BE36 PLT HAS THROTTLE VERNIER PROBS AND DSNDS BELOW ASSIGNED ALT WHILE CONDUCTING AN APCH TO VGT UNDER L30 CTL.

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I WAS ON AN IFR FLT PLAN FROM EL PASO INTL. I WAS GIVEN A VECTOR TO FLY HDG 270 DEGS AT 6000 FT. THIS VECTOR TOOK ME JUST S OF THE SOUTHERN BOUNDARY OF MCCARRAN FIELD. WHEN I FIRST CALLED APCH SE OF MCCARRAN; THEY SAID I WAS GARBLED. I REPEATED MY XMISSION AND THEY ACKNOWLEDGED. I RESPONDED TO THE VECTOR AND ALT. A SHORT TIME LATER; APCH SAID 'I NEED YOU TO ACKNOWLEDGE MY XMISSIONS.' THIS PUZZLED ME; SINCE I HAD HEARD NONE. I ACKNOWLEDGED THIS. I WAS THEN TOLD ABOUT TFC AT 2 O'CLOCK POS; CLBING; A B767 (I WAS ON HDG 270 DEGS). I LOOKED AND SAID 'LOOKING.' I DID NOT SEE THE TFC. I KEPT LOOKING. THEN I HEARD CONVERSATION FROM SOMEONE (I AM NOT SURE WHO) SAID 'WE GOT AN RA.' I DO NOT KNOW WHO THIS CAME FROM. NOT SURE IF IT WAS THE B767 OR SOMEONE ELSE. AT ANY RATE; THERE WAS SOME CONVERSATION ABOUT THE RA BTWN ATC AND SOME ACFT. THEN I WAS TOLD TO TURN TO 360 DEG HDG AND EXPECT VISUAL APCH TO RWY 30 AT NORTH LAS VEGAS. I ACKNOWLEDGED. I TURNED AND BEGAN TO THROTTLE BACK FOR DSCNT (I WAS AT 6000 FT AND FIELD ELEVATION WAS ABOUT 2200 FT. I WAS 5-6 MI S). AT THAT POINT MY THROTTLE VERNIER RETENTION SCREW UNTHREADED; POPPING THE SPRING-LOADED VERNIER CTL. THE THROTTLE MOVED TO FULL PWR; AND I HAD TO MAINTAIN TENSION BY HOLDING THE THROTTLE AND PULLING BACK (COULD NOT LET IT GO; AS IT MOVED QUICKLY TO FULL PWR). I HAD TO USE ONE HAND TO KEEP THE THROTTLE RETARDED; SWITCHING BACK AND FORTH TO USE THE CTLS; PUT FLAPS DOWN TO APCH; AND TO LOWER THE GEAR (WAS HIGH CLOSE IN). BTWN DISTR AND COMMOTION; I DID ALLOW A DSCNT TO BEGIN. THINGS STABILIZED (GEAR DOWN AND APCH FLAPS; THROTTLE STEADY WITH HAND TENSION); AND I ASKED APCH CTL 'PLEASE CONFIRM MY ALT RESTR.' THE VOICE SAID 'YOU WERE NOT CLRED FOR THE VISUAL APCH; ONLY TO EXPECT THE VISUAL APCH.' I SAID 'ROGER' AND BEGAN A CLB FROM ABOUT 5400 FT BACK TO 6000 FT. I HAD CLBED ABOUT 100-200 FT AND ANOTHER VOICE CAME ON AND SAID 'YOU ARE CLRED FOR THE VISUAL APCH TO RWY 30 NORTH LAS VEGAS.' I SAID 'ROGER.' THAT SAME PERSON THEN TOLD ME TO STAY ON A NORTHERLY HDG (I WAS GOING TOO FAR E) AS I MADE THE APCH. I LANDED UNEVENTFULLY; HAVING TO HOLD THE THROTTLE RETARDED UNTIL SHUTDOWN. I PARKED AT THE FBO. I ASKED THE PERSON WHO PARKED ME FOR A PHILLIPS SCREWDRIVER; FOUND THE VERNIER CAP; SPRING; AND SCREW AND REPAIRED THE THROTTLE CABLE. IN RETROSPECT; I WAS CHAGRINED BY THE ANNOUNCEMENT THAT I HAD A GARBLED XMISSION AFTER HRS AND HRS OF NO PROB THAT DAY. I WAS CHAGRINED WHEN I WAS TOLD 'I NEED TO KNOW IF YOU ARE WITH ME' (I AM NOT SURE OF THE EXACT WORDS) WHEN I WAS LISTENING INTENTLY. I WAS CONCERNED ABOUT THE RA ANNOUNCEMENT AND THE COMMOTION SORTING IT OUT AND WONDERING IF IT WAS THE B767 THAT I NEVER SAW. I WAS FURTHER COMPROMISED WHEN AT THAT MOMENT THE VERNIER LET GO. NONETHELESS; I MUST ACKNOWLEDGE THAT I WAS INDEED NOT GIVEN A CLRNC FOR VISUAL APCH. I KNOW THAT 'EXPECT VISUAL APCH' DOES NOT MEAN 'CLRED FOR VISUAL APCH.' IN ALL THE CONFUSION BTWN MY DOUBTS ABOUT APCH HEARING ME; ABOUT THE RA; AND THE THROTTLE COMMOTION; I INDEED ALLOWED A DSCNT. SOMETHING DID NOT SEEM RIGHT; WHICH PROMPTED ME TO ASK ABOUT ALT CONFIRMATION WHEN I WAS AT ABOUT 5400 FT. THAT IS WHEN I WS TOLD I HAD NOT BEEN CLRED. I SHOULD HAVE DONE THE FOLLOWING: ASKED IF I WAS BEING RECEIVED LOUD AND CLR. ASKED IF THE RA PERTAINED TO ME AND THE B767. ANNOUNCED MY THROTTLE PROB. NOT DSNDED BELOW 6000 FT AND THEN ASKED ABOUT CONFIRMATION; BUT STAYED AT 6000 FT UNTIL I KNEW. THE COMMOTION DISTR ME.