Narrative:

Air carrier X was at FL350 approximately 80 mi southeast bsr VOR talking to ZOA on 134.55 VMC. Cleared to FL240 280 KTS maximum. I read back clearance and asked for confirmation and controller said yes. Weak radio xmissions on his part. Confirmed by other aircraft on frequency. Started descent approximately 1000 FPM. Some other aircraft said another aircraft answered his clearance. Controller asked air carrier west for his altitude. Some controller confusion as to who was where. At 33700' controller asked my altitude. I said 33700', cleared to FL240. Controller said climb to FL340 70 mi southeast bsr. First officer saw aircraft off right side and low (air carrier Y). Recleared to FL350 by new controller shortly thereafter. After landing I called ZOA by phone. Confusion even then (30 mins later) as to which aircraft was cleared (us or company flight Z). Center said that they would examine date and get back. The next day they found that the clearance was given to the wrong aircraft and that I had responded correctly to center controller. Lessons learned or reinforced: 1) inform any controller of miskeying microphone at beginning or end of transmission. Inform controller of poor quality or unintelligible radio transmission. Misinterpreted clearance should be read and confirmed by both parties (complete call sign and clearance). Use complete call sign in acknowledging. Fortunately I did this and it showed up on tapes. 4) quick response by controller needed if wrong aircraft acknowledges someone elses clearance. Likewise, if someone responds to my clearance. 5) use of similar call signs has been with us for some time and most controllers are good about informing those involved. I've noticed lately that west coast flts are using 4 digit call signs with the first 2 digits being '20'-something, (ie, 2577, 2483, 2679, etc). At times these digits are slurred and if combined with a miskeyed microphone could very easily result in a misinterpreted call sign. If incident data supports that 4 digit call signs are more likely to be involved in safety mishaps, perhaps a new system of call signs could be developed (ie, 2# and a letter). Supplemental information from acn 102820: oak told us to 'turn left heading 270 maintain FL340 immediately.' (our heading at this time was about 300 degrees.) at just the same time I looked to our right and saw air carrier Y passing opp direction approximately 1000' below and 1 NM at our 2 O'clock. I believe this incident highlights the importance of proper radio procedure such as reading back clrncs and using full call signs. Supplemental information from acn 102509: 4 digit call signs are cumbersome and when this is added to trip numbers being similar and in some cases identical, a call sign readback is easy to miss. If air carrier and air taxi company's would cooperate in an effort to solve this dilemma, many situations such as above could be reduced. Increased controller staffing would help. 2 men at a sector leaves the radar controller more time to concentrate on this important subject.

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Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION BETWEEN 2 ACR. OPERATIONAL ERROR. SEE ALSO ACN 102820 AND ACN 102509.

Narrative: ACR X WAS AT FL350 APPROX 80 MI SE BSR VOR TALKING TO ZOA ON 134.55 VMC. CLRED TO FL240 280 KTS MAX. I READ BACK CLRNC AND ASKED FOR CONFIRMATION AND CTLR SAID YES. WEAK RADIO XMISSIONS ON HIS PART. CONFIRMED BY OTHER ACFT ON FREQ. STARTED DSCNT APPROX 1000 FPM. SOME OTHER ACFT SAID ANOTHER ACFT ANSWERED HIS CLRNC. CTLR ASKED ACR W FOR HIS ALT. SOME CTLR CONFUSION AS TO WHO WAS WHERE. AT 33700' CTLR ASKED MY ALT. I SAID 33700', CLRED TO FL240. CTLR SAID CLB TO FL340 70 MI SE BSR. F/O SAW ACFT OFF RIGHT SIDE AND LOW (ACR Y). RECLEARED TO FL350 BY NEW CTLR SHORTLY THEREAFTER. AFTER LNDG I CALLED ZOA BY PHONE. CONFUSION EVEN THEN (30 MINS LATER) AS TO WHICH ACFT WAS CLRED (US OR COMPANY FLT Z). CENTER SAID THAT THEY WOULD EXAMINE DATE AND GET BACK. THE NEXT DAY THEY FOUND THAT THE CLRNC WAS GIVEN TO THE WRONG ACFT AND THAT I HAD RESPONDED CORRECTLY TO CENTER CTLR. LESSONS LEARNED OR REINFORCED: 1) INFORM ANY CTLR OF MISKEYING MIC AT BEGINNING OR END OF XMISSION. INFORM CTLR OF POOR QUALITY OR UNINTELLIGIBLE RADIO XMISSION. MISINTERPRETED CLRNC SHOULD BE READ AND CONFIRMED BY BOTH PARTIES (COMPLETE CALL SIGN AND CLRNC). USE COMPLETE CALL SIGN IN ACKNOWLEDGING. FORTUNATELY I DID THIS AND IT SHOWED UP ON TAPES. 4) QUICK RESPONSE BY CTLR NEEDED IF WRONG ACFT ACKNOWLEDGES SOMEONE ELSES CLRNC. LIKEWISE, IF SOMEONE RESPONDS TO MY CLRNC. 5) USE OF SIMILAR CALL SIGNS HAS BEEN WITH US FOR SOME TIME AND MOST CTLRS ARE GOOD ABOUT INFORMING THOSE INVOLVED. I'VE NOTICED LATELY THAT WEST COAST FLTS ARE USING 4 DIGIT CALL SIGNS WITH THE FIRST 2 DIGITS BEING '20'-SOMETHING, (IE, 2577, 2483, 2679, ETC). AT TIMES THESE DIGITS ARE SLURRED AND IF COMBINED WITH A MISKEYED MIC COULD VERY EASILY RESULT IN A MISINTERPRETED CALL SIGN. IF INCIDENT DATA SUPPORTS THAT 4 DIGIT CALL SIGNS ARE MORE LIKELY TO BE INVOLVED IN SAFETY MISHAPS, PERHAPS A NEW SYSTEM OF CALL SIGNS COULD BE DEVELOPED (IE, 2# AND A LETTER). SUPPLEMENTAL INFO FROM ACN 102820: OAK TOLD US TO 'TURN LEFT HDG 270 MAINTAIN FL340 IMMEDIATELY.' (OUR HDG AT THIS TIME WAS ABOUT 300 DEGS.) AT JUST THE SAME TIME I LOOKED TO OUR RIGHT AND SAW ACR Y PASSING OPP DIRECTION APPROX 1000' BELOW AND 1 NM AT OUR 2 O'CLOCK. I BELIEVE THIS INCIDENT HIGHLIGHTS THE IMPORTANCE OF PROPER RADIO PROC SUCH AS READING BACK CLRNCS AND USING FULL CALL SIGNS. SUPPLEMENTAL INFO FROM ACN 102509: 4 DIGIT CALL SIGNS ARE CUMBERSOME AND WHEN THIS IS ADDED TO TRIP NUMBERS BEING SIMILAR AND IN SOME CASES IDENTICAL, A CALL SIGN READBACK IS EASY TO MISS. IF ACR AND AIR TAXI COMPANY'S WOULD COOPERATE IN AN EFFORT TO SOLVE THIS DILEMMA, MANY SITUATIONS SUCH AS ABOVE COULD BE REDUCED. INCREASED CTLR STAFFING WOULD HELP. 2 MEN AT A SECTOR LEAVES THE RADAR CTLR MORE TIME TO CONCENTRATE ON THIS IMPORTANT SUBJECT.

Data retrieved from NASA's ASRS site as of August 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.