UNSTABLE APCH. AUTOTHROTTLES KEPT RE-ENGAGING AFTER BEING DISCONNECTED.

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APPROX 20 DME FROM LAS VOR; ESTABLISHED ON THE RWY 25L LOC AND SLIGHTLY ABOVE THE GS AT 250 KTS; WE WERE CLRED FOR A VISUAL APCH. AT APPROX 17 DME; I DISCONNECTED THE AUTOPLT; DISENGAGED THE AUTOTHROTTLES AND TURNED OFF THE FLT DIRECTOR AND BEGAN TO SLOW TO FLAP SPD. THE ACFT DID NOT WANT TO SLOW AND I DISCOVERED THE AUTOTHROTTLES HAD REENGAGED. I DISCONNECTED THEM AGAIN AND EXTENDED FLAPS AND SPD BRAKES. AT THIS POINT THE SPD BUG WAS AT 180 KTS. GEAR WAS EXTENDED; BUT THE ACFT WAS NOT DSNDING NORMALLY. THE AUTOTHROTTLES HAD ENGAGED AGAIN. AT THIS POINT WE WERE QUITE HIGH ON THE PROFILE AND I REQUESTED AND WAS GIVEN AN S-TURN TO GET BACK ON PROFILE. I AGAIN DISENGAGED THE AUTOTHROTTLES AND KEPT MY HAND ON THE THROTTLES IN CASE THEY CAME ON AGAIN. WE WERE BACK ON PROFILE BY 700 FT AGL AND MADE A NORMAL LNDG. HOWEVER; ALL THE MANEUVERING CLOSE TO LNDG PROMPTED SEVERAL OF THE PAX TO EXPRESS THEIR CONCERNS AS THEY LEFT THE ACFT. IN ADDITION; THE GND CTLR REQUESTED I CALL TRACON. TRACON ASKED IF APCH HAD KEPT ME TOO HIGH BEFORE THE HDOF (WHICH THEY HADN'T) AND REQUESTED THAT IN THE FUTURE I NOTIFY THEM EARLIER; IF POSSIBLE; OF BEING TOO HIGH. NEEDLESS TO SAY; I WAS HIGHLY EMBARRASSED AT HAVING GOTTEN MYSELF INTO THAT SIT; AND I WAS STILL AT A LOSS AS TO WHY THE AUTOTHROTTLES KEPT RE-ENGAGING. THIS WAS ONLY THE SECOND LEG I HAD FLOWN WITH THIS FO. HE HAD FLOWN THE FIRST ONE FROM SFO TO DEN AND WAS AN EXCELLENT PLT BUT TENDED TO WANT TO 'FLY SOLO.' HE WOULD ALWAYS TRY TO DO HIS OWN CDU PROGRAMMING AND MCP CHANGES EVEN WHEN HE WAS HAND FLYING AND AT OTHER TIMES WHEN IT WAS NOT SOP. HE ALSO HAD A TENDENCY TO USE 'VERT SPD' FOR DSCNTS WHEN IT WAS NOT THE MOST APPROPRIATE METHOD. ON MY LEG; HE WOULD MAKE CDU PROGRAMMING CHANGES WITHOUT ASKING ME ABOUT THEM FIRST AND CHANGE MCP ITEMS IN RESPONSE TO ATC INSTRUCTIONS WITHOUT ASKING WHAT MODES I WANTED SET. AFTER REFLECTING ON THIS THAT EVENING; I REALIZED THAT IF THE FO HAD BEEN DOING HIS NORMAL JOB OF TRYING TO HELP ME OUT (WITH HIS FLT DIRECTOR ON); HE MIGHT HAVE BEEN SELECTING ALTS AND MCP MODES WITHOUT CONSULTING ME; WHICH SEEMED TO BE THE ONLY EXPLANATION FOR THE AUTOTHROTTLES CONTINUALLY RE- ENGAGING. I HAVE LEARNED SEVERAL THINGS FROM THIS: 1) HOW EASILY A LAPSE IN SOP CAN CAUSE A CONFUSING PROB. 2) NIP ANY TENDENCY OF YOUR FLYING PARTNER TO 'GO SOLO' IN THE BUD; IT'S BETTER TO RISK INJURING HIS FEELINGS THAN TO GET IN A JAM BECAUSE HE'S TRYING TO HELP WITHOUT COMMUNICATING. (NO SECRETS; NO SURPRISES!) 3) WHEN DSNDING WITH THE AUTOPLT; AUTOTHROTTLES AND FLT DIRECTOR OFF; ALWAYS KEEP 1 HAND ON THE THROTTLES. THAT WAY YOU WILL KNOW INSTANTLY IF THE AUTOTHROTTLES RE-ENGAGE AND BE ABLE TO AVOID ANY PROBS THEY MIGHT CAUSE. 4) IT'S BEEN SAID A HUNDRED TIMES: 'IF YOU'RE UNCOMFORTABLY HIGH; TAKE IT AROUND.' IT'S LESS DISTRESSING TO THE PAX; LESS EMBARRASSING FOR THE CREW AND CAUSES LESS PROBS FOR ATC. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: CAPT RPTR ATTRIBUTES AUTOTHROTTLE RE-ENGAGEMENTS TO THE FO MAKING CHANGES ON THE MCP AND CDU. THE FO WASN'T COMMUNICATING WITH THE CAPT DIDN'T KNOW WHAT HE WAS DOING DURING THE APCH. HOWEVER; RPTR SAID THE AUTOTHROTTLES BEING DISENGAGED WITH THE THROTTLE DISCONNECT BUTTONS DOESN'T DISENGAGE THE ARMING SWITCH WHICH CAN ALLOW THE AUTOTHROTTLES TO RE-ENGAGE. CONSEQUENTLY; IF THE FO SETS MODES; SPDS; ETC; THE AUTOTHROTTLES COULD RE-ENGAGE. CAPT SAID THAT THERE WAS A MAJOR LACK OF COCKPIT RESOURCE MGMNT WITH THE FO.