Air carrier on arrival has 2 TA's then RA to climb.

Attributes
ACN	192608
Time
Date	199110
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : dfw
State Reference	TX
Altitude	msl bound lower : 3000 msl bound upper : 3400
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dfw
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent : approach descent other
Route In Use	approach : visual arrival other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 70 flight time total : 2300 flight time type : 1010
ASRS Report	192608
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 15000 flight time type : 3000
ASRS Report	192153
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : nmac non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Miss Distance	vertical : 400
Supplementary
Primary Problem	Ambiguous

Narrative:

On arrival to dfw we were approximately 10 DME north at 3000 ft. We were cleared for visual approach to runway 17L. We got 2 TA's from TCASII and did not see the traffic. Then we got an RA to climb. Climbed to 3400 ft and were then instructed 'check vertical speed' on TCASII. We never did see the traffic and ATC did not call out traffic to us or query our climb to 3400 ft. On our TCASII vertical speed indicator display we saw traffic at 400 ft below us. Upon landing at dfw the captain called ATC about situation. ATC said he did not see conflict but would follow up on it also. Company TCASII pilot/observer event questionnaire submitted. My guess is that a VFR traffic not in control with required approach was legal under the floor of TCA (3000 MSL). Maybe at 2800 ft MSL and the TCASII had us climb to 3400 ft to get 500 ft vertical separation. I feel this will become a common occurrence. I own an small aircraft and find it hard to get cleared in TCA so VFR under is common for GA to get around dfw.

Original NASA ASRS Text

Title: ACR ON ARR HAS 2 TA'S THEN RA TO CLB.

Narrative: ON ARR TO DFW WE WERE APPROX 10 DME N AT 3000 FT. WE WERE CLRED FOR VISUAL APCH TO RWY 17L. WE GOT 2 TA'S FROM TCASII AND DID NOT SEE THE TFC. THEN WE GOT AN RA TO CLB. CLBED TO 3400 FT AND WERE THEN INSTRUCTED 'CHK VERT SPD' ON TCASII. WE NEVER DID SEE THE TFC AND ATC DID NOT CALL OUT TFC TO US OR QUERY OUR CLB TO 3400 FT. ON OUR TCASII VERT SPD INDICATOR DISPLAY WE SAW TFC AT 400 FT BELOW US. UPON LNDG AT DFW THE CAPT CALLED ATC ABOUT SITUATION. ATC SAID HE DID NOT SEE CONFLICT BUT WOULD FOLLOW UP ON IT ALSO. COMPANY TCASII PLT/OBSERVER EVENT QUESTIONNAIRE SUBMITTED. MY GUESS IS THAT A VFR TFC NOT IN CTL WITH REQUIRED APCH WAS LEGAL UNDER THE FLOOR OF TCA (3000 MSL). MAYBE AT 2800 FT MSL AND THE TCASII HAD US CLB TO 3400 FT TO GET 500 FT VERT SEPARATION. I FEEL THIS WILL BECOME A COMMON OCCURRENCE. I OWN AN SMA AND FIND IT HARD TO GET CLRED IN TCA SO VFR UNDER IS COMMON FOR GA TO GET AROUND DFW.

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.