Narrative:

We were initially cleared to cross runway 34R and hold short of runway 34L. In the process of crossing, we were cleared to take off on runway 34L. Upon turning onto the runway, the captain turned the aircraft over to me for takeoff. Apparently, after our clearance for takeoff, an F28 was cleared for takeoff from the parallel runway 34R. I do not know if the other aircraft was told to maintain visual separation, as I missed hearing their clearance. The first I knew of their departure was as they pulled into my peripheral view just prior to rotation. As seattle doesn't do simultaneous departures, I was surprised to see them next to us. Our clearance was the seattle 2 SID, which tracks basically straight out the sea 338 degree radial. I believe the F28 must have been light and was able to our-accelerate us so that we rotated at the same time. We were not slow in executing our takeoff clearance. At liftoff, neither the captain nor I knew if the other aircraft had been assigned a turn or was on the same SID we were on. We decided to offset our course to the left until the other aircraft's intentions were clear. Passing through 1100 ft, we receive the first of 4 RA's to descend, which we complied with. It was never necessary to actually descend, as just leveling off resulted in a 'clear of conflict' message. We had been switched to departure prior to the RA's with no communication to or from the tower regarding the other aircraft that I remember, though my captain thought the tower offhandedly mentioned the traffic beside us. Upon switching to departure, we asked for a left turn and advised them of the RA's we were receiving. He gave us a 15 degree left turn and mentioned our parallel traffic was a dash 8 (which it was not). After the turn, no further RA's resulted. I believe the tower meant for the F28 to follow us and maintain visual separation but gave the F28 takeoff clearance before we were actually rolling. The only other possibility that comes to mind is that they forgot we were there and since I can't remember the verbiage in their clearance, I don't know which is correct. I think ATC is under pressure to move so many airplanes, that giving a takeoff clearance with a 'maintain visual separation' caveat before the first aircraft has lifted off is accepted practice, despite possible hazards (such as wake turbulence). In this case, it would have been helpful to know if advance they would be performing closely spaced of simultaneous departures. We could have selected 'TA only' on the TCASII. And with closely spaced departures, I think departure aircraft should be given diverging headings as is done at sfo. If that were the case, no conflict (and therefore no RA's) would have resulted in this situation.

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Original NASA ASRS Text

Title: DEPS FROM CLOSELY SPACED RWYS RESULT IN TCASII RA WHEN ONE ACFT OVERTAKES ANOTHER AT SEA, WA.

Narrative: WE WERE INITIALLY CLRED TO CROSS RWY 34R AND HOLD SHORT OF RWY 34L. IN THE PROCESS OF XING, WE WERE CLRED TO TAKE OFF ON RWY 34L. UPON TURNING ONTO THE RWY, THE CAPT TURNED THE ACFT OVER TO ME FOR TKOF. APPARENTLY, AFTER OUR CLRNC FOR TKOF, AN F28 WAS CLRED FOR TKOF FROM THE PARALLEL RWY 34R. I DO NOT KNOW IF THE OTHER ACFT WAS TOLD TO MAINTAIN VISUAL SEPARATION, AS I MISSED HEARING THEIR CLRNC. THE FIRST I KNEW OF THEIR DEP WAS AS THEY PULLED INTO MY PERIPHERAL VIEW JUST PRIOR TO ROTATION. AS SEATTLE DOESN'T DO SIMULTANEOUS DEPS, I WAS SURPRISED TO SEE THEM NEXT TO US. OUR CLRNC WAS THE SEATTLE 2 SID, WHICH TRACKS BASICALLY STRAIGHT OUT THE SEA 338 DEG RADIAL. I BELIEVE THE F28 MUST HAVE BEEN LIGHT AND WAS ABLE TO OUR-ACCELERATE US SO THAT WE ROTATED AT THE SAME TIME. WE WERE NOT SLOW IN EXECUTING OUR TKOF CLRNC. AT LIFTOFF, NEITHER THE CAPT NOR I KNEW IF THE OTHER ACFT HAD BEEN ASSIGNED A TURN OR WAS ON THE SAME SID WE WERE ON. WE DECIDED TO OFFSET OUR COURSE TO THE L UNTIL THE OTHER ACFT'S INTENTIONS WERE CLR. PASSING THROUGH 1100 FT, WE RECEIVE THE FIRST OF 4 RA'S TO DSND, WHICH WE COMPLIED WITH. IT WAS NEVER NECESSARY TO ACTUALLY DSND, AS JUST LEVELING OFF RESULTED IN A 'CLR OF CONFLICT' MESSAGE. WE HAD BEEN SWITCHED TO DEP PRIOR TO THE RA'S WITH NO COM TO OR FROM THE TWR REGARDING THE OTHER ACFT THAT I REMEMBER, THOUGH MY CAPT THOUGHT THE TWR OFFHANDEDLY MENTIONED THE TFC BESIDE US. UPON SWITCHING TO DEP, WE ASKED FOR A L TURN AND ADVISED THEM OF THE RA'S WE WERE RECEIVING. HE GAVE US A 15 DEG L TURN AND MENTIONED OUR PARALLEL TFC WAS A DASH 8 (WHICH IT WAS NOT). AFTER THE TURN, NO FURTHER RA'S RESULTED. I BELIEVE THE TWR MEANT FOR THE F28 TO FOLLOW US AND MAINTAIN VISUAL SEPARATION BUT GAVE THE F28 TKOF CLRNC BEFORE WE WERE ACTUALLY ROLLING. THE ONLY OTHER POSSIBILITY THAT COMES TO MIND IS THAT THEY FORGOT WE WERE THERE AND SINCE I CAN'T REMEMBER THE VERBIAGE IN THEIR CLRNC, I DON'T KNOW WHICH IS CORRECT. I THINK ATC IS UNDER PRESSURE TO MOVE SO MANY AIRPLANES, THAT GIVING A TKOF CLRNC WITH A 'MAINTAIN VISUAL SEPARATION' CAVEAT BEFORE THE FIRST ACFT HAS LIFTED OFF IS ACCEPTED PRACTICE, DESPITE POSSIBLE HAZARDS (SUCH AS WAKE TURB). IN THIS CASE, IT WOULD HAVE BEEN HELPFUL TO KNOW IF ADVANCE THEY WOULD BE PERFORMING CLOSELY SPACED OF SIMULTANEOUS DEPS. WE COULD HAVE SELECTED 'TA ONLY' ON THE TCASII. AND WITH CLOSELY SPACED DEPS, I THINK DEP ACFT SHOULD BE GIVEN DIVERGING HDGS AS IS DONE AT SFO. IF THAT WERE THE CASE, NO CONFLICT (AND THEREFORE NO RA'S) WOULD HAVE RESULTED IN THIS SIT.

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.