Narrative:

At 21 NM, outbound from lfd VOR on the 127 degree radial on the mizar 2 arrival into detroit, confusion over call signs occurred on ATC center frequency. Numerous aircraft were being sequenced for arrival, including our call sign (air carrier xabb) and similar sounding call signs, company xacb and company xadb. Center issued what we thought to be an instruction for company air carrier xabb (us) to descend to 12000 ft and turn to a 30 degree heading. I acknowledged the call, repeating the instructions. The captain initiated the descent. We both remarked that a turn to 30 degrees was not logical at that point in our route. I asked the controller if he had given us a turn to 30 degrees. He stated, 'no you should be on course.' I then asked if he had given us a descent to 12000 ft. He responded, 'no.' the captain immediately returned to FL210. Lowest altitude during the event was 20400 ft indicated altitude. No conflict existed, and the controller apparently was never aware that we had been off the previous altitude. The call signs xabb, xacb, and xadb do not look particularly similar on paper, however, when stated as 'four digit singular numbers pronounced in full' on a crowded frequency, with static and environmental noise present, the potential for mistaken xmissions is high. When such similar call signs are scheduled into a crowded approach corridor simultaneously, the potential for clearance deviations is magnified. Supplemental information from acn 351103: the heading was not logical at this position on the arrival. Normally if ATC needs separation at this point they will slow the aircraft and vector right of course. This error was realized, there was no traffic on TCASII, and ATC made no further comment. I still am not sure whether we answered someone else's radio call and ATC did not correct it with the readback or if ATC mistakenly used our call sign when he intended the call for another aircraft. Callback conversation with reporter revealed the following information: during the previous month and a half, every single time that this flight crew went into dtw, they were met with this same problem. This reporter and first officer were 'laboriously' listening, when this incident occurred. Frequency congestion was so great that reporter captain feels certain the controller did not hear their readback or see their aircraft begin a descent.

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Original NASA ASRS Text

Title: 3 COMPANY ACFT WITH SIMILAR FLT NUMBERS WERE ON THE ARR INTO DTW AT THE SAME TIME. THE RPTING CREW WRONGLY DSNDED AFTER THEY HAD RECEIVED AND READ BACK A CLRNC THAT THEY THOUGHT WAS FOR THEIR AIRPLANE. THE FREQ CONGESTION AND CALL SIGN CONFUSION DURING THE INCIDENT HAS THIS DC9-40 CREW STILL WONDERING IF THE CTLR STATED THE WRONG NUMBER OR IF THEY HAD MISHEARD THE CLRNC.

Narrative: AT 21 NM, OUTBOUND FROM LFD VOR ON THE 127 DEG RADIAL ON THE MIZAR 2 ARR INTO DETROIT, CONFUSION OVER CALL SIGNS OCCURRED ON ATC CTR FREQ. NUMEROUS ACFT WERE BEING SEQUENCED FOR ARR, INCLUDING OUR CALL SIGN (ACR XABB) AND SIMILAR SOUNDING CALL SIGNS, COMPANY XACB AND COMPANY XADB. CTR ISSUED WHAT WE THOUGHT TO BE AN INSTRUCTION FOR COMPANY ACR XABB (US) TO DSND TO 12000 FT AND TURN TO A 30 DEG HDG. I ACKNOWLEDGED THE CALL, REPEATING THE INSTRUCTIONS. THE CAPT INITIATED THE DSCNT. WE BOTH REMARKED THAT A TURN TO 30 DEGS WAS NOT LOGICAL AT THAT POINT IN OUR RTE. I ASKED THE CTLR IF HE HAD GIVEN US A TURN TO 30 DEGS. HE STATED, 'NO YOU SHOULD BE ON COURSE.' I THEN ASKED IF HE HAD GIVEN US A DSCNT TO 12000 FT. HE RESPONDED, 'NO.' THE CAPT IMMEDIATELY RETURNED TO FL210. LOWEST ALT DURING THE EVENT WAS 20400 FT INDICATED ALT. NO CONFLICT EXISTED, AND THE CTLR APPARENTLY WAS NEVER AWARE THAT WE HAD BEEN OFF THE PREVIOUS ALT. THE CALL SIGNS XABB, XACB, AND XADB DO NOT LOOK PARTICULARLY SIMILAR ON PAPER, HOWEVER, WHEN STATED AS 'FOUR DIGIT SINGULAR NUMBERS PRONOUNCED IN FULL' ON A CROWDED FREQ, WITH STATIC AND ENVIRONMENTAL NOISE PRESENT, THE POTENTIAL FOR MISTAKEN XMISSIONS IS HIGH. WHEN SUCH SIMILAR CALL SIGNS ARE SCHEDULED INTO A CROWDED APCH CORRIDOR SIMULTANEOUSLY, THE POTENTIAL FOR CLRNC DEVS IS MAGNIFIED. SUPPLEMENTAL INFO FROM ACN 351103: THE HDG WAS NOT LOGICAL AT THIS POS ON THE ARR. NORMALLY IF ATC NEEDS SEPARATION AT THIS POINT THEY WILL SLOW THE ACFT AND VECTOR R OF COURSE. THIS ERROR WAS REALIZED, THERE WAS NO TFC ON TCASII, AND ATC MADE NO FURTHER COMMENT. I STILL AM NOT SURE WHETHER WE ANSWERED SOMEONE ELSE'S RADIO CALL AND ATC DID NOT CORRECT IT WITH THE READBACK OR IF ATC MISTAKENLY USED OUR CALL SIGN WHEN HE INTENDED THE CALL FOR ANOTHER ACFT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: DURING THE PREVIOUS MONTH AND A HALF, EVERY SINGLE TIME THAT THIS FLC WENT INTO DTW, THEY WERE MET WITH THIS SAME PROB. THIS RPTR AND FO WERE 'LABORIOUSLY' LISTENING, WHEN THIS INCIDENT OCCURRED. FREQ CONGESTION WAS SO GREAT THAT RPTR CAPT FEELS CERTAIN THE CTLR DID NOT HEAR THEIR READBACK OR SEE THEIR ACFT BEGIN A DSCNT.

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.