AIR AMB ON SAME FREQ AS A SECOND AIR AMB; ISSUED CLRNC TO DSND. TOLD CLRNC NOT FOR HIM AFTER DSCNT STARTED.

Narrative

I WAS ENRTE ON A LIFEGUARD PRIORITY FLT AT FL180. AFTER XMITTING AN MOA; WITH THE CTLING FACILITY; I WAS HANDED OFF TO CTR. ESTABLISHING INITIAL CONTACT WAS NORMAL. DUE TO MY NEARNESS TO MY DEST; I REQUESTED A LOWER ALT THE CTLR THEN CLRED ME DOWN TO 10000 FT; I INFORMED THE CTLR THAT I WAS LEAVING FL180 FOR 10000 FT; AND REPEATED MY NUMBER. PASSING THROUGH 17000 FT THE CTLR TOLD ME TO CLB AND MAINTAIN FL180. I THEN CLBED BACK TO 18000 FT. THE CTLR INFORMED ME THAT HE DID NOT CLR ME TO DSND. I TOLD HIM THAT HE DID; IN FACT; CLR ME DOWN TO 10000 FT; AND THAT I READ BACK THE CLRNC TO HIM. THE CTLR SAID THAT THE CLRNC WAS FOR ANOTHER LIFEGUARD FLT; AND THAT I SHOULD 'LISTEN BETTER.' AT THE TIME; I WAS WEARING A GOOD QUALITY HEADSET AND HAD NO DIFFICULTY HEARING ANY OTHER CTLRS. THE TAIL NUMBER OF THE OTHER LIFEGUARD ACFT HAD SOME SIMILARITIES; BUT NOT ENOUGH TO MISTAKE ONE FOR THE OTHER. I THINK A POSSIBLE FACTOR COULD HAVE BEEN THAT BY REQUESTING A LOWER ALT MAY HAVE PUT MY TAIL NUMBER IN HIS MIND AND HE MAY HAVE INADVERTENTLY SAID MY NUMBER FOR THE OTHER ACFT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES HE WAS VERY CLOSE TO DEST AND NEEDED TO DSND. NO FREQ CONGESTION TO CONFUSE. DID COMPLETE READBACK. CALL SIGN SIMILARITIES; 1T2 VS 11T; BUT BOTH LIFEGUARD FLTS; WHICH MAY HAVE CREATED THE COM PROBLEM FOR CTLR AND RPTR.