Narrative:

Radar altimeter inoperative (entered in status book) caused erroneous radar altitude readings and false taws presentation. PF and PNF briefed approach prior to penetration. PNF advised PF he had experienced a false taws pull-up warning on a previous approach to luc. FMS set up correctly. However, the 5000 FMS doesn't display rate of descent cue on vvi to reflect FMS input leg altitudes when navigation sourced to localizer. EFIS map also doesn't show desired altitudes at FMS navigation points. Factors increased task loading. Cincinnati approach requested we keep up speed until FAF. Arrival changed twice during penetration. IMC with light icing, light to moderate turbulence. Required to fly with both hands on yoke. Focus on maintaining aircraft control. Ceiling ragged at about 1400 ft MSL. Commencing approach, PF asked PNF to call out and dial in instrument procedure altitudes, per company SOP (ie, 'talk me through the approach'). Initial vector altitude = 3000 ft MSL. FAF altitude = 2100 ft MSL. MDA = 1240 ft MSL. PF cleared to intercept localizer at 3000 ft, cleared for approach. Once localizer intercepted, PNF called out descent to 2100 ft. PF understood this to be IAF altitude, hands/yoke obstructed FMS map display. Shortly thereafter, but prior to FAF, PNF called out descent to 1240 ft and changed altitude select display to 1240 ft. Crew executed approach check, configured gear down, flaps 20 degrees and began descent. Approach actual FAF, at about 1500 ft, taws 'pull up' command sounded. PNF advised PF to disregard taws command as erroneous. PF noted FMS altitude select display and MDA both showed 1240 ft. PF asked PNF to confirm they had reached the FAF. PNF realized mistake and said 'no, we need to be at 2100 ft.' PF immediately initiated climb to 2100 ft. Cincinnati approach advised their altitude alert had sounded. PF leveled at 2100 ft, continued on course to the FAF. Remainder of approach successfully flown without incident. Lessons learned: 5000 FMS doesn't show same altitude cues as ams 850. No altitudes on map, no vvi cue when FMS not navigation source. PF needs to keep FMS legs page visible to xchk required altitudes at navigation points. Flying IMC approachs without operating 'rad altitude' requires extra attention. Left seat flying requires different xchk because map display is often obscured by yoke unless pilot moves head.

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Original NASA ASRS Text

Title: BE400 FLT CREW DSNDS BELOW APCH SEGMENT ALT ON LOC BACK COURSE APCH.

Narrative: RADAR ALTIMETER INOP (ENTERED IN STATUS BOOK) CAUSED ERRONEOUS RADAR ALT READINGS AND FALSE TAWS PRESENTATION. PF AND PNF BRIEFED APCH PRIOR TO PENETRATION. PNF ADVISED PF HE HAD EXPERIENCED A FALSE TAWS PULL-UP WARNING ON A PREVIOUS APCH TO LUC. FMS SET UP CORRECTLY. HOWEVER, THE 5000 FMS DOESN'T DISPLAY RATE OF DSCNT CUE ON VVI TO REFLECT FMS INPUT LEG ALTS WHEN NAV SOURCED TO LOC. EFIS MAP ALSO DOESN'T SHOW DESIRED ALTS AT FMS NAV POINTS. FACTORS INCREASED TASK LOADING. CINCINNATI APCH REQUESTED WE KEEP UP SPD UNTIL FAF. ARR CHANGED TWICE DURING PENETRATION. IMC WITH LIGHT ICING, LIGHT TO MODERATE TURB. REQUIRED TO FLY WITH BOTH HANDS ON YOKE. FOCUS ON MAINTAINING ACFT CTL. CEILING RAGGED AT ABOUT 1400 FT MSL. COMMENCING APCH, PF ASKED PNF TO CALL OUT AND DIAL IN INST PROC ALTS, PER COMPANY SOP (IE, 'TALK ME THROUGH THE APCH'). INITIAL VECTOR ALT = 3000 FT MSL. FAF ALT = 2100 FT MSL. MDA = 1240 FT MSL. PF CLRED TO INTERCEPT LOC AT 3000 FT, CLRED FOR APCH. ONCE LOC INTERCEPTED, PNF CALLED OUT DSCNT TO 2100 FT. PF UNDERSTOOD THIS TO BE IAF ALT, HANDS/YOKE OBSTRUCTED FMS MAP DISPLAY. SHORTLY THEREAFTER, BUT PRIOR TO FAF, PNF CALLED OUT DSCNT TO 1240 FT AND CHANGED ALT SELECT DISPLAY TO 1240 FT. CREW EXECUTED APCH CHK, CONFIGURED GEAR DOWN, FLAPS 20 DEGS AND BEGAN DSCNT. APCH ACTUAL FAF, AT ABOUT 1500 FT, TAWS 'PULL UP' COMMAND SOUNDED. PNF ADVISED PF TO DISREGARD TAWS COMMAND AS ERRONEOUS. PF NOTED FMS ALT SELECT DISPLAY AND MDA BOTH SHOWED 1240 FT. PF ASKED PNF TO CONFIRM THEY HAD REACHED THE FAF. PNF REALIZED MISTAKE AND SAID 'NO, WE NEED TO BE AT 2100 FT.' PF IMMEDIATELY INITIATED CLB TO 2100 FT. CINCINNATI APCH ADVISED THEIR ALT ALERT HAD SOUNDED. PF LEVELED AT 2100 FT, CONTINUED ON COURSE TO THE FAF. REMAINDER OF APCH SUCCESSFULLY FLOWN WITHOUT INCIDENT. LESSONS LEARNED: 5000 FMS DOESN'T SHOW SAME ALT CUES AS AMS 850. NO ALTS ON MAP, NO VVI CUE WHEN FMS NOT NAV SOURCE. PF NEEDS TO KEEP FMS LEGS PAGE VISIBLE TO XCHK REQUIRED ALTS AT NAV POINTS. FLYING IMC APCHS WITHOUT OPERATING 'RAD ALT' REQUIRES EXTRA ATTN. L SEAT FLYING REQUIRES DIFFERENT XCHK BECAUSE MAP DISPLAY IS OFTEN OBSCURED BY YOKE UNLESS PLT MOVES HEAD.

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.