MLG ACFT ON PROFILE DSCNT FLC MISUNDERSTOOD CLRNC AND DSNDED BELOW ALT RESTR. CAPT RPTR WAS OFF ATC FREQ. FO WAS NEW AND MISUNDERSTOOD CLRNC. CAPT ACCEPTED FO INTERP AND DSNDED TOO SOON UNTIL ATC INTERVENED.

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FLT UNEVENTFUL UNTIL ATC CLRNC TO PROCEED DIRECT CIVET AND CLRED CIVET ONE ARR. NEXT ATC CLRNC WAS TO DSND PLT DISCRETION TO FL240. SHORTLY THEREAFTER WAS ANOTHER ATC CLRNC TO DSND TO (NOT REMEMBERED) ALT. SHORT TIME ELAPSED BEFORE ANOTHER ATC CLRNC TO DSND TO 17000 FT. PF; MYSELF; WAS MOMENTARILY NOT MONITORING ATC RADIO FREQ; COMMUNICATING WITH FLT ATTENDANTS ABOUT POSSIBLE MODERATE TURB IN LAX AREA. PNF RECEIVED ATC CLRNC TO PROCEED TO BREMR INTXN (NEXT FIX) AND INTERCEPT ILAX LOC COURSE. PF RETURNED TO MONITORING ATC RADIO FREQ AND PNF STATED CLRNC TO PROCEED TO BREMR FOR APCH. PF INTERPRETED THAT TO MEAN; CLRED TO BREMR AND FLY REST OF CIVET ONE ARR. HE TOLD PNF TO RESET MCP FLT ALT TO 12000 FT. DSNDING TO 14000 FT; ATC ASKED FLT WHAT THEIR ALT WAS; REPLY WAS PASSING 14500 FT GOING TO 12000 FT. ATC DIRECTED LEVEL OFF AT 14000 FT. PF COMPLIED AND REMAINDER OF FLT (APCH AND LNDG) UNEVENTFUL EXCEPT SOCAL APCH SWITCHED APCH FROM RWY 25L TO RWY 24R AFTER ARNES INTXN. CAPT WAS INFORMED TO CONTACT LOS ANGELES ATC MGR AFTER PARKING AT GATE. HE WAS TOLD THAT POSSIBLE ALTDEV RPT WOULD BE FILED. HE WAS CONTACTED LATER THAT DAY BY AN ATC REPRESENTATIVE AND TOLD THAT TAPES WERE REVIEWED AND RPT WOULD BE FILED. HUMAN PERFORMANCE CONSIDERATIONS: CAPT BELIEVES THAT INITIAL CLRNC FOR APCH COUPLED WITH ANOTHER CLRNC TO A FIX ON THAT APCH AND INTERVENING ALT RESTR (17000 FT) CONFUSED NEW (INEXPERIENCED) FO. AND; BECAUSE CAPT DID NOT HEAR FIRST HAND ATC CLRNC TO BREMR AND INTERCEPT ILAX LOC COURSE; HE ASSUMED FROM FO THAT HE WAS CLRED FOR APCH. THUS HE DSNDED DOWN TO BREMR ALT OF 12000 FT. READ BACK VERBATIM OF ATC CLRNC TO ATC AND TO CAPT BY FO WOULD HAVE PREVENTED POSSIBLE ALTDEV. BOTH ATC AND CAPT WOULD THEN HAVE OPPORTUNITY TO CLARIFY ATC INSTRUCTIONS.