ACR X NON ADHERENCE TO ATC CLRNC DSCNT TO WRONG ALT. ALTDEV.

Narrative

I WAS INFORMED APPROX 24 HRS AFTER THE ALLEGED INCIDENT BY FLT MGMNT THAT THE FAA HAD REQUESTED MY CERTIFICATE NUMBER. THE REQUEST WAS DUE TO UNKNOWN REASONS. AFTER QUESTIONING SEVERAL MGRS; I FINALLY FOUND 1 WHO KNOW WHY THE FAA HAD MADE THIS REQUEST. I WAS TOLD THAT I WAS BEING VECTORED FOR A VISUAL APCH TO RWY 9 AT MEM AND CLRED TO 4000 FT MSL AND THAT IT LATER WAS CHANGED TO RWY 36R AND MAINTAIN 7000 FT. THE CTLR SAID THAT WE ONLY 'ROGERED' HIS INSTRUCTIONS. THE WAYS THAT I REMEMBERED THE FLT FROM 10000 FT TILL TOUCHDOWN IS AS FOLLOWS: I HAD BEEN TOLD BY ATC TO EXPECT RWY 9 AND GIVEN A HDG AND DSCNT TO 4000 FT. SOMETIME AFTER THAT; I WAS TOLD THAT THE RWY HAD BEEN CHANGED TO RWY 36R AND GIVEN ANOTHER HDG CHANGE. ALSO I WAS ADVISED OF A ACR Y DC-9 CLBING OUT AT MY 9 O'CLOCK POS. I TOLD THE COPLT TO RPT 'THE TFC IN SIGHT' AND I THOUGHT NOTHING OF IT. I WAS NEVER TOLD THAT I WAS OFF ALT; DSNDING BELOW ASSIGNED ALT OR ANYTHING. IT IS A POSSIBILITY THAT THE CTLR NEVER RECEIVED OUR ACKNOWLEDGMENT OF HIS INSTRUCTIONS. I HAVE BEEN TOLD THAT THE TAPES DO NOT CONTAIN A READBACK FROM MY ACFT ACKNOWLEDGING THE AMENDED ALT OF 7000 FT. (I DON'T THINK IT WAS EVER GIVEN.) SUPPLEMENTAL INFO FROM ACN 298000: WE WERE CLRED BY MEM APCH CTL TO HEAD 150 DEGS FROM GILMORE VOR AND DSND TO 4000 FT FOR A VISUAL APCH TO RWY 9. WE COMPLIED UPON REACHING 4000 FT. WE WERE ADVISED OF DC-9 TFC AT 9 O'CLOCK AND I THINK 4 MI. OUR FO POINTED OUT THE TFC WHICH APPEARED TO BE AT A SAFE DISTANCE AND IN THE CLR. WE CONTINUED OUR APCH AND LANDED ON RWY 36R. I DID NOT HEAR ANY CHANGE IN OUR ALT ASSIGNMENT. I WAS THE SO ON THIS FLT.