Narrative:

Flight uneventful until ATC clearance to proceed direct civet and cleared civet one arrival. Next ATC clearance was to descend pilot discretion to FL240. Shortly thereafter was another ATC clearance to descend to (not remembered) altitude. Short time elapsed before another ATC clearance to descend to 17000 ft. PF, myself, was momentarily not monitoring ATC radio frequency, communicating with flight attendants about possible moderate turbulence in lax area. PNF received ATC clearance to proceed to bremr intersection (next fix) and intercept ilax localizer course. PF returned to monitoring ATC radio frequency and PNF stated clearance to proceed to bremr for approach. PF interpreted that to mean, cleared to bremr and fly rest of civet one arrival. He told PNF to reset MCP flight altitude to 12000 ft. Descending to 14000 ft, ATC asked flight what their altitude was, reply was passing 14500 ft going to 12000 ft. ATC directed level off at 14000 ft. PF complied and remainder of flight (approach and landing) uneventful except socal approach switched approach from runway 25L to runway 24R after arnes intersection. Captain was informed to contact los angeles ATC manager after parking at gate. He was told that possible altitude deviation report would be filed. He was contacted later that day by an ATC representative and told that tapes were reviewed and report would be filed. Human performance considerations: captain believes that initial clearance for approach coupled with another clearance to a fix on that approach and intervening altitude restr (17000 ft) confused new (inexperienced) first officer. And, because captain did not hear first hand ATC clearance to bremr and intercept ilax localizer course, he assumed from first officer that he was cleared for approach. Thus he descended down to bremr altitude of 12000 ft. Read back verbatim of ATC clearance to ATC and to captain by first officer would have prevented possible altitude deviation. Both ATC and captain would then have opportunity to clarify ATC instructions.

Google
 

Original NASA ASRS Text

Title: 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.

Narrative: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.