A319 FLT CREW ON GRNPA RNAV STAR TO LAS LOSES ALT RESTRAINTS IN THE FMS WHEN PROGRAMMING FOR A RWY CHANGE. ALT AND SPD DEVS RESULT.

Narrative

ON THE GRNPA 1 ARR INTO LAS OUR INITIAL CLRNC WAS TO CROSS LUXOR AT 12000 FT AND 250 KTS. THE CONSTRAINTS FOR THE ARR HAD BEEN VERIFIED IN THE BOX. NEXT; WE RECEIVED THE CLRNC TO DSND VIA THE ARR. UPON RECEIVING THIS CLRNC WE SET 8000 FT IN THE ALT SELECTOR AND CONTINUED THE DSCNT IN A MANAGED MODE. DURING THE DSCNT; PRIOR TO LUXOR; WE WERE TOLD TO EXPECT A VISUAL TO RWY 19R. THE BOX WAS PROGRAMMED FOR LNDG ON RWY 25L. WHILE REPROGRAMMING THE BOX FOR RWY 19R THE ALT AND SPD CONSTRAINTS DROPPED OUT OF THE BOX AND REVERTED TO OPEN DSCNT AND SELECTED SPD. BEFORE WE CAUGHT IT; WE WERE AT 10500 FT AND 300 KTS AT LUXOR. WE MADE THE CORRECTION TO CROSS GRNPA AT 11000 FT; STILL SLOWING ON THE SPD. THE NEXT CLRNC WE RECEIVED WAS DIRECT TRROP INTXN DOWN TO 8000 FT WHICH WAS ACCOMPLISHED AS DIRECTED. NO COMMENT WAS MADE BY ATC REGARDING OUR DEV. THE PROB WAS 2 PLTS TRYING TO REPROGRAM THE BOX INSTEAD OF 1 PLT FLYING AND 1 PLT PROGRAMMING THE BOX DURING A CRITICAL PHASE OF FLT. I BELIEVE A PROCEDURAL CHANGE SHOULD TAKE PLACE AT OUR AIRLINE. THE CURRENT SOP IS THE PF PROGRAMS THE BOX IF THE AIRPLANE IS ON AUTOPLT. I THINK THE PNF SHOULD ALWAYS BE THE ONE PROGRAMMING THE BOX SO THE PF CAN DO JUST THAT -- FLY THE AIRPLANE AND NOT BE 'HEAD DOWN' PROGRAMMING THE BOX. SUPPLEMENTAL INFO FROM ACN 692994: AT THIS POINT I ASKED WHAT HAPPENED AND APPARENTLY WITHOUT ADVISING ME THE FO HAD ELECTED TO ACTIVATE THE SECONDARY FLT PLAN IN THE MCDU WHICH HAD BEEN PROGRAMMED BY THE FO FOR RWY 19R BUT APPARENTLY WITHOUT THE GRNPA 1 ARR AND THUS WHEN THE FO ACTIVATED THE SECONDARY FLT PLAN ALL LATERAL AND VERT GUIDANCE WAS LOST.