DURING A NIGHT OP; AN ATC SPONSORED RWY INCURSION OF RWY 16L BY A B737 CREW CREATES THE NECESSITY FOR LCL CTLR TO SEND AN ACR ON SHORT FINAL AROUND AT SEA; WA.

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AFTER LNDG ON RWY 16R; WE WERE HOLDING BTWN THE RWYS WAITING FOR ACR FLT Y TO LAND AND ROLL OUT ON RWY 16L. I HAD OVERHEARD ON 131.2 ON FINAL APCH THAT THERE WAS A GATE PROB WITH SEVERAL ACFT. SO WHEN I KNEW WE WERE WAITING FOR ACFT Y TO LAND; I CALLED OPS TO VERIFY THAT OUR GATE WAS OPEN. WHILE I WAS TALKING TO OPS; PIC PUSHED THE PWR UP TO CROSS RWY 16L. BEFORE I HAD A CHANCE TO SAY ANYTHING; HE STOPPED THE ACFT WHEN TWR ADVISED HIM TO. AS IT TURNED OUT; TWR TOLD US TO CROSS RWY 16L; BUT THEN REALIZED THAT ACR Y WAS TOO CLOSE TO TOUCHING DOWN. AND SINCE WE WERE ALREADY ACROSS THE HOLD SHORT LINE; THEY SENT ACR Y AROUND. WHEN WE GOT TO THE GATE; PIC CALLED THE TWR TO VERIFY WHAT HAD HAPPENED. THEY TOLD HIM THAT IT WAS THEIR MISTAKE AND THEY DID THE PRUDENT THING IN SENDING ACR Y AROUND. SUPPLEMENTAL INFO FROM ACN 603192: AS WE MOVED ACROSS THE HOLD SHORT LINE; TWR INSTRUCTED US TO HOLD OUR POS. IT APPEARED TO ME WE COULD HAVE CROSSED THE RWY IN TIME BUT FACTORS FROM MY SEAT WERE: 1) NIGHT TIME VISIBILITY; AND 2) DIFFICULT ANGLE LOOKING BACK UP RWY 16L FROM THE ANGLED TXWY.