A B737-700 FLC EXPERIENCES A TEMPORARY LOSS OF COM FREQ WITH APCH CTLR WHEN INADVERTENTLY SWITCHING TO LCL CTLR 12 MI E OF PDX; OR.

Narrative

ON VECTOR HDG BASE LEG TO ILS RWY 28R; IN IMC AND COMMUNICATING WITH APCH CTLR ON FREQ 124.35. I (CAPT AND CHK AIRMAN) ATTEMPTED TO PRESELECT THE TWR FREQ 123.77 INTO THE UNUSED SIDE OF THE COM #1 PANEL AND INADVERTENTLY TUNED-OVER THE ACTIVE APCH FREQ. I REALIZED MY ERROR AFTER ABOUT 1 MIN AND RETURNED TO APCH FREQ IMMEDIATELY; CHKING IN AS WE CROSSED THROUGH THE LOC. THE CTLR GAVE US A HDG 'R TURN 310 DEGS TO INTERCEPT THE RWY 28R LOC AND CLRED FOR THE APCH.' NO CONFLICTS WITH OTHER TFC WERE NOTED AND APCH CTLR HANDED US OFF TO TWR. I MISSED MY INTERCEPT HDG AND CLRNC BECAUSE OF THIS MISTAKE. CONTRIBUTING FACTORS: DAY 5 OF DUTY. XA00 WAKE-UP AFTER 6 HRS SLEEP. TRAINING THE PF (FO) ON THE FIRST LEG OF HIS FIRST OPERATING EXPERIENCE TRIP AS A FO. ON THIS TYPE ACFT AT THIS AIRLINE; HIGH WORKLOAD. WE PLANNED ILS RWY 28R BEFORE TOP OF DSCNT; APCH CHANGED IT TO ILS RWY 28L AT 11000 FT; SO WE REPROGRAMMED THE FMC; AND APCH CTL THEN CHANGED OUR APCH BACK TO ILS RWY 28R WHEN WE WERE AT 3000 FT ON BASE LEG -- HIGH WORKLOAD AGAIN. I TRIED TO REDUCE WORKLOAD BY PRESELECTING TWR FREQ BUT I ENDED UP COMPROMISING SAFETY AND DOUBLING MY WORKLOAD. NEVER AGAIN!