ALT XING RESTR NOT MET BY A320 FLC.

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RECEIVED CLRNC TO CROSS 25 DME W OF ESL VOR AT FL290; LEVEL AT FL330. THIS A320 ACFT SOFTWARE IS UNABLE TO ACCOMMODATE SUCH A CLRNC; SO I SUGGESTED TO CAPT STUDENT IN L SEAT TO PROGRAM THE COMPUTER TO CROSS (ON BUCKO 4 ARR -- FLT WAS KDTW - KDCA) 'BUCKO' AT FL290; 39 DME W OF ESL (IE 14 DME EARLY) SINCE WE WERE SO BUSY PREPARING FOR THE MOUNT VERNON VISUAL APCH TO KDCA RWY 36; AND HE'D NEVER BEEN THERE BEFORE IN ANY CAPACITY AS A PLT. WE WERE SUBSEQUENTLY CLRED DIRECT TO ESL (POS STILL W OF BUCKO) AND THEREFORE DELETED (INADVERTENTLY) OUR PROGRAMMING FOR DSCNT TO FL290. AS WE WERE HANDED OFF TO ZDC (I THINK FROM CLEVELAND) WITH 5 MI TO GO; I REALIZED WE HADN'T STARTED DOWN FROM FL330; AND WOULDN'T MAKE THE RESTR. WHEN CONTACTING ZDC; I TOLD HIM WE WOULD NOT MAKE THE RESTR AND CONFIRMED THE CLRNC (HE SHOWED US 'AT 25 W OF ESL. WE WERE 30 W WHEN I FIRST CHKED ON') I SUGGESTED A 360 DEG TURN BUT HE NEVER ACKNOWLEDGED. IF ATC WOULD USE A NAMED INTXN OR WAYPOINT FOR THESE CLRNCS; THIS WOULD BE FAR LESS OF A PROB. INSTEAD OF 'CROSS 25 W OF ESL AT FL290;' 'CROSS ABCDE AT FL290' AND ALL AIRBUS ACFT COULD BE PROGRAMMED TO DO JUST THAT. IN ANY EVENT; THIS EVENT WAS 'MEA CULPA' -- AND I WILL START DOWN IMMEDIATELY WITH A STUDENT IN THE FUTURE!