Narrative:

On approach we were cleared to land on runway 13R while 8 mi out on the visual approach. Bfi uses runway 13R for turbojet aircraft (10000 ft length) and runway 13L for light aircraft (5000 ft length). As we were on a 1 mi final we noticed a light aircraft on a left base for what we assumed to be the left runway. As the 2 runways utilize different tower frequencys we were unable to monitor his intentions. As he began his turn to final, he overshot the turn slightly and strayed onto our final approach course. I moved slightly to the right of centerline to give him more room. At this point, we were both about 200 ft AGL and he continued to move toward us. I could move no further to the right so I executed a missed approach. In a subsequent phone conversation with the tower controller we learned that the light aircraft had been cleared to land on runway 13L but landed on our runway, the wrong runway, runway 13R. He (other pilot) said he never saw us. The tower controller told us that he (other pilot) had 'no clue' about airport traffic flow, taxi instructions, etc. While en route to this airport he had violated another airport's class D airspace, that tower was looking to have a conversation with him as well. No enforcement action was taken.

Related reports:

Google
 

Original NASA ASRS Text

Title: ACFT LNDG ON WRONG RWY CAUSES ANOTHER TO GO AROUND.

Narrative: ON APCH WE WERE CLRED TO LAND ON RWY 13R WHILE 8 MI OUT ON THE VISUAL APCH. BFI USES RWY 13R FOR TURBOJET ACFT (10000 FT LENGTH) AND RWY 13L FOR LIGHT ACFT (5000 FT LENGTH). AS WE WERE ON A 1 MI FINAL WE NOTICED A LIGHT ACFT ON A L BASE FOR WHAT WE ASSUMED TO BE THE L RWY. AS THE 2 RWYS UTILIZE DIFFERENT TWR FREQS WE WERE UNABLE TO MONITOR HIS INTENTIONS. AS HE BEGAN HIS TURN TO FINAL, HE OVERSHOT THE TURN SLIGHTLY AND STRAYED ONTO OUR FINAL APCH COURSE. I MOVED SLIGHTLY TO THE R OF CTRLINE TO GIVE HIM MORE ROOM. AT THIS POINT, WE WERE BOTH ABOUT 200 FT AGL AND HE CONTINUED TO MOVE TOWARD US. I COULD MOVE NO FURTHER TO THE R SO I EXECUTED A MISSED APCH. IN A SUBSEQUENT PHONE CONVERSATION WITH THE TWR CTLR WE LEARNED THAT THE LIGHT ACFT HAD BEEN CLRED TO LAND ON RWY 13L BUT LANDED ON OUR RWY, THE WRONG RWY, RWY 13R. HE (OTHER PLT) SAID HE NEVER SAW US. THE TWR CTLR TOLD US THAT HE (OTHER PLT) HAD 'NO CLUE' ABOUT ARPT TFC FLOW, TAXI INSTRUCTIONS, ETC. WHILE ENRTE TO THIS ARPT HE HAD VIOLATED ANOTHER ARPT'S CLASS D AIRSPACE, THAT TWR WAS LOOKING TO HAVE A CONVERSATION WITH HIM AS WELL. NO ENFORCEMENT ACTION WAS TAKEN.

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.