Narrative:

Checked on with departure and departure assigned us 4000 ft. Almost immediately TCASII 'traffic' alert sounded and simultaneously departure control called VFR traffic to us. Traffic was showing +400 on display. We were in a climbing right turn (approximately heading 050 degrees) and climbing through 2000 ft. I began searching for traffic. TCASII 'monitor vertical speed' sounded and captain complied (RA was to climb at approximately 2000 FPM). I spotted aircraft at my 12:30 O'clock position and it appeared to be moving from our right to left. TCASII now sounded 'climb, climb.' at this point, I believe the captain saw the airplane as our right bank angle increased. The aircraft (a cessna) passed slightly low off our left. Once past, the captain leveled and rolled out of the bank. Ironically, we rolled out on our assigned heading of 090 degrees and altitude was approximately 3500 ft. Captain queried ATC. Departure said they were not working the cessna but mdw tower was. He asked if tower had told us about the traffic, we responded no. In retrospect, I saw the aircraft initially, the captain did not -- since the captain was flying. I believe there was no choice but to comply with the RA. Due to the captain's actions, I did not believe we were in danger of hitting the airplane. Had we hesitated or not complied then the outcome might not have been as successful. Supplemental information from acn 541483: we began to level off in order to stay below the traffic. It moved to our 12 O'clock position and was showing at our altitude. We still did not have visual due to haze and an uneven overcast ceiling. We then got TCASII 'monitor vertical speed,' vsi indications and 'climb, climb.' I steepened the bank to the right and initiated a 1800-2000 FPM climb as indicated on the vsi. Simultaneously, we saw the traffic, a white single engine cessna with brown or black stripes at our 12 O'clock position and at our altitude 2000 ft in front of us. The traffic appeared to be in a turn, possibly descending. In the evasive maneuver we heard a momentary stick shaker and 'bank angle' warning. I believe this action was necessary to avoid the traffic. The cessna passed off our left wing slightly below us and appeared to be 1000-1500 ft laterally from our aircraft. After passing, we continued our 090 degree heading and climbed to 4000 ft. We never deviated from any ATC clearance. The flight attendants confirmed that everyone was seated in the cabin and there were no injuries reported. I made a PA after leaving 10000 ft to explain to the passenger what happened. This entire event took place in approximately 15-20 seconds, therefore, several of the reported events were happening simultaneously.

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Original NASA ASRS Text

Title: A B737-300 CREW RECEIVE TCASII ALERT JUST AFTER DEPARTING MDW WHICH RESULTED IN AN NMAC.

Narrative: CHKED ON WITH DEP AND DEP ASSIGNED US 4000 FT. ALMOST IMMEDIATELY TCASII 'TFC' ALERT SOUNDED AND SIMULTANEOUSLY DEP CTL CALLED VFR TFC TO US. TFC WAS SHOWING +400 ON DISPLAY. WE WERE IN A CLBING R TURN (APPROX HDG 050 DEGS) AND CLBING THROUGH 2000 FT. I BEGAN SEARCHING FOR TFC. TCASII 'MONITOR VERT SPD' SOUNDED AND CAPT COMPLIED (RA WAS TO CLB AT APPROX 2000 FPM). I SPOTTED ACFT AT MY 12:30 O'CLOCK POS AND IT APPEARED TO BE MOVING FROM OUR R TO L. TCASII NOW SOUNDED 'CLB, CLB.' AT THIS POINT, I BELIEVE THE CAPT SAW THE AIRPLANE AS OUR R BANK ANGLE INCREASED. THE ACFT (A CESSNA) PASSED SLIGHTLY LOW OFF OUR L. ONCE PAST, THE CAPT LEVELED AND ROLLED OUT OF THE BANK. IRONICALLY, WE ROLLED OUT ON OUR ASSIGNED HDG OF 090 DEGS AND ALT WAS APPROX 3500 FT. CAPT QUERIED ATC. DEP SAID THEY WERE NOT WORKING THE CESSNA BUT MDW TWR WAS. HE ASKED IF TWR HAD TOLD US ABOUT THE TFC, WE RESPONDED NO. IN RETROSPECT, I SAW THE ACFT INITIALLY, THE CAPT DID NOT -- SINCE THE CAPT WAS FLYING. I BELIEVE THERE WAS NO CHOICE BUT TO COMPLY WITH THE RA. DUE TO THE CAPT'S ACTIONS, I DID NOT BELIEVE WE WERE IN DANGER OF HITTING THE AIRPLANE. HAD WE HESITATED OR NOT COMPLIED THEN THE OUTCOME MIGHT NOT HAVE BEEN AS SUCCESSFUL. SUPPLEMENTAL INFO FROM ACN 541483: WE BEGAN TO LEVEL OFF IN ORDER TO STAY BELOW THE TFC. IT MOVED TO OUR 12 O'CLOCK POS AND WAS SHOWING AT OUR ALT. WE STILL DID NOT HAVE VISUAL DUE TO HAZE AND AN UNEVEN OVCST CEILING. WE THEN GOT TCASII 'MONITOR VERT SPD,' VSI INDICATIONS AND 'CLB, CLB.' I STEEPENED THE BANK TO THE R AND INITIATED A 1800-2000 FPM CLB AS INDICATED ON THE VSI. SIMULTANEOUSLY, WE SAW THE TFC, A WHITE SINGLE ENG CESSNA WITH BROWN OR BLACK STRIPES AT OUR 12 O'CLOCK POS AND AT OUR ALT 2000 FT IN FRONT OF US. THE TFC APPEARED TO BE IN A TURN, POSSIBLY DSNDING. IN THE EVASIVE MANEUVER WE HEARD A MOMENTARY STICK SHAKER AND 'BANK ANGLE' WARNING. I BELIEVE THIS ACTION WAS NECESSARY TO AVOID THE TFC. THE CESSNA PASSED OFF OUR L WING SLIGHTLY BELOW US AND APPEARED TO BE 1000-1500 FT LATERALLY FROM OUR ACFT. AFTER PASSING, WE CONTINUED OUR 090 DEG HDG AND CLBED TO 4000 FT. WE NEVER DEVIATED FROM ANY ATC CLRNC. THE FLT ATTENDANTS CONFIRMED THAT EVERYONE WAS SEATED IN THE CABIN AND THERE WERE NO INJURIES RPTED. I MADE A PA AFTER LEAVING 10000 FT TO EXPLAIN TO THE PAX WHAT HAPPENED. THIS ENTIRE EVENT TOOK PLACE IN APPROX 15-20 SECONDS, THEREFORE, SEVERAL OF THE RPTED EVENTS WERE HAPPENING SIMULTANEOUSLY.

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.