Narrative:

After vectors off filed route a new STAR was issued. ATC requested a crossing of the 50 DME of bpr at FL240. Descent from FL350 was begun while the first officer did the required FMS entries. Encountering difficulty with the format for entry my attention was diverted to explain the format for FMS to the first officer. Upon completion of the entry the descent information was slow being displayed (an unfortunate characteristic of the widebody transport aircraft FMS). Meanwhile, mental calculations indicated the crossing restriction could not be made but repeated attempts to notify ATC of the problem was rendered impossible by frequency congestion. When ATC was finally contacted, we were instructed to continue descent to a lower altitude and told the crossing was of no consequence. While all seemed to end well, I was very unsettled by the event, in that such crossing restrictions I try to lead by a comfortable margin. My own inexperience with this aircraft simply did not alert me to the difficulty in complying with the clearance when first issued and the FMS format problem encountered by the first officer are all too common on this aircraft in that the FMS is less 'user friendly' than my previous aircraft, the widebody transport/large transport aircraft. I have incorporated a procedure that all climbs and dscnts be conducted with raw data for the 'on route.' vors will be continually displayed to avoid this problem. The FMS on the widebody transport aircraft does not normally use on route vors for position updating of the FMS so it becomes a crew function to override automatic tuning in order to be prepared for such 'pop-up' clrncs. I have contacted my chief pilot advising him of the problem and my suggested procedural fix. In addition, I advised that training be advised to suggest this procedure be included in the training syllabus, for raw data display to top of climb and from beginning of descent.

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Original NASA ASRS Text

Title: FLC OF WDB ACFT UNDERSHOT A DSCNT ALT DUE THE COMPUTER FMS BEING SLOW TO RESPOND TO THE NEW DATA INPUT.

Narrative: AFTER VECTORS OFF FILED RTE A NEW STAR WAS ISSUED. ATC REQUESTED A XING OF THE 50 DME OF BPR AT FL240. DSCNT FROM FL350 WAS BEGUN WHILE THE FO DID THE REQUIRED FMS ENTRIES. ENCOUNTERING DIFFICULTY WITH THE FORMAT FOR ENTRY MY ATTN WAS DIVERTED TO EXPLAIN THE FORMAT FOR FMS TO THE FO. UPON COMPLETION OF THE ENTRY THE DSCNT INFO WAS SLOW BEING DISPLAYED (AN UNFORTUNATE CHARACTERISTIC OF THE WDB ACFT FMS). MEANWHILE, MENTAL CALCULATIONS INDICATED THE XING RESTRICTION COULD NOT BE MADE BUT REPEATED ATTEMPTS TO NOTIFY ATC OF THE PROBLEM WAS RENDERED IMPOSSIBLE BY FREQ CONGESTION. WHEN ATC WAS FINALLY CONTACTED, WE WERE INSTRUCTED TO CONTINUE DSCNT TO A LOWER ALT AND TOLD THE XING WAS OF NO CONSEQUENCE. WHILE ALL SEEMED TO END WELL, I WAS VERY UNSETTLED BY THE EVENT, IN THAT SUCH XING RESTRICTIONS I TRY TO LEAD BY A COMFORTABLE MARGIN. MY OWN INEXPERIENCE WITH THIS ACFT SIMPLY DID NOT ALERT ME TO THE DIFFICULTY IN COMPLYING WITH THE CLRNC WHEN FIRST ISSUED AND THE FMS FORMAT PROBLEM ENCOUNTERED BY THE FO ARE ALL TOO COMMON ON THIS ACFT IN THAT THE FMS IS LESS 'USER FRIENDLY' THAN MY PREVIOUS ACFT, THE WDB/LGT ACFT. I HAVE INCORPORATED A PROC THAT ALL CLBS AND DSCNTS BE CONDUCTED WITH RAW DATA FOR THE 'ON RTE.' VORS WILL BE CONTINUALLY DISPLAYED TO AVOID THIS PROBLEM. THE FMS ON THE WDB ACFT DOES NOT NORMALLY USE ON RTE VORS FOR POS UPDATING OF THE FMS SO IT BECOMES A CREW FUNCTION TO OVERRIDE AUTOMATIC TUNING IN ORDER TO BE PREPARED FOR SUCH 'POP-UP' CLRNCS. I HAVE CONTACTED MY CHIEF PLT ADVISING HIM OF THE PROBLEM AND MY SUGGESTED PROCEDURAL FIX. IN ADDITION, I ADVISED THAT TRAINING BE ADVISED TO SUGGEST THIS PROC BE INCLUDED IN THE TRAINING SYLLABUS, FOR RAW DATA DISPLAY TO TOP OF CLB AND FROM BEGINNING OF DSCNT.

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.