TWR UNABLE TO COM WITH SMA ON RWY AWAITING TKOF CLRNC WITH LGT JET ON FINAL. JET WENT AROUND SMA AND TWR COMMUNICATED; SMA TAXIED OFF RWY AND WAS RECLRED FOR TKOF.

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WE WERE CLRED 'INTO POS AND HOLD; PREPARE FOR AN IMMEDIATE TKOF; XX JET ON A 7 MI FINAL'. WE ACKNOWLEDGED WE WERE READY FOR AN IMMEDIATE DEP AS WE TAXIED INTO POS. THE ACFT LNDG DID NOT EXIT UNTIL WELL DOWN THE 8000 FT RWY. AS WE SAT THERE WAITING WE HEARD THE XX JET INBOUND CALL A 6 MI FINAL. TWR 'ROGERED'; 'CLRED TO LAND'. ABOUT THIS TIME THE SMA ACFT CLRED THE RWY. WE EXPECTED AN IMMEDIATE RELEASE AND AFTER A SHORT PAUSE (IT SOUNDED LIKE A BRIEF CARRIER WAVE BUT NO VOICE ON THE TWR FREQ) I CALLED THE TWR AND ASKED IF WE WERE CLRED FOR TKOF. NO RESPONSE FROM THE TWR. THE XX CALLED A 5 MI FINAL. I CALLED THE TWR AGAIN; 'ARE WE CLRED FOR TKOF'? NO RESPONSE. THE XX CALLED A 3 OR 4 MI FINAL. I CALLED THE TWR AGAIN AND STILL GOT NO RESPONSE. THEN THE XX ACFT CALLED A 2 MI FINAL. AT THIS TIME AN SMT JET HOLDING SHORT OF THE RWY XMITTED ON THE TWR FREQ 'XX JET THERE IS AN SMA ON THE END OF THE RWY'. THE XX THEN XMITTED 'GOING AROUND'. A FEW MOMENTS LATER WE SAW THE AIRLINER PASS OVER OUR ACFT IN THE PROCESS OF A GAR. AFTER THE AIRLINER PASSED BY THE TWR; THE TWR XMITTED FOR US TO 'EXPEDITE OFF THE RWY; YOUR RADIO IS NOT SUITABLE FOR FLT'. WE EXITED THE RWY VIA THE FIRST TAXIWAY AND CONTACTED GND. I CONTACTED PDX GND AND REQUESTED TO 'TAXI BACK FOR DEP'. GND RESPONDED 'TAXI TO 28R'. INCREDIBLE. WE ALMOST HAD AN XX JET LAND ON TOP OF US. I DON'T KNOW WHAT HAPPENED IN THE TWR -- A CTLR CHANGE IN PROGRESS OR WHAT. LOOKING BACK ON THE INCIDENT; I PROBABLY SHOULD HAVE TAXIED BACK OFF THE RWY AFTER THE TWR DIDN'T ANSWER MY SECOND CALL. ALTHOUGH I BELIEVE THE XX JET KNEW WE WERE STILL ON THE RWY; THE SMT JET XMISSION MAY HAVE SAVED OUR LIVES. I DON'T BELIEVE I WILL EVER TAXI INTO POS AND HOLD ON A RWY AGAIN UNLESS I CAN SEE THE FINAL APCH PATH WHILE AWAITING CLRNC FOR TKOF.