Narrative:

While proceeding direct slugg intersection on the slugg 5 arrival into dto at FL210; we were given a pilot's discretion clearance by ZFW to 15000 ft and to expect clearance to cross slugg at 4000 ft. Ftw told us to begin descent at the same time we calculated we should begin descent to make the expected crossing restr. Prior to reaching 15000 ft; the captain (PF) and myself performing copilot duties (PNF) both copied and I read back a clearance from ftw for us to descend to 6000 ft. I then asked ATC to reconfirm the descent for aircraft X since we were given traffic off to our right at 14000 ft. We both understood ATC to reconfirm our clearance to 6000 ft assignment. At that point; I was thinking that maybe the other traffic; which I think was a king air; was VFR and either climbing or descending through 14000 ft and that the traffic callout was advisory only. While descending at 2000 FPM to comply with the expected crossing restr and passing through 14300 ft; ATC told us to maintain 15000 ft which was impossible at that point. We were already through 14000 ft for 6000 ft. We told ATC of our situation and quizzed him again about our previously understood clearance to 6000 ft. The ATC controller denied giving us 6000 ft and said the 6000 ft assignment was for another aircraft whose tail number I did not learn other than it ended with a discrete suffix. Neither of us heard any clearance for such a tail number. We did acquire the other aircraft visually when passing through about 14000 ft and separation did not seem very close. I'm quite certain that frequency blockage at a very inopportune time was the root cause of this assumed altitude deviation. In addition; a similar sounding call sign caution alert was not provided to us by ATC which is normally provided; was likely a contributing factor. The captain and I consider ourselves professional pilots and we regret the misunderstanding and loss of separation. We are not in the habit of disregarding clrncs. Frequency congestion; blocked xmissions and similar call signs just don't mix in the ATC environment today and a remedy needs to be found soon.

Related reports:

Google
 

Original NASA ASRS Text

Title: SW3 FLT CREW WITH ZFW AT APPROX 140000 FT EXPERIENCED CONFLICT BECAUSE OF UNAUTH DSCNT WHEN CLRNC WAS ISSUED TO SIMILAR SOUNDING ACFT IDENT.

Narrative: WHILE PROCEEDING DIRECT SLUGG INTXN ON THE SLUGG 5 ARR INTO DTO AT FL210; WE WERE GIVEN A PLT'S DISCRETION CLRNC BY ZFW TO 15000 FT AND TO EXPECT CLRNC TO CROSS SLUGG AT 4000 FT. FTW TOLD US TO BEGIN DSCNT AT THE SAME TIME WE CALCULATED WE SHOULD BEGIN DSCNT TO MAKE THE EXPECTED XING RESTR. PRIOR TO REACHING 15000 FT; THE CAPT (PF) AND MYSELF PERFORMING COPLT DUTIES (PNF) BOTH COPIED AND I READ BACK A CLRNC FROM FTW FOR US TO DSND TO 6000 FT. I THEN ASKED ATC TO RECONFIRM THE DSCNT FOR ACFT X SINCE WE WERE GIVEN TFC OFF TO OUR R AT 14000 FT. WE BOTH UNDERSTOOD ATC TO RECONFIRM OUR CLRNC TO 6000 FT ASSIGNMENT. AT THAT POINT; I WAS THINKING THAT MAYBE THE OTHER TFC; WHICH I THINK WAS A KING AIR; WAS VFR AND EITHER CLBING OR DSNDING THROUGH 14000 FT AND THAT THE TFC CALLOUT WAS ADVISORY ONLY. WHILE DSNDING AT 2000 FPM TO COMPLY WITH THE EXPECTED XING RESTR AND PASSING THROUGH 14300 FT; ATC TOLD US TO MAINTAIN 15000 FT WHICH WAS IMPOSSIBLE AT THAT POINT. WE WERE ALREADY THROUGH 14000 FT FOR 6000 FT. WE TOLD ATC OF OUR SIT AND QUIZZED HIM AGAIN ABOUT OUR PREVIOUSLY UNDERSTOOD CLRNC TO 6000 FT. THE ATC CTLR DENIED GIVING US 6000 FT AND SAID THE 6000 FT ASSIGNMENT WAS FOR ANOTHER ACFT WHOSE TAIL NUMBER I DID NOT LEARN OTHER THAN IT ENDED WITH A DISCRETE SUFFIX. NEITHER OF US HEARD ANY CLRNC FOR SUCH A TAIL NUMBER. WE DID ACQUIRE THE OTHER ACFT VISUALLY WHEN PASSING THROUGH ABOUT 14000 FT AND SEPARATION DID NOT SEEM VERY CLOSE. I'M QUITE CERTAIN THAT FREQ BLOCKAGE AT A VERY INOPPORTUNE TIME WAS THE ROOT CAUSE OF THIS ASSUMED ALTDEV. IN ADDITION; A SIMILAR SOUNDING CALL SIGN CAUTION ALERT WAS NOT PROVIDED TO US BY ATC WHICH IS NORMALLY PROVIDED; WAS LIKELY A CONTRIBUTING FACTOR. THE CAPT AND I CONSIDER OURSELVES PROFESSIONAL PLTS AND WE REGRET THE MISUNDERSTANDING AND LOSS OF SEPARATION. WE ARE NOT IN THE HABIT OF DISREGARDING CLRNCS. FREQ CONGESTION; BLOCKED XMISSIONS AND SIMILAR CALL SIGNS JUST DON'T MIX IN THE ATC ENVIRONMENT TODAY AND A REMEDY NEEDS TO BE FOUND SOON.

Data retrieved from NASA's ASRS site as of January 2009 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.