Narrative:

During my shift I was working 6 combined sectors at ZSE. At approximately XX00, atx X, oak-pdx, checked on frequency south of fjs VORTAC and atx Y, pdx-oak, checked on at eug, both aircraft were operating VFR on top. The aircraft were on opposite courses and passed directly over each other. They were talking to each other on company frequency. When the aircraft passed each other the flight intentionally changed their beacon codes to the other aircraft's squawk. Maybe it was the hour of the day, but the data block swap was not noticed immediately. After some time had passed, I noticed that atx X was now headed sbound instead of northbound and atx Y was heading in the wrong direction. I asked the aircraft to identify. After that, I saw the codes change back to what they were originally assigned. A radio transmission was made that said something like, 'we wondered when you were going to catch that.' this irresponsible and unprofessional behavior should not be allowed in ATC system. Supplemental information from acn 235691: I worked shift in the D area at seattle ARTCC. I was signed on as the manual controller on sector 30. At approximately XX00 atx X checked on frequency VFR on top. The aircraft was rted from oak to pdx. At approximately the same time atx Y checked on frequency VFR on top. The aircraft was rted from pdx to oak. At approximately XX15 traffic was called to both aircraft. At approximately XX17 the aircraft passed northbound at 12500 ft and atx Y sbound at 11500 ft. The beacons were close enough to have no resolution. When resolution was reestablished the data block for atx X was proceeding sbound and the data block for atx Y was proceeding northbound. At approximately XX30 the aircraft were asked to identify. One of the aircraft transmitted 'we wondered how long it would take for you to notice that.' the aircraft then went back to their assigned beacon codes.

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Original NASA ASRS Text

Title: ATX X AND Y NON ADHERENCE TO ATC INSTRUCTION UNAUTH XPONDER CODE SWAP CAUSING DATA TAG SWAP. PLTDEV.

Narrative: DURING MY SHIFT I WAS WORKING 6 COMBINED SECTORS AT ZSE. AT APPROX XX00, ATX X, OAK-PDX, CHKED ON FREQ S OF FJS VORTAC AND ATX Y, PDX-OAK, CHKED ON AT EUG, BOTH ACFT WERE OPERATING VFR ON TOP. THE ACFT WERE ON OPPOSITE COURSES AND PASSED DIRECTLY OVER EACH OTHER. THEY WERE TALKING TO EACH OTHER ON COMPANY FREQ. WHEN THE ACFT PASSED EACH OTHER THE FLT INTENTIONALLY CHANGED THEIR BEACON CODES TO THE OTHER ACFT'S SQUAWK. MAYBE IT WAS THE HR OF THE DAY, BUT THE DATA BLOCK SWAP WAS NOT NOTICED IMMEDIATELY. AFTER SOME TIME HAD PASSED, I NOTICED THAT ATX X WAS NOW HEADED SBOUND INSTEAD OF NBOUND AND ATX Y WAS HDG IN THE WRONG DIRECTION. I ASKED THE ACFT TO IDENT. AFTER THAT, I SAW THE CODES CHANGE BACK TO WHAT THEY WERE ORIGINALLY ASSIGNED. A RADIO XMISSION WAS MADE THAT SAID SOMETHING LIKE, 'WE WONDERED WHEN YOU WERE GOING TO CATCH THAT.' THIS IRRESPONSIBLE AND UNPROFESSIONAL BEHAVIOR SHOULD NOT BE ALLOWED IN ATC SYS. SUPPLEMENTAL INFO FROM ACN 235691: I WORKED SHIFT IN THE D AREA AT SEATTLE ARTCC. I WAS SIGNED ON AS THE MANUAL CTLR ON SECTOR 30. AT APPROX XX00 ATX X CHKED ON FREQ VFR ON TOP. THE ACFT WAS RTED FROM OAK TO PDX. AT APPROX THE SAME TIME ATX Y CHKED ON FREQ VFR ON TOP. THE ACFT WAS RTED FROM PDX TO OAK. AT APPROX XX15 TFC WAS CALLED TO BOTH ACFT. AT APPROX XX17 THE ACFT PASSED NBOUND AT 12500 FT AND ATX Y SBOUND AT 11500 FT. THE BEACONS WERE CLOSE ENOUGH TO HAVE NO RESOLUTION. WHEN RESOLUTION WAS REESTABLISHED THE DATA BLOCK FOR ATX X WAS PROCEEDING SBOUND AND THE DATA BLOCK FOR ATX Y WAS PROCEEDING NBOUND. AT APPROX XX30 THE ACFT WERE ASKED TO IDENT. ONE OF THE ACFT XMITTED 'WE WONDERED HOW LONG IT WOULD TAKE FOR YOU TO NOTICE THAT.' THE ACFT THEN WENT BACK TO THEIR ASSIGNED BEACON CODES.

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.