ALTDEV ALT EXCURSION IN FLC RESPONSE TO TCASII RA. RPTR COMPLAINS OF PARACHUTE JUMPING ACTIVITY IN PROX OF APCH RTE AND THE IMPROPER ALT USED BY THOSE JUMP ACFT.

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INBOUND TO DFW ON THE SCURRY ARR APCHING SEAGO INTXN IN A DSCNT APCHING 11000 FT; A TCASII ADVISORY OCCURRED ON A TARGET AT 12 O'CLOCK CLBING. AT 11200 FT THE ADVISORY SWITCHED TO AN RA COMMANDING A CLB GREATER THEN 200 FPM. WE RESPONDED BY CLBING IMMEDIATELY TO 12000 FT WHICH COINCIDED WITH CONFLICT RESOLUTION. THE TARGET PASSED APPROX 1 MI OFF THE R SIDE OF OUR ACFT. VISUAL CONTACT WAS NEVER MADE. THE MINIMUM SEPARATION INDICATED BY TCASII WAS 200 FT. DURING THE EVENT; THE OTHER ACFT WAS A LIGHT ACFT CARRYING PARACHUTE JUMPERS. HE WAS IN CONTACT WITH DFW APCH CTL. WE DID NOT RECEIVE ANY TA'S PRIOR TO OR DURING THIS EVENT. WHEN WE ADVISED ATC THAT WE WERE CLBING IN RESPONSE TO A TCASII RA; THE CTLR IMMEDIATELY QUERIED THE LIGHT ACFT ABOUT HIS ALT. THE LIGHT ACFT SAID THAT HE WAS AT 10800 FT AND WAS DSNDING BACK DOWN TO HIS ASSIGNED ALT OF 10500. HUMAN FACTORS CONSIDERATION: FLYING REGULARLY INTO DFW TENDS TO LEAD A CREW INTO THE MODE OF EXPECTING THE DALLAS 'BUMP-UP' PHENOMENON. TCASII TA'S OFTEN OCCUR IN THIS AREA. WE ASSUMED INITIALLY THAT THIS PARTICULAR TA WAS AN ACFT ON A DFW DEP. SUPPLEMENTAL INFO FROM ACN 261129: SINCE THE ABNORMAL (A TA) IS NORMAL HERE; IT CAN SLOW REACTION TIME AND OR LULL THE PLT WITH A FALSE SENSE OF SECURITY. SINCE DFW DEPS ARE AT 10000; I DO NOT THINK IT SAFE FOR SKYDIVERS JUMPING AT 10500. FURTHER; THERE SHOULD BE NO TFC AT 10500 FT. ALTIMETER ERROR OR SLIGHTEST ALTDEV GIVES UNACCEPTABLE SEPARATION.