Narrative:

Our aircraft was given clearance to cross somto intersection at 13000 ft, no speed restr. Descent was begun according to vertical guidance planning information generated by the aircraft (airbus a- 320). Descent was begun from 26000 ft. Sometime during the course of descent, nearing 15000 ft, the vertical speed mode assumed control of the aircraft's vertical descent plan and caused it to go off profile on the high side, such that the crossing restr would not be made unless pilot intervention had been made. We discovered the error nearing 14000 ft, at approximately 2 mi from somto intersection. Upon attempting to correct the descent profile, we were queried by approach control as to whether we would make the crossing restr. We actually crossed somto intersection about 500 ft high. No other controller interaction was required at the time, and we weren't aware nor made aware of any conflicting traffic in our immediate (TCASII) vicinity. This problem underscores the need to constantly monitor the progression of the aircraft, especially when in the managed navigation (computer controled versus pilot controled) mode. At the time of the incident I was preparing to make a PA to the passenger, with destination WX, etc. This chore should have been assumed by the PNF, but on this particular trip it was briefed that the PF would make the PA announcements.

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Original NASA ASRS Text

Title: XING ALT RESTR NOT MET. ALT UNDERSHOOT.

Narrative: OUR ACFT WAS GIVEN CLRNC TO CROSS SOMTO INTXN AT 13000 FT, NO SPD RESTR. DSCNT WAS BEGUN ACCORDING TO VERT GUIDANCE PLANNING INFO GENERATED BY THE ACFT (AIRBUS A- 320). DSCNT WAS BEGUN FROM 26000 FT. SOMETIME DURING THE COURSE OF DSCNT, NEARING 15000 FT, THE VERT SPD MODE ASSUMED CTL OF THE ACFT'S VERT DSCNT PLAN AND CAUSED IT TO GO OFF PROFILE ON THE HIGH SIDE, SUCH THAT THE XING RESTR WOULD NOT BE MADE UNLESS PLT INTERVENTION HAD BEEN MADE. WE DISCOVERED THE ERROR NEARING 14000 FT, AT APPROX 2 MI FROM SOMTO INTXN. UPON ATTEMPTING TO CORRECT THE DSCNT PROFILE, WE WERE QUERIED BY APCH CTL AS TO WHETHER WE WOULD MAKE THE XING RESTR. WE ACTUALLY CROSSED SOMTO INTXN ABOUT 500 FT HIGH. NO OTHER CTLR INTERACTION WAS REQUIRED AT THE TIME, AND WE WEREN'T AWARE NOR MADE AWARE OF ANY CONFLICTING TFC IN OUR IMMEDIATE (TCASII) VICINITY. THIS PROB UNDERSCORES THE NEED TO CONSTANTLY MONITOR THE PROGRESSION OF THE ACFT, ESPECIALLY WHEN IN THE MANAGED NAV (COMPUTER CTLED VERSUS PLT CTLED) MODE. AT THE TIME OF THE INCIDENT I WAS PREPARING TO MAKE A PA TO THE PAX, WITH DEST WX, ETC. THIS CHORE SHOULD HAVE BEEN ASSUMED BY THE PNF, BUT ON THIS PARTICULAR TRIP IT WAS BRIEFED THAT THE PF WOULD MAKE THE PA ANNOUNCEMENTS.

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.