AN MD90 FO; PF; ENTERS THE WRONG ALT INTO THE ALT ALERTER AND THE ACFT DSNDS THROUGH ITS ASSIGNED ALT OF 15000 FT NEAR SLC; UT.

Narrative

WE WERE RETURNING TO SLC FROM PHX WHEN CTR SAID THEY WERE TURNING THE ARPT AROUND. OUR NEW CLRNC WAS DIRECT FFU; DIRECT SLC. MY FO PROGRAMMED THE RTE AND WE REALIZED IT WOULD TAKE US THROUGH AN AREA OF NUMEROUS TOWERING CUMULUS CLOUDS. WE WERE GIVEN A CLRNC TO CROSS 20 DME OUT OF FFU AT 15000 FT; 250 KTS; ALTIMETER 30.06; WHICH I WROTE DOWN AND READ BACK CORRECTLY. I GOT CLRNC TO DEVIATE L AND R OF COURSE AND MY FO PROGRAMMED THE FIX AND RESTR IN THE FMS. WE THEN GOT A RESTR TO SLOW TO 270 KTS. MY FO HAD INCORRECTLY PROGRAMMED 12000 FT INSTEAD OF 15000 FT. HE PUT 12000 FT IN THE ALT WINDOW (AND I CONFIRMED IT). WE HAD ALSO BEEN UPLINKED WITH AN ALTERNATE AND FUEL BURN NUMBERS FROM OUR DISPATCHER. WE RECEIVED GATE CONNECTIONS WHICH WE PASSED TO THE FLT ATTENDANTS; ALONG WITH BRIEFING AN APCH TO THE NEW RWY; RAN A DSCNT CHKLIST; ETC. WE HAD BEEN CRUISING AT 31000 FT ALL SET AND WITHIN A 5-10 MIN PERIOD IT HAD GOTTEN REAL BUSY WITH ONLY 2 PLTS. WE WERE CONCERNED THAT WE MIGHT NOT GET DOWN; SO WE HAD OUT FULL FLT SPOILERS. SO MANY NUMBERS; SO LITTLE TIME. FROM THE TIME HE HAD INCORRECTLY TYPED 12000 FT; WE WERE BOTH SURE THAT WAS WHERE WE WANTED TO GO. ALL THE WHILE THE CORRECT 15000 FT WAS WRITTEN RIGHT IN FRONT OF ME ON MY SCRATCH PAD. CTR ASKED OUR ALT AND I SAID; 'PASSING 12700 FT FOR 12000 FT.' HE THEN SAID WE WERE CLRED TO 15000 FT. I ASKED IF HE WANTED US TO CLB BACK TO 15000 FT. HE SAID; 'NO STAY AT 12000 FT.' NO TFC CONFLICTS. NO TERRAIN CONFLICTS. TWO VERY HUMBLE PLTS.