B737-400 FLC FAILS TO CHANGE TO TWR FREQ FOR LNDG CLRNC. CREW CITES DISTR WITH A SPD RESTR AND PROX TO OTHER ACFT ON PARALLEL APCH AS THE CAUSE OF FREQ CHANGE MISSED. CREW SAYS; 'NO HDOF GIVEN TO TWR.'

Narrative

SEA APCH CTL CLRED US FOR A VISUAL APCH TO RWY 34L AT SEATAC ARPT FROM RADAR VECTORS ON L DOWNWIND; L BASE. CONCURRENTLY; A B757 WAS APCHING FROM THE E (R BASE; R TURN TO FINAL) FOR A VISUAL APCH TO RWY 34R. THE B757 WAS SLIGHTLY AHEAD OF US IN TURNING FINAL; SO WE WERE INTENT ON MAINTAINING VISUAL CONTACT (AND SEPARATION) WITH THAT ACFT AND LINING UP ON THE VISUAL TRACK FOR RWY 34L. DURING THE TURN TO FINAL; APCH CTL ISSUED US A DME XING SPD RESTR TO COMPLY WITH ON FINAL. OUR CREW BECAME VERY BUSY COMPLYING WITH THE RESTRS; CONFIGURING THE ACFT; MAINTAINING SEPARATION WITH THE PARALLEL B757; AND LISTENING TO OTHER XMISSIONS FROM APCH CTL. AS A CONSEQUENCE; WE NEVER CONFIRMED OUR LNDG CLRNC WITH THE TWR; ALTHOUGH I AM SURE THEY GAVE US A CLRNC TO LAND. ADDITIONALLY; APCH CTL SEEMED VERY BUSY AND NEVER DIRECTED US TO SWITCH RADIO FREQS TO TWR. FAILURE OF THE APCH CTLR TO SWITCH US TO THE TWR AND OUR FAILURE TO CONFIRM LNDG CLRNC SEEMS TO BE A CLASSIC CASE OF TASK OVERLOAD AND DISTR DURING THE FINAL SEGMENT. SUPPLEMENTAL INFO FROM ACN 380346: WE WERE CLRED FOR A VISUAL APCH TO RWY 34L AND TOLD TO MAINTAIN VISUAL SEPARATION FROM A B757 THAT WAS ON VISUAL TO RWY 34R. WE THUS CANNOT PASS THIS ACFT. THEN WE WERE ISSUED A CLRNC TO MAINTAIN 170 KTS UNTIL 5 DME. THIS KEPT US ONLY ABOUT 200 YARDS BEHIND PRECEDING ACFT WITH A SLOW CLOSURE RATE. I WAS VERY PREOCCUPIED WITH OUR PROX. WE DON'T REMEMBER BEING SWITCHED TO TWR AND LANDED ON APCH FREQ. I DON'T FEEL THAT SPD RESTRS ARE APPROPRIATE WHEN CLRED TO 'MAINTAIN VISUAL SEPARATION.' WILL NOT ACCEPT THIS COMBO OF CLRNCS AGAIN IN FUTURE.