Narrative:

We had been assigned the ILS runway 06 at teb. My first officer and I completed our descent checklist that included an approach briefing. We both caught that there was a mandatory crossing altitude to the fix prior to the final approach fix. On the chart it appeared that this fix would be crossed at the correct altitude if one flew on the GS. The mandatory crossing altitude was 1500 ft MSL. We were already on the localizer when issued our approach clearance of 'descend to 2000 ft cleared ILS 06 approach.' I had decided to allow the airplane to fly the approach in FMS/VNAV mode to the FAF so all altitude restrs would be made, but it automatically goes to short range navigation mode with a stable signal from the localizer/GS. Thinking that I'd cross the mandatory altitude if I simply stayed on the GS, I allowed the autoplt to continue tracking the localizer/GS in short range navigation mode. We crossed the mandatory crossing altitude fix (dandy) at about 1800 ft MSL. Contributing to this deviation: both crew members' failure to detect that dandy's mandatory crossing altitude was not on the GS. My airline backgnd and familiarity with commercial chart profile depiction versus nos (naco - second) profile depictions. Nos (naco - second) profile of dscnts shows one descending line even for step downs. The depiction on the teb ILS 06 shows the altitude profile very close to the GS feather. Other charts avoid confusion by showing each step down graphically with descent and level-offs prior to GS interception.

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Original NASA ASRS Text

Title: ALT CROSSING RESTR NOT MET WHEN ALT UNDERSHOT DURING DSCNT FOR ILS RWY 06 OUTSIDE OF DANDY INTXN, 6 NM SW OF TEB, NJ.

Narrative: WE HAD BEEN ASSIGNED THE ILS RWY 06 AT TEB. MY FO AND I COMPLETED OUR DSCNT CHKLIST THAT INCLUDED AN APCH BRIEFING. WE BOTH CAUGHT THAT THERE WAS A MANDATORY CROSSING ALT TO THE FIX PRIOR TO THE FINAL APCH FIX. ON THE CHART IT APPEARED THAT THIS FIX WOULD BE CROSSED AT THE CORRECT ALT IF ONE FLEW ON THE GS. THE MANDATORY CROSSING ALT WAS 1500 FT MSL. WE WERE ALREADY ON THE LOC WHEN ISSUED OUR APCH CLRNC OF 'DSND TO 2000 FT CLRED ILS 06 APCH.' I HAD DECIDED TO ALLOW THE AIRPLANE TO FLY THE APCH IN FMS/VNAV MODE TO THE FAF SO ALL ALT RESTRS WOULD BE MADE, BUT IT AUTOMATICALLY GOES TO SHORT RANGE NAV MODE WITH A STABLE SIGNAL FROM THE LOC/GS. THINKING THAT I'D CROSS THE MANDATORY ALT IF I SIMPLY STAYED ON THE GS, I ALLOWED THE AUTOPLT TO CONTINUE TRACKING THE LOC/GS IN SHORT RANGE NAV MODE. WE CROSSED THE MANDATORY CROSSING ALT FIX (DANDY) AT ABOUT 1800 FT MSL. CONTRIBUTING TO THIS DEV: BOTH CREW MEMBERS' FAILURE TO DETECT THAT DANDY'S MANDATORY CROSSING ALT WAS NOT ON THE GS. MY AIRLINE BACKGND AND FAMILIARITY WITH COMMERCIAL CHART PROFILE DEPICTION VERSUS NOS (NACO - SEC) PROFILE DEPICTIONS. NOS (NACO - SEC) PROFILE OF DSCNTS SHOWS ONE DSNDING LINE EVEN FOR STEP DOWNS. THE DEPICTION ON THE TEB ILS 06 SHOWS THE ALT PROFILE VERY CLOSE TO THE GS FEATHER. OTHER CHARTS AVOID CONFUSION BY SHOWING EACH STEP DOWN GRAPHICALLY WITH DSCNT AND LEVEL-OFFS PRIOR TO GS INTERCEPTION.

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.