Narrative:

We were following a metropolitan on the taxi out to the active runways (runway 16L&right) with no other aircraft behind us on the taxiway. Approaching the end of the runways, we heard and observed a B737 checking on with tower for runway 16L. Both the first officer and myself made the comment that they were very high and wondered if they would make the runway. I also observed a DHC8 on a several mi final for runway 16R. Tower cleared the metropolitan to 'position and hold' on runway 16L, then several seconds later told the metropolitan to 'move up to allow a DHC8 to pass behind you.' we were then given a clearance which I thought, and still think, was to 'cross runway 16L and position and hold runway 16R.' after my first officer read back the clearance, I repeated, 'cross runway 16L and position and hold runway 16R.' I then told the first officer to go below the line on the checklist as I turned on the taxi and white anti-collision lights. He complied. I also said 'clear left' (landing traffic was approaching from the right) and looked to the right and saw the first officer look to the right as well and nod in agreement. Our company procedures are to go below the line only when cleared for takeoff or position and hold on active runways. As we passed the hold short line of runway 16R, the DHC8 on final asked tower 'verified to land runway 16R.' at this point we were making the turn onto the runway and I got a better look at the DHC8 and realized they were a lot closer than I thought. Then tower quickly told us 'cleared immediate takeoff runway 16R.' the DHC8 on final made the landing with adequate clearance and we were given a turn to a heading of 230 degrees and were politely thanked for our help as we were passed to departure control. As soon as we reached our destination, I called seatac tower and asked to speak to the supervisor. I asked for his interpretation of what happened. He said that the B737 went around, but it was because they were too high and had nothing to do with us on the west runway. He told me he felt the situation worked out well and had no problem with what happened. A possible misunderstanding of a clearance was what led to this situation. After thinking about it for a while, I began to realize how 'position and hold' and 'hold short' could be confused in a rushed situation or rushed communication. Both clrncs have the word 'hold' in them. I fly in canada a lot and they have a different clearance for 'position and hold.' instead we are given the clearance 'position only on runway 27R.' I now realize the advantage to this as nowhere in the clearance is there the word 'hold.' their 'hold short' clearance is the same as ours. With this system, only 1 clearance has the word 'hold' in it.

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Original NASA ASRS Text

Title: DHC8 PLT ENTERS RWY AT SEA BELIEVING HE OR SHE HAD ATC CLRNC.

Narrative: WE WERE FOLLOWING A METRO ON THE TAXI OUT TO THE ACTIVE RWYS (RWY 16L&R) WITH NO OTHER ACFT BEHIND US ON THE TXWY. APPROACHING THE END OF THE RWYS, WE HEARD AND OBSERVED A B737 CHKING ON WITH TWR FOR RWY 16L. BOTH THE FO AND MYSELF MADE THE COMMENT THAT THEY WERE VERY HIGH AND WONDERED IF THEY WOULD MAKE THE RWY. I ALSO OBSERVED A DHC8 ON A SEVERAL MI FINAL FOR RWY 16R. TWR CLRED THE METRO TO 'POS AND HOLD' ON RWY 16L, THEN SEVERAL SECONDS LATER TOLD THE METRO TO 'MOVE UP TO ALLOW A DHC8 TO PASS BEHIND YOU.' WE WERE THEN GIVEN A CLRNC WHICH I THOUGHT, AND STILL THINK, WAS TO 'CROSS RWY 16L AND POS AND HOLD RWY 16R.' AFTER MY FO READ BACK THE CLRNC, I REPEATED, 'CROSS RWY 16L AND POS AND HOLD RWY 16R.' I THEN TOLD THE FO TO GO BELOW THE LINE ON THE CHKLIST AS I TURNED ON THE TAXI AND WHITE ANTI-COLLISION LIGHTS. HE COMPLIED. I ALSO SAID 'CLR L' (LNDG TFC WAS APCHING FROM THE R) AND LOOKED TO THE R AND SAW THE FO LOOK TO THE R AS WELL AND NOD IN AGREEMENT. OUR COMPANY PROCS ARE TO GO BELOW THE LINE ONLY WHEN CLRED FOR TKOF OR POS AND HOLD ON ACTIVE RWYS. AS WE PASSED THE HOLD SHORT LINE OF RWY 16R, THE DHC8 ON FINAL ASKED TWR 'VERIFIED TO LAND RWY 16R.' AT THIS POINT WE WERE MAKING THE TURN ONTO THE RWY AND I GOT A BETTER LOOK AT THE DHC8 AND REALIZED THEY WERE A LOT CLOSER THAN I THOUGHT. THEN TWR QUICKLY TOLD US 'CLRED IMMEDIATE TKOF RWY 16R.' THE DHC8 ON FINAL MADE THE LNDG WITH ADEQUATE CLRNC AND WE WERE GIVEN A TURN TO A HDG OF 230 DEGS AND WERE POLITELY THANKED FOR OUR HELP AS WE WERE PASSED TO DEP CTL. AS SOON AS WE REACHED OUR DEST, I CALLED SEATAC TWR AND ASKED TO SPEAK TO THE SUPVR. I ASKED FOR HIS INTERP OF WHAT HAPPENED. HE SAID THAT THE B737 WENT AROUND, BUT IT WAS BECAUSE THEY WERE TOO HIGH AND HAD NOTHING TO DO WITH US ON THE W RWY. HE TOLD ME HE FELT THE SIT WORKED OUT WELL AND HAD NO PROB WITH WHAT HAPPENED. A POSSIBLE MISUNDERSTANDING OF A CLRNC WAS WHAT LED TO THIS SIT. AFTER THINKING ABOUT IT FOR A WHILE, I BEGAN TO REALIZE HOW 'POS AND HOLD' AND 'HOLD SHORT' COULD BE CONFUSED IN A RUSHED SIT OR RUSHED COM. BOTH CLRNCS HAVE THE WORD 'HOLD' IN THEM. I FLY IN CANADA A LOT AND THEY HAVE A DIFFERENT CLRNC FOR 'POS AND HOLD.' INSTEAD WE ARE GIVEN THE CLRNC 'POS ONLY ON RWY 27R.' I NOW REALIZE THE ADVANTAGE TO THIS AS NOWHERE IN THE CLRNC IS THERE THE WORD 'HOLD.' THEIR 'HOLD SHORT' CLRNC IS THE SAME AS OURS. WITH THIS SYS, ONLY 1 CLRNC HAS THE WORD 'HOLD' IN IT.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.