Narrative:

We took off runway 34L sea and cleared sea 2 departure to victoria (yyj) flight plan route, maintain 9000 250 KTS or less until further advised. Tower advised us to maintain visual separation on a departing aircraft. Approximately 8-10 NM north of sea, we got a vector to about 300 degree heading, then 250 degree heading, then 240 degree heading to intercept the airway (J-502, sea 307 degree radial). Also, we got climb clearance to 15000. Climbing through about 11000, departure controller told us to descend immediately to 10000 and turn back to a 250 degree heading to avoid air carrier Y at 1-2 O'clock and 5 mi at 11000. I disconnected the autoplt and automatic throttles (LNAV and VNAV had engaged to capture the airway and climb) to expedite the turn and descent, also TCASII was giving us a 'climb' solution to avoid air carrier Y but the first officer had the traffic in sight and we complied with departure controller instructions. Traffic passed off the right at 4-5 mi. We had climbed up to about 11000 before descending back to 10000. After giving us the turn and descent sea departure stated that our clearance was to intercept the sea 278 degree radial. After we changed to sea center, we asked what our clearance was after the sea 278 degree radial. Sea cleared us present position direct anc. Some of the flight attendants and passenger were alarmed by the turn, descent, and power reduction to avoid the traffic. There was obviously a difference between what we thought our clearance was: i.e., J-502, 307 degree radial to yyj and departure control sea 278 degree radial. I feel that sea departure should have used heading and altitude separation, rather than radial separation to clear traffic. I.e., different in mi between sea 278 degree and 307 degree at 10-15 NM is not very great. First and only traffic call was to turn and descend immediately.

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Original NASA ASRS Text

Title: ACR X POSSIBLE LTSS FROM ACR Y. POSSIBLE SYS ERROR.

Narrative: WE TOOK OFF RWY 34L SEA AND CLRED SEA 2 DEP TO VICTORIA (YYJ) FLT PLAN RTE, MAINTAIN 9000 250 KTS OR LESS UNTIL FURTHER ADVISED. TWR ADVISED US TO MAINTAIN VISUAL SEPARATION ON A DEPARTING ACFT. APPROX 8-10 NM N OF SEA, WE GOT A VECTOR TO ABOUT 300 DEG HDG, THEN 250 DEG HDG, THEN 240 DEG HDG TO INTERCEPT THE AIRWAY (J-502, SEA 307 DEG RADIAL). ALSO, WE GOT CLB CLRNC TO 15000. CLBING THROUGH ABOUT 11000, DEP CTLR TOLD US TO DSND IMMEDIATELY TO 10000 AND TURN BACK TO A 250 DEG HDG TO AVOID ACR Y AT 1-2 O'CLOCK AND 5 MI AT 11000. I DISCONNECTED THE AUTOPLT AND AUTO THROTTLES (LNAV AND VNAV HAD ENGAGED TO CAPTURE THE AIRWAY AND CLB) TO EXPEDITE THE TURN AND DSCNT, ALSO TCASII WAS GIVING US A 'CLB' SOLUTION TO AVOID ACR Y BUT THE FO HAD THE TFC IN SIGHT AND WE COMPLIED WITH DEP CTLR INSTRUCTIONS. TFC PASSED OFF THE R AT 4-5 MI. WE HAD CLBED UP TO ABOUT 11000 BEFORE DSNDING BACK TO 10000. AFTER GIVING US THE TURN AND DSCNT SEA DEP STATED THAT OUR CLRNC WAS TO INTERCEPT THE SEA 278 DEG RADIAL. AFTER WE CHANGED TO SEA CENTER, WE ASKED WHAT OUR CLRNC WAS AFTER THE SEA 278 DEG RADIAL. SEA CLRED US PRESENT POS DIRECT ANC. SOME OF THE FLT ATTENDANTS AND PAX WERE ALARMED BY THE TURN, DSCNT, AND PWR REDUCTION TO AVOID THE TFC. THERE WAS OBVIOUSLY A DIFFERENCE BTWN WHAT WE THOUGHT OUR CLRNC WAS: I.E., J-502, 307 DEG RADIAL TO YYJ AND DEP CTL SEA 278 DEG RADIAL. I FEEL THAT SEA DEP SHOULD HAVE USED HDG AND ALT SEPARATION, RATHER THAN RADIAL SEPARATION TO CLR TFC. I.E., DIFFERENT IN MI BTWN SEA 278 DEG AND 307 DEG AT 10-15 NM IS NOT VERY GREAT. FIRST AND ONLY TFC CALL WAS TO TURN AND DSND IMMEDIATELY.

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.