MD-83
Conflict Airborne Conflict
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance; Flight Crew Took Evasive Action
Airspace Structure; Procedure
We were on a vector and a climb to 13;000. ATC called traffic ahead and I could see on the TCAS that if I continued to climb to 13;000 there could be a conflict. About 12;500; I decreased our climb rate trying to avoid a conflict with traffic that we could not see visually. I did finally see the aircraft which passed off our right side about the same altitude. This was somewhere between 12;500 and 13;000 FT. I don't know the lateral separation. We received a TCAS RA telling us to descend which I followed. It was a rather aggressive RA calling for about 1;800 FT per minute descent. During this maneuver; we noticed another target on our left. I'm not sure if the RA was for the first or second airplane. The planes appeared to be in a loose formation. I think they were military but not sure. The first plane that I saw was small. Neither the Captain nor myself saw the 2nd one because my attention was directed inside the plane at the VSI directing the RA. I don't know how close the 2nd plane was. We advised ATC we were responding to a RA. ATC seemed surprised. After the RA was complete; I started the climb once again to 13;000. We then switched frequencies and continued the flight.
The First Officer was the pilot flying and after we switched over to Departure we were given an intermediate altitude of 7;000 FT. Eventually we were given a climb to 17;000 and switched over to Center. Climbing north; Center gave us another intermediate altitude of 13;000 while climbing through 11;800 because of conflicting traffic. The TCAS system had the conflicting aircraft crossing our path from left to right heading in a southeast direction. I put 13;000 in the altitude window while the First Officer slowly approached 13;000. I noticed the incoming aircraft was lower than 13;500 and we received a Traffic Advisory. A second aircraft about a mile or two behind the first target gave us a Resolution Advisory (RA) and the First Officer descended abruptly because we were commanded a 1;500 FT descend to avoid the approaching aircraft. I announced to Center we were descending due to the RA and once clear we climbed back up to 13;000 without any more conflicts. We only had a visual on the leading aircraft and the rest of the flight was uneventful.
MD83 flight crew reports responding to a TCAS RA during climb to 13;000 FT caused by military aircraft; in loose formation; below 13;500 FT.