ALTDEV XING RESTR NOT MET. VNAV CONSTRAINT DROPPED OUT WHEN INSERTING NEW CONSTRAINT.

Narrative

RECEIVED CLRNC FROM ZJX TO DSND FROM FL370 TO CROSS CLAWZ INTXN AT FL270. ENTERED XING RESTR IN MCDU; SELECTED CONSTRAINT PUSH BUTTON AND SET FL270 IN ALT WINDOW; THEN PUSHED LEVEL CHANGE KNOB FOR A VNAV DSCNT. EVERYTHING LOOKED NORMAL AT THIS POINT AND WE SHOULD HAVE INTERCEPTED THE DSCNT PROFILE IN ABOUT 2-3 MIN. WENT BACK TO MCDU AND FOUND THE STAR APCH PLATE TO INPUT LEESE XING RESTR. SIDE NOTE: FLT ATTENDANT CAME INTO THE COCKPIT JUST ABOUT THIS TIME TO ASK ABOUT SOMETHING. THE MCDU DROPPED THE CLAWZ XING RESTR AND WOULD NOT ALLOW IT TO BE REINSERTED. GAVE AN ERROR MESSAGE THAT THE INPUT WAS OUTSIDE OF THE CORRECT RANGE. AT THIS POINT; WE WENT TO OPEN DSCNT USING SPEED BRAKES IN AN ATTEMPT TO MAKE THE XING RESTR. WAS UNABLE TO MAKE FL270 UNTIL 5-6 NM PAST CLAWZ DUE IN PART TO AN INCREASE IN THE TAILWIND OF AN ADDITIONAL 25 KTS (105 VS 80-85). CROSSED CLAWZ AT FL300 AND WAS UNABLE TO CONTACT CTR TO ADVISE AS FREQ HAD BEEN QUITE BUSY WITH 4-5 OTHER ACFT. NO KNOWN CONFLICTS; NO COMMENT FROM ZJX. CHANGED FREQ A BIT LATER. THE AIRBUS STILL DOES VARIOUS THINGS WHICH ARE NOT LOGICAL NOR EASILY EXPLAINED. IT SEEMS AS PROBS ARE CORRECTED IN THE SOFTWARE OTHERS ARE CREATED AND SOME PROBS THAT SUPPOSEDLY HAVE BEEN FIXED STILL EXIST UNDER CERTAIN CIRCUMSTANCES. CONSTANT VIGILANCE SEEMS TO BE THE ONLY ANSWER.