Narrative:

I was en route on a lifeguard priority flight at FL180. After transmitting an MOA, with the controling facility, I was handed off to center. Establishing initial contact was normal. Due to my nearness to my destination, I requested a lower altitude the controller then cleared me down to 10000 ft, I informed the controller that I was leaving FL180 for 10000 ft, and repeated my number. Passing through 17000 ft the controller told me to climb and maintain FL180. I then climbed back to 18000 ft. The controller informed me that he did not clear me to descend. I told him that he did, in fact, clear me down to 10000 ft, and that I read back the clearance to him. The controller said that the clearance was for another lifeguard flight, and that I should 'listen better.' at the time, I was wearing a good quality headset and had no difficulty hearing any other controllers. The tail number of the other lifeguard aircraft 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 altitude may have put my tail number in his mind and he may have inadvertently said my number for the other aircraft. Callback conversation with reporter revealed the following information: reporter states he was very close to destination and needed to descend. No frequency congestion to confuse. Did complete readback. Call sign similarities, 1t2 vs 11T, but both lifeguard flts, which may have created the communication problem for controller and reporter.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.