FLC RESPONDED TO TCASII RA WITH A DSCNT OF 2000 FPM AS COMMANDED.

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IAH TO ELP. DEPART IAH AT XA50 LCL TIME. CLBING OUT OF 12000 FT MSL; GOING TO FL230; WE HAD JUST BEEN SWITCHED FROM 123.8 (HOUSTON DEP CTL) TO 132.15 (ZHU); WHEN WE RECEIVED A HARD TCASII (RA). WE WERE ON THE HUMBLE (116.6) 272 DEG RADIAL; 30 DME; ON J-86. WE FOLLOWED THE RA AT 2000 FPM AND DSNDED TO 11000 FT MSL. THE RA WAS LESS THAN 2 MI AWAY AT 9 O'CLOCK POS. WE ADVISED ZHU ON 132.15 OF THE RA AND THEY SAID THAT THEY SHOWED NOTHING ON THEIR SCOPE. 5 SECONDS LATER; CTR INFORMED US THAT IT WAS A VFR ACFT WITH A SQUAWK ASSIGNED BY APCH CTL AND CTR 'WONDERED WHY APCH CTL HAD SWITCHED US OVER TO CTR FREQ WHEN THERE WAS TFC TO BE POINTED-OUT TO US BY APCH CTL.' NEITHER CTR; NOR OUR ACFT KNEW OF THE TFC WHICH APCH CTL WAS 'WORKING.' LATER (48 MINS); AT XB38 LCL WE CALLED CTR AGAIN ON 132.15 AND THEY INFORMED US THAT 'THERE WAS NO PROB WITH OUR ALTDEV.' ZHU HAD BEEN UNABLE FOR 20 MINS TO GET APCH CTL TO ACKNOWLEDGE HOW THIS HAD HAPPENED. THERE WERE NO INJURIES TO PAX OR CREW. FLT CONTINUED UNEVENTFULLY TO ELP. IT APPEARS THAT APCH CTL FORGOT TO TELL US OF THE TFC AND THEN SWITCHED US TO CTR FREQ.