Narrative:

MD80 departed runway 34R approximately 1 min ahead of us and appeared to take up an initial heading of 320 degrees. We departed bluit three FMS departure. Departure control queried if we had visual on the MD80. Acknowledged 'yes' and told to maintain visual separation. As we both climbed towards 10000 ft, the MD80 was given a turn to the south (165 degrees or so). We were now heading 101 degrees on the FMS departure. The MD80 confirmed visual on us as well. We were cleared to 15000 ft and the MD80 to 11000 ft or 12000 ft. As the MD80 turned toward us, visually and TCASII in sight, I disconnected the autoplt and started a leveloff at approximately 10300 ft. Immediately thereafter, we got a TCASII warning to 'descend.' the MD80 flew over us approximately 700 ft and perhaps slightly behind us. In retrospect, did not expect that accepting 'visual separation' would mean that departure control would give us similar altitudes to climb to, or that conflicting headings would be encountered. Complicating factor was difficulty in really understanding position of the MD80 (well-lit with his lights all on) at night. TCASII gave best picture. The southerly turn given to the MD80 really got my attention. The first officer and I had good 'situational awareness,' started a descent prior to TCASII warning, but I won't be put in that situation again.

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Original NASA ASRS Text

Title: A B757 FLC EXPERIENCES A POTENTIAL CONFLICT WITH AN OPPOSITE DIRECTION MD80 PROGRAMMED TO CLB THROUGH THEIR ALT NE OF SEA, WA.

Narrative: MD80 DEPARTED RWY 34R APPROX 1 MIN AHEAD OF US AND APPEARED TO TAKE UP AN INITIAL HEADING OF 320 DEGS. WE DEPARTED BLUIT THREE FMS DEP. DEP CTL QUERIED IF WE HAD VISUAL ON THE MD80. ACKNOWLEDGED 'YES' AND TOLD TO MAINTAIN VISUAL SEPARATION. AS WE BOTH CLBED TOWARDS 10000 FT, THE MD80 WAS GIVEN A TURN TO THE S (165 DEGS OR SO). WE WERE NOW HEADING 101 DEGS ON THE FMS DEP. THE MD80 CONFIRMED VISUAL ON US AS WELL. WE WERE CLRED TO 15000 FT AND THE MD80 TO 11000 FT OR 12000 FT. AS THE MD80 TURNED TOWARD US, VISUALLY AND TCASII IN SIGHT, I DISCONNECTED THE AUTOPLT AND STARTED A LEVELOFF AT APPROX 10300 FT. IMMEDIATELY THEREAFTER, WE GOT A TCASII WARNING TO 'DSND.' THE MD80 FLEW OVER US APPROX 700 FT AND PERHAPS SLIGHTLY BEHIND US. IN RETROSPECT, DID NOT EXPECT THAT ACCEPTING 'VISUAL SEPARATION' WOULD MEAN THAT DEP CTL WOULD GIVE US SIMILAR ALTS TO CLB TO, OR THAT CONFLICTING HEADINGS WOULD BE ENCOUNTERED. COMPLICATING FACTOR WAS DIFFICULTY IN REALLY UNDERSTANDING POS OF THE MD80 (WELL-LIT WITH HIS LIGHTS ALL ON) AT NIGHT. TCASII GAVE BEST PICTURE. THE SOUTHERLY TURN GIVEN TO THE MD80 REALLY GOT MY ATTN. THE FO AND I HAD GOOD 'SITUATIONAL AWARENESS,' STARTED A DSCNT PRIOR TO TCASII WARNING, BUT I WON'T BE PUT IN THAT SIT AGAIN.

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.