TCASII ALTDEV IN HOLDING PATTERN.

Narrative

FLT CMH TO CLT; HOLDING INSTRUCTIONS ISSUED BY ATC CTR TO HOLD AT HMV VOR N 360 DEGS R; 10 MI LEGS R TURNS FL260; EFC XA50 Z. AT APPROX XA47 AND IN ABOUT OUR 3RD TURN INBOUND TO HMZ; TCASII ISSUED TA. WE HAD HEARD ATC INSTRUCTIONS TO INTRUDER ACFT TO DSND TO FL270 TA. TURNED TO RA TO 'DSND' TFC WAS APPROX 800 FT ABOVE US AND DSNDING INTO OUR FLT PATH. I DISENGAGED THE AUTOPLT AND INITIATED DSCNT ACCORDING TO TCASII COMMANDS. AT APPROX FL257; CAPT VISUALLY ACQUIRED INTRUDER TFC AND HALTED DSCNT FOR CONCERN FOR POSSIBLE TFC HOLDING BELOW US. DSCNT HALTED AT APPROX FL256. TCASII INDICATED INTRUDER WAS 800 FT ABOVE US. TCASII WAS STILL ISSUING DSCNT COMMANDS; (AURAL AND VISUAL). INTRUDER THEN WENT BACK TO FL270; AND WE RETURNED TO FL260. CAPT NOTIFIED ATL CTR THAT WE HAD A TCASII DSCNT COMMAND AND DEV. CTR WAS VERY BUSY WITH NUMEROUS OTHER TFC DEVIATING FOR WX AND HOLDING. CONTRIBUTING TO THIS WAS NUMEROUS COMPANY ACFT WITH LIKE CALL SIGNS; SUCH AS ACR XXA; ACR XXC; ACR XXD; ETC. NOTHING WAS MENTIONED BY CTR AS TO OUR ALTDEV TO AVOID INTRUDER ACFT OR TO OTHER ACFT CONCERNING THIS MATTER. WE WERE ISSUED A HDG TO DEPART THE HOLD; THEN SWITCHED TO CLT APCH. SUPPLEMENTAL INFO FROM ACN 274130: AT FL257 I ACQUIRED TFC VISUALLY AND STOPPED ACFT AT FL256. TCASII INDICATED TFC AT 800 FT ABOVE US (FL264). TCASII WAS STILL ISSUING US A MAX DSCNT.