CPR C560 DSNDS BELOW ASSIGNED ALT TOWARDS OPPOSITE DIRECTION TFC. FO; PF IN L SEAT HAD CHANGED THE ALT SELECT FROM FL310 TO FL290 DURING DSCNT WHEN HE HEARD TFC RPTED AT FL290. PIC WAS BUSY WITH ATIS AND LNDG DATA.

Narrative

I WAS FLYING IN THE R SEAT; ALLOWING ONE OF OUR COPLTS TO GET SOME L SEAT TIME. THIS WAS A DEADHEAD LEG FROM 5T6 TO LGB FOR MAINT. WE WERE GIVEN A DSCNT FROM FL370 TO FL310. I CONDUCTED THE FIRST PART OF THE DSCNT CHKLIST; AND CONFIRMED THE NEW ALT; AND SET THE ALT SELECTOR TO FL310. WE BEGAN THE DSCNT USING THE AUTOPLT. I BEGAN TO PREPARE THE LNDG DATA; WHICH I WAS BASING ON THE CURRENT LGB ATIS. ZLA CALLED TFC OPPOSITE DIRECTION AT FL290 AND SAID WE WOULD BE GIVEN LOWER WHEN WE CLRED THE TFC. I RESPONDED TO ZLA THAT I DID NOT HAVE THE TFC. I CONTINUED TO COMPUTE LNDG DATA FOR THE PF. AS I LOOKED UP THE NEXT TIME; WE WERE DSNDING THROUGH FL310. I IMMEDIATELY TOOK CORRECTIVE ACTION; BUT WE HAD DSNDED TO FL307. THE CTLR GAVE US A COMMAND TO CLB IMMEDIATELY; WHICH WE HAD ALREADY DONE; BUT WE BUSTED ALT ENOUGH TO SET OFF HIS ALERT; I AM SURE. AFTER I REGAINED THE ALT AND SET THE AUTOPLT UP; I NOTICED THE ALT SELECT WAS AT FL290. I ASKED THE OTHER PLT WHY THE ALT SELECT WAS AT FL290; AND HE SAID HE HAD RESET IT FROM FL310 TO FL290. THE COPLT HEARD THE CTLR CALL TFC AT FL290; AND THOUGHT HE SAID DSND TO FL290. THE OTHER PLT FAILED TO CONFIRM THE NEW ALT WITH ME PRIOR TO MAKING THE CHANGE. OUR PROC REQUIRED CONFIRMATION ON ALL CLRNCS BY BOTH PLTS.