A B757 CAPT RPTED THAT DURING THE REDEYE 2 ARR INTO LAX THE ACFT SUDDENLY PITCHED OVER CAUSING THE ACFT TO EXCEED MMO-VMO BY 30 KIAS.

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ACFT TYPE B757. 2 INCIDENTS HAPPENED ON THIS FLT. I DOUBT THAT THEY ARE RELATED BUT I MENTION THIS FACT BECAUSE I DON'T WANT THIS POSSIBILITY OVERLOOKED. THIS RPT COVERS ONLY THE SECOND INCIDENT 'NOSE PITCH DOWN AND EXCEEDANCE OF MMO/VMO.' THE FIRST INCIDENT IS THE SUBJECT OF A SEPARATE RPT; TITLED 'UN-NORMAL ACFT SOUND AS THE CTR FUEL TANK RAN DRY.' I WAS THE CAPT OF THIS FLT AND THE PNF. ABC WAS THE COPLT OF THIS FLT AND THE PF. ON DSCNT INTO LAX WE WERE CLRED TO CIVET AND THEN THE REDEYE 2 ARR INTO LAX. WE DSNDED TO OUR CLRNC LIMIT OF FL180 AT CIVET. THE ACFT WAS ON AUTOPLT WITH LNAV AND VNAV ENGAGED. OUR AIRSPD AT THIS TIME WAS COMMANDED BY THE FMS AND WAS ABOUT 10 KTS BELOW THE MMO/VMO POINTER. WE RECEIVED A CLRNC TO DSND VIA THE REDEYE 2 ARR. THE COPLT SELECTED A LOWER ALT; DIALED IN A LOWER AIRSPD; AND DEPLOYED THE SPOILERS. THE ACFT RESPONDED BY LOWERING THE NOSE. TO THIS POINT EVERYTHING WAS NORMAL. THEN THE ACFT REALLY PITCHED DOWN. THE PITCHOVER WAS UNCOMFORTABLE AND VERY NOTICEABLE. THE ACFT ALMOST IMMEDIATELY WENT THROUGH MMO/VMO AND THE COPLT DISENGAGED THE AUTOPLT AND STARTED A RECOVERY. I HAD FLOWN WITH THE COPLT BEFORE AND KNEW HIM TO BE AN EXCELLENT PLT. IN MY ORIGINAL 'ABNORMAL BRIEFING' I HAD BRIEFED THAT IF ANYTHING WENT WRONG; THE PF WOULD CONTINUE TO FLY AND THE PNF WOULD WORK THE CHKLIST. THE NOISE IN THE COCKPIT FROM THE OVERSPD WARNING WAS SO LOUD IT PRECLUDED A PROPER CONVERSATION BTWN US. I OBSERVED THE ACFT ATTITUDE AND SPD AND THE COPLT'S ACTIONS CAREFULLY. HE HAD DISCONNECTED THE AUTOPLT AND WAS IN THE PROCESS OF MAKING A SLOW COORDINATED PULL UP SO AS TO NOT OVERSTRESS THE ACFT. SINCE HIS RESPONSE WAS EXACTLY HOW I WOULD HAVE HANDLED THIS PROB; I ELECTED TO LET HIM CONTINUE HIS RECOVERY AND NOT RISK AN OVER-CTL SIT BY ABRUPTLY TAKING CTL OF THE ACFT AWAY FROM HIM. IN MY OPINION; HE MADE A SMOOTH TEXTBOOK PERFECT NOSE DOWN RECOVERY. THE ACFT REACHED AN INDICATED SPD OF 380 KTS; WHICH WAS ABOUT 30 KTS OVER MMO/VMO. AFTER LNDG WE MADE A LOGBOOK WRITE-UP ABOUT OUR EXCEEDING MMO/VMO.