MD90 FLC STOPPED CLBING AND DSNDED IN RESPONSE TO A TCASII RA CAUSING A CABIN ATTENDANT AND A PAX AIR SICKNESS WHEREIN THE PAX STAYED IN THE LAVATORY DURING LNDG.

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IT WAS A BEAUTIFUL CLR VFR DAY; UNLIMITED VISIBILITY. MY FO WAS THE PF. WE RECEIVED 3 ALT CLRNC CHANGES IN THE FIRST 3 MINS PRIOR TO THE RA. PRIOR TO TKOF; OUR ORIGINAL CLRNC WAS TO FLY THE POMONA 6 DEP AND CLB TO 14000 FT. WHEN CLRED FOR TKOF BY ONT TWR; WE WERE TOLD TO LEVEL AT 5000 FT. ACARS LIFTOFF TIME WAS XA59Z. CONTACTED SOCAL DEP ON 125.5. THEY POINTED OUT NUMEROUS TARGETS AND HAD US MAINTAIN A 255 DEG HDG INSTEAD OF INTERCEPTING THE POMONA 6. WE SAW SOME TFC AND HAD OTHERS ON TCASII WITHOUT TA ALERTS. NEXT CLRNC WAS TO CLB TO 7000 FT; TURN TO 270 DEGS AND CONTACT DEP ON XX. AFTER CHKING IN ON THE NEW FREQ WE WERE TOLD TO LEVEL AT 5000 FT. AT THE TIME WE WERE IN A CLB PASSING 4500 FT. WE GOT IT LEVEL AT 5000 FT WITH AUTOPLT ENGAGED FO THE PF. MORE TFC POINTED OUT AND CLB CLRNC TO 14000 FT ALONG WITH AT TURN TO 320 DEGS TO INTERCEPT THE POM 301 DEG RADIAL AND DAGGET TRANSITION WAS ISSUED. IT WAS IN THIS CLB AT ABOUT XA03Z AS WE WERE BTWN 5000 FT AND 6500 FT THAT AN RA OF 'DSND' WAS COMMANDED BY TCASII. OUR RATE OF CLB WAS APPROX +2000 FPM. I SAW THE RED TARGET ON TCASII AT +05 (RED) THE VSI WAS ALL RED ARC EXCEPT FOR THE SMALL GREEN ARC IN THE 1000-1500 F-PM DOWN RANGE. THE ACFT WAS ON AUTOPLT DFCG #2. FO LOOKED OUT AND HAD A VISUAL ON WHAT APPEARED TO BE THE RA TFC. IT WAS A SINGLE ENG LOW WING LIGHT ACFT IN WHAT APPEARED TO BE LEVEL FLT. I DECIDED TO TAKE THE ACFT AND FLY THE TCASII COMMANDS. I DISCONNECTED THE AUTOPLT AND PUSHED OVER. WE WENT FROM +2000 FPM TO -1000 FPM IN A FEW MOMENTS. WE WERE AT LESS THAN +1G IN THE PUSHOVER. I NEVER SAW THE RA TFC. THE FO HAD THE ACFT IN SIGHT AND SAID IT APPEARED TO BE LESS THAN 2 MI AWAY. TCASII SHOWED IT AROUND THE INNER RING. I MADE A PA DESCRIBING THE EVENT AS A TCASII DIRECTED MANEUVER TO AVOID A TFC CONFLICT WITH A BIT OF A DESCRIPTION OF THE TCASII SYS AND ITS FUNCTION. NO INJURIES WERE RPTED BY PAX OR CREW. ON ARR; I INFORMED THE GATE AGENT TO BE AWARE THAT SOME PAX MIGHT BE UPSET AFTER DEPLANING BECAUSE OF OUR TCASII MANEUVER. I CALLED THE OCC TO INFORM OUR DUTY PLT. HE GOT ME THE SOCAL PHONE NUMBER. I TALKED WITH A CTLR ABOUT THE EVENT. HE SAID THE TFC WAS POP-UP VFR AT 6500 FT AND SORRY. I INFORMED HIM THAT WE WERE NOT FILING AN NMAC RPT AS PER OUR FOM DIRECTIONS. A FLT ATTENDANT SUPVR IN SLC CAME DOWN TO OUR GATE TO TALK WITH ME ABOUT THE INCIDENT BECAUSE OF A FLT ATTENDANT COMPLAINT ABOUT HER FEAR OF FLYING. ALSO REMARKABLE IS THAT INSIDE 3 MI FROM LNDG A FLT ATTENDANT CALLED TO INFORM US THERE WAS A WOMAN IN THE AFT LAVATORY GETTING SICK THAT REFUSED TO COME OUT. I DECIDED RATHER THAN GOING AROUND AND TRYING TO GET HER BACK TO HER SEAT IT WOULD BE BETTER TO LAND. I DIRECTED THE FLT ATTENDANT TO TELL THIS PAX TO REMAIN IN THE LAVATORY UNTIL WE TELL HER SHE CAN COME OUT AFTER LNDG.