A321
Flight Crew Air Transport Pilot (ATP)
Conflict Airborne Conflict
Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action
Human Factors
During descent into IAH on the DOOBI 2 RNAV arrival; a VFR aircraft flew across our flight path and triggered an ATC traffic alert and a TCAS RA.The VFR aircraft suddenly appeared on our Navigation display.  It was at our current altitude.  We got the ATC traffic alert along with a clearance to turn left immediately to heading 180. Seconds later we got the TCAS RA commanding 'DESCEND; DESCEND'.  We continued the turn while complying with the TCAS RA.  When the TCAS announced 'CLEAR OF CONFLICT'; we reestablished automation and then complied with a new ATC clearance to return to the arrival.  The remainder of the flight was uneventful.I spoke with a representative from Houston TRACON.  She told me that the traffic was being tracked after it departed Galveston; TX. The traffic's transponder was intermittent.  I can confirm that the TCAS TA target appeared suddenly on our displays; suggesting that it had just popped up.  She also said that TRACON was experiencing an increase in VFR traffic failing to use flight following because they don't want have to wait for a climb clearance. This is an issue for Houston TRACON to resolve.  ATC and our TCAS system worked as designed and were the reason we were kept safe.
An A321 Captain experiences a TCAS RA with VFR traffic at 8;000 feet during the DOOBI2 arrival to IAH. The intruder's transponder was intermittent; providing a late TCAS and ATC warning.