MD80 ACFT DURING DSCNT FAILED TO LEVEL AT NEWLY ASSIGNED ALT AND CAME IN CONFLICT WITH ANOTHER ACFT WHICH WAS CLBING AND GOT TCASII WARNING. CAPT WAS FLYING AND FO WAS OFF FREQ COM WITH HIS ACR. ATC ISSUED A NEW ALT CLRNC TO RPTR WHO READ IT BACK PROPERLY; BUT FAILED TO LEVEL UNTIL ATC INTERVENED. THOUGH RPTR CAPT SAW TCASII TARGET; HE DIDN'T SAY ANYTHING TO ATC.

Narrative

ON A FLT FROM ONT TO PDX WE WERE DSNDING FROM CRUISE ALT OF FL310 WITH A PLT'S DISCRETION CLRNC TO FL240. PASSING FL260 A TARGET APPEARED ON THE TCASII AT 2 O'CLOCK 6 NM AND 1800 FT; SHORTLY FOLLOWED BY AN RA COMMAND TO CLB. WE WERE DSNDING AT 2500 FPM IN PERFORMANCE MODE ON THE FLT GUIDANCE. I WENT TO THE VERT SPD MODE TO CLB. STILL DSNDING WITH THE ACFT JUST STARTING TO RESPOND TO THE VERT SPD CLB; ZSE ASKED OUR ALT. I RESPONDED 'FL250 FOR FL240' WHILE FOCUSING ALL MY ATTN ON OUR ACFT AND WATCHING THE TARGET ACFT ON THE TCASII. I DIDN'T SAY ANYTHING TO ZSE AT THAT TIME ABOUT THE RA BECAUSE I WAS PUTTING ALL MY ATTN ON FLYING OUR ACFT AND WATCHING THE TCASII. ZSE THEN RECLRED US TO FL260 WHICH I ACKNOWLEDGED THEN LEVELED AT FL260. THE TARGET ACFT PASSED AT 700 FT AND 2 NM OFF OUR R SIDE. ZSE THEN CLRED US TO FL240; THEN 10000 FT AND SWITCHED CTR FREQS. THEY ADVISED US OF A PHONE NUMBER TO CALL FOR A POSSIBLE PLTDEV. UPON CALLING THEM ON THE TELEPHONE THEY APPARENTLY ARE SAYING WE WERE CLRED TO FL260 BEFORE WE WERE AT FL250 BECAUSE AN ACFT CLBING OUT HAD REQUESTED FL250. THAT IS NOT MY RECOLLECTION OF THE SEQUENCE OF EVENTS. TO THE BEST I CAN RECALL; WE WERE CLRED TO FL260 ONLY AFTER PASSING FL250 AND AFTER THE RA. HUMAN PERFORMANCE CONSIDERATIONS: IN THE SAME SIT AGAIN I WOULD LIKE TO RESPOND TO THE RA EVEN QUICKER THAN I DID. THIS WAS THE FIRST ONE I HAD GOTTEN AT A HIGH ALT; CTR DID NOT ADVISE US OF THE TFC AS THEY USUALLY DO AND I HAD NOT HEARD THE TARGET ACFT ON CTR FREQ (HE WAS APPARENTLY ON ANOTHER FREQ). THE RA WAS A COMPLETE AND UNEXPECTED SURPRISE TO ME AND IT PROBABLY TOOK ME A COUPLE OF SECONDS TO REACT TO IT. THE FO WAS OFF CTR FREQ CALLING THE COMPANY ABOUT SEVERAL PAX SITS. WE WERE ABOUT 30 MINS LATE AND THE FO WAS OFF CTR FREQ LONGER THAN NORMAL. NORMALLY BOTH PLTS ARE ON CTR FREQ FOR THE DSCNT FROM THE BEGINNING OF DSCNT ON DOWN. CONSEQUENTLY HE WASN'T ABLE TO ASSIST IN CTR COM OR RECALLING THE SEQUENCE OF EVENTS. THE ENTIRE EVENT WAS ONLY A FEW SECONDS; THEN IT WAS OVER. PREVENTIVE MEASURES: PLTS (ME) RESPONDING QUICKER TO RA'S. CTR'S CALLING OUT TFC WHICH IS TO PASSING WITHIN 1000 FT AT ALT (WHICH THEY NORMALLY DO). PNF CALLING COMPANY BEFORE THE DSCNT STARTS IF AT ALL POSSIBLE.