OF 309 KTS. AT 309 KTS I ENGAGED IAS HOLD FUNCTION OF FLT GUIDANCE SYS AND FLT GUIDANCE SYS ANNUNCIATOR PANEL SO INDICATED. SPD CONTINUED TO BUILD; BUT FLT DIRECTOR PITCH COMMAND BAR OVERLAID THE ACFT INDICE ON THE ADI; INDICATING THAT THE IAS HOLD WAS STILL ENGAGED. AS SPD INCREASED; I TRIED TO REGAIN CTL OF AIRSPD WITH VERT SPD WHEEL. AT THIS POINT; 'VERT SPD' SHOWED IN FLT GUIDANCE SYS ANNUNCIATOR AND FLT DIRECTOR PITCH BAR OVERLAID THE ACFT INDICE. ALTHOUGH AUTOPLT OUT OF TRIM LIGHT DIDN'T ILLUMINATE; I WAS CONCERNED ABOUT DISCONNECTING AUTOPLT AFTER SUDDEN SPD BUILDUP. STABILIZER TRIM INDICATOR DIDN'T SEEM TO BE MOVING. I FEARED EXCESSIVE STRUCTURAL LOAD IF AUTOPLT WAS DISCONNECTED WITH ACFT OUT OF TRIM AT SPD IN EXCESS OF VMO. AS AIRSPD APCHED 390 KTS; I REDUCED THRUST TO NEAR IDLE AND DISCONNECTED AUTOPLT. THERE WAS NO OUT OF TRIM LURCH. NORMAL CLB WAS RESUMED ON AUTOPLT #2 AND SFO MM (SAM) WAS SUBSEQUENTLY NOTIFIED OF ELECTRO- MECHANICAL IRREGULARITY. SUPPLEMENTAL INFO FROM ACN 237134: NONE OF US HEARD THE AIRSPD CLACKER GO OFF AS WE PASSED VMO (BARBERPOLE ALS). MAINT WAS CALLED; THE #1 AUTOPLT WAS TAGGED OTS; AND A LOGBOOK ENTRY WAS MADE. WE WERE CLRED TO CONTINUE WITH THE #1 AUTOPLT INOP. THE REMAINDER OF THE FLT TO KONA AND BACK WAS UNEVENTFUL. THE PROB HERE IS THAT WE WERE SO ENGROSSED IN THE CAUSE OF THE PROB THAT NONE OF US THOUGHT ABOUT THE AIRSPD EXCURSION ABOVE VMO. THE AIR WAS VERY SMOOTH AND WE NEVER FELT ANY 'G' DURING THE ACCELERATION OR THE DECELERATION SO NONE OF US FELT THE OVERSPD WAS A CONCERN. CORRECTIVE ACTION MIGHT BE TO INCLUDE CLEAN OVERSPD PROCS IN THE FOM/FLT HANDBOOK TO INCLUDE THE NECESSITY FOR AN OVERSPD INSPECTION AND NOTIFICATION GIVEN TO MAINT OF THE OVERSPD. WE MAY ALSO WANT TO INCREASE CLACKER VOLUME SO WE HEAR IT BETTER. THE CLACKER WAS WORKING; BUT WAS NOT LOUD ENOUGH TO HEAR WITH ALL SYS AND ENGS RUNNING. WE ALSO NEED AN 'MRM' CODE FOR AN OVERSPD. SUPPLEMENTAL INFO FROM ACN 237135: THE ACFT EXCEEDED THE VMO BY APPROX 40 KIAS.