SPS IS A DUAL USE (CIVILIAN-MIL) ARPT. RPTR STATES WHILE MAKING AN APCH TO RWY 17 IN AN ACR; THE CREW RECEIVED A TCASII RA INDICATING CLB. WHILE THE CAPT IS RESPONDING TO THE RA; THE FO SPOTS A T38 ABOVE IN A TURN AND CLAIMS THAT ACFT AND OTHER T38'S ARE IN A CLOSED PATTERN (POSSIBLY TO ANOTHER RWY) WITH THEIR XPONDERS ON STANDBY. HE BELIEVES THERE IS A POSSIBILITY THAT IN RESPONDING TO A TCASII ALERT; A FLT COULD CONFLICT WITH AN ACFT OPERATING A XPONDER ON STANDBY.

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DURING ARR TO RWY 17 AT SPS; WE HEARD APCH CTL WORKING A T38 INBOUND TO A VFR DOWNWIND ENTRY POINT NEAR OUR ENTRY POINT (SPS VORTAC). APCH CTL SEQUENCED THE T38 BEHIND US AND SENT US TO TWR. SHORTLY AFTER THAT; TCASII ISSUED A XING CLB RA. AS THE CAPT (PF) RESPONDED TO THE RA; I STARTED TO ADVISE TWR AND SIMULTANEOUSLY ACQUIRED THE T38 AT 4-5 O'CLOCK AND SLIGHTLY HIGH; TURNING N BEHIND US. THE REST OF APCH AND LNDG WERE UNEVENTFUL. WHAT BOTHERS ME MOST ABOUT THIS SIT IS THAT; IN RESPONDING TO THE RA; WE COULD HAVE CLBED INTO OTHER T38'S IN THE CLOSED OR 'INSIDE DOWNWIND.' THESE ACFT ESTABLISHED IN THE VFR PATTERN SQUAWK STANDBY TO PRECLUDE RADAR CLUTTER; AND ARE NOT IN RADIO CONTACT WITH TWR OR ANY OTHER ATC AGENCY. THE COMMERCIAL CHART PAGES ON THE ARR PROC ARE ONLY THE TIP OF THE ICEBERG. THERE IS LOTS OF POTENTIAL FOR DISASTER FOR ANYONE OPERATING AT SPS WITHOUT DETAILED AWARENESS OF HOW THE LCL TFC OPERATES. FLC SUBMITTED A COMPANY DEBRIEF WITH A RECOMMENDATION TO PUBLICIZE THIS INCIDENT TO ALL PLT GROUP PLTS.