ON ILS RWY 10L APCH TO PDX; B767 FLC RECEIVES TCAS RA DUE TO PATTERN TFC AT VUO ARPT. PDX ADVISED COMMON OCCURRENCE.

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ON ILS TO RWY 10L AT PDX; TRACON CALLED OUT TFC 11 O'CLOCK. 'NO CONTACT;' WAS OUR REPLY. WE OBSERVED THE TFC ON TCAS; CLOSING ON US AND 500 FT BELOW US; WITH VERTICAL SEPARATION DECREASING. WHEN TCAS SHOWED US WITHIN 300 FT; WE RECEIVED RA 'MONITOR VERTICAL SPEED.' IT APPEARED ON TCAS THAT WE PASSED DIRECTLY OVER THE TFC WITH APPROX 300 FT SEPARATION. TWR SAID TFC WAS A VFR ACFT EXECUTING TOUCH AND GOES AT PEARSON ARPT; AND THAT THIS TCAS EVENT HAPPENS ALL THE TIME. I SUBMIT TO YOU THAT 1) ATC IS NOT PROVIDING ADEQUATE SEPARATION FROM OTHER TFC. 2) IF THIS OPERATION IS PERMITTED TO CONTINUE; EVENTUALLY 2 ACFT ARE GOING TO COLLIDE TO THE W OF KPDX; NEAR PEARSON ARPT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR WAS ABOUT TO EXECUTE A TCAS EVASIVE ACTION WHEN THE ALERT DOWNGRADED TO A 'TA.' RPTR SUGGEST ARPT BE CLOSED; OR ATC RESTR PATTERN OPS. SUPPLEMENTAL INFO: VUO ARPT REPRESENTATIVE ADVISED THAT THEY HAVE BEEN AWARE OF SOME ACR CONCERNS SINCE THE ILS RWY 10L APCH WAS IMPLEMENTED IN 1996. IT IS ALLEGED THAT THE GS NOT BE ESTABLISHED AT ITS PRESENT 3.0 ANGLE; BUT BE DESIGNED AT A STEEPER GRADIENT. IT WAS NOT. THE REPRESENTATIVE STATED THAT VUO WAS AN OPERATING ARPT LONG BEFORE THERE EVER WAS A PDX ARPT. THE REPRESENTATIVE ADVISED THAT HE WAS NOT AWARE OF ANY RPTED TCAS EVENTS WHEN THE ILS RWY 10R APCH WAS THE ONLY PUBLISHED INSTRUMENT APCH PROC TO RWYS 10. A TWR SPECIALIST ADVISED THAT GENERAL TFC ADVISORIES ARE ISSUED TO ACFT ON APCH TO RWY'S 10 BY TRACON AND TWR; WHEN OBSERVED. ATC RECEIVES FREQ REMARKS FROM ACFT ADVISING OF A TCAS ALERT WHEN PASSING IN THE VICINITY OF VUO ARPT; WHICH IS INSIDE THE RWY 10L FINAL APCH FIX; AND DESCENDING THROUGH APPROX 1300 FT. VUO TFC IS REQUIRED TO CALL PDX TWR PRIOR TO ENTERING AND DEPING VUO ARPT. THERE ARE ACFT FREQUENTLY OPERATION WITHIN THE VUO TFC PATTERN ON UNICOM FREQ. VUO HAS A SPECIFIC ARPT FREQ THAT IS CONTINUOUSLY MONITORED AT PDX TWR. IT HAS BEEN SUGGESTED THAT CHANGING THE ILS RWY 10L GLIDE PATH MIGHT DIMINISH THE NUMBER OF TCAS ALERTS FOR ACFT PASSING IN THE VICINITY OF VUO ARPT.