B757-200 CREW HAD AN ALTDEV; AFTER USING AN RNAV APCH TO RWY 29 AT EWR. THE CREW WAS CLRED FOR THE ILS RWY 4L APCH; CIRCLE TO LAND RWY 29.

Narrative

ALTDEV ON APCH. CLRED FOR APCH; ILS RWY 4L; CIRCLE TO LAND RWY 29. FMS HAS RNAV FROM S CIRCLE RWY 29 APCH IN DATABASE; BUT IT IS BASED UPON ILS FIXES ASSOCIATED WITH ILS RWY 4R (PARALLEL RWY). THE APCH WAS THOROUGHLY BRIEFED; ALONG WITH THE FACT THAT BOTH THE ILS RWY 4L AND THE RNAV APCHS COULD NOT BE DISPLAYED ON THE FMS AT THE SAME TIME (DIFFERENT FIX IDENTIFIERS AND UNDERLYING APCHS). BOTH R AND L DME'S WERE TUNED TO THE ILS DME FOR STEP-DOWN FIX IDENT. 'PNF' DISPLAYED APCH WITH ILS IDENTED; PF WAS IN MAP MODE; AND ILS DISPLAYED ON BOTH ADI'S. APCH CLRED ACFT TO MAINTAIN 3000 FT UNTIL ESTABLISHED; CLRED FOR APCH. TURN ONTO FINAL WAS LATE; RESULTING IN SOME OVERSHOOT; ALTHOUGH THE AUTOPLT CAPTURED WITH 40 DEG CORRECTION. PF SWITCHED TO APCH TO VERIFY ESTABLISHMENT ON LOC FOR SITUATIONAL AWARENESS. PF SWITCHED BACK TO NAV; TO DISPLAY BAL OF APCH. STEP-DOWN ALT WAS SELECTED AWAITING STEP-DOWN DME FIX. IN SWITCHING BACK TO NAV; DME REVERTED FROM REMOTE TO MANUAL THEN BACK TO AUTO-TUNING (UNANNUNCIATED). XING DME FIX; NOW TUNED TO THE WRONG DME; STEP-DOWN WAS COMMENCED. ACFT DSNDED APPROX 300 FT BEFORE 'PNF' DETECTED ERROR AND ATC QUERIED ALT. ACFT RETURNED TO CORRECT ALT; AND FINISHED APCH WITHOUT FURTHER EVENT.