Narrative:

I was working R31 at XA15 pm, 4/thurs/88. Medium large transport Y was a rno departure going to sfo. He was cleared ila-eni-pye-sfo at FL260. After medium large transport Y passed ila, I cleared him direct pye for sequencing into sfo. I had 2 XXXX airline flts on frequency, medium large transport xyx, sfo direct rbl and medium large transport abx sjc direct rbl. On initial call I climbed medium large transport abx to FL280, he requested FL310, but I was unable to do that because of same direction traffic at FL310, a ZZZZ airlines flight. On initial call I climbed medium large transport xyx to FL250. He requested higher, but I was unable to climb him higher due to traffic at FL260, which was medium large transport Y. I told medium large transport xyx to expect higher in 3 mins, then I corrected that and said in 5 mins. Medium large transport xyx was then 10-15 mi away from medium large transport Y. I meant to call medium large transport abx to tell him to climb to FL290, but I mistakenly called medium large transport agx, who was not on frequency, to climb to FL290. Medium large transport xyx took the clearance for medium large transport agx and responded, 'medium large transport xyx maintain FL290.' I did not catch the fact that medium large transport xyx answered by mistake. I had the j-ring circle on medium large transport Y, so when I had 5 mi sep with medium large transport xyx, I could climb medium large transport xyx. Medium large transport Y's data block showed level at FL260. Medium large transport xyx data block showed a temporary altitude of FL250 and the mode C showed level at FL250. Now both targets were within the j-ring circle and I saw medium large transport xyx at FL254, 400' high. I asked medium large transport xyx his altitude, believing the 400' was a bad mode C hit by the radar. Medium large transport xyx answered 'climbing to FL290.' I told him he was not assigned above FL250. He answered that he would descend back to FL250. After medium large transport xyx said he would go back down to FL250, the 2 aircraft had passed by 5 mi and sep was increasing. No further action was taken. The sector was becoming very busy with the departures going northbound leaving oak, sfo and sjc. The medium large transport Y was traffic for the sfo and oak departures. The sjc departures are far enough south to easily top medium large transport Y at FL260. I was given 3 aircraft well south of medium large transport Y (30-40 mi) on parallel or near parallel headings going northbound. These do not include medium large transport xyx, who was within 20 mi of medium large transport Y or medium large transport abx, who was 50-60 mi away from medium large transport Y. The 3 aircraft from the south were climbing to FL240 or 250 from a lower altitude sector. I was not talking to these aircraft when I made decisions concerning the sequencing and sep of my sector. Medium large transport Y requested lower altitude due to a bad ride at FL260. I looked at the situation with the 3 aircraft to the south of medium large transport Y and I believed medium large transport Y could probably get to FL240 and the 3 aircraft could climb above FL250 in plenty of time to ensure sep. Medium large transport Y was still proceeding direct eni at this time, having passed ila. The sequence for sfo was such that medium large transport Y was following a BBBB flight and leading a ZZZZ flight. I decided to send medium large transport Y direct pye to help the sequencing for sfo. If I had not sent medium large transport Y direct pye, this would have forced the ZZZZ flight to stay on a vector for spacing longer than needed. Turning medium large transport Y direct pye turned him into medium large transport xyx, which made it impossible to descend him below FL260. It also made it impossible to climb medium large transport xyx. The 3 aircraft from the south of medium large transport Y also could then go no higher than FL250 until passing medium large transport xyx. I don't know where this goes. After medium large transport xyx read back the incorrect clearance, I turned him to a heading of 360 degrees. This had nothing to do with trying to maintain sep with medium large transport Y, as I thought medium large transport xyx was still assigned FL250. I gave medium large transport xyx this vector for spacing, so that medium large transport xyx would be clear of medium large transport Y sooner. The error occurred because I thought I heard medium large transport abx respond to medium large transport agx's clearance and because medium large transport xyx thought he heard medium large transport xyx's call sign when in fact he heard medium large transport agx's. Remember, I said medium large transport agx incorrectly. Why I said medium large transport agx instead of medium large transport abx, I don't know. In conclusion, medium large transport xyx heard what he wanted to hear, I heard what I wanted to hear and both of us heard something entirely different. One area to look into is what numbers sound alike--does medium large transport xyx sound like medium large transport agx? Does medium large transport abx sound like medium large transport xyx? The most important point here is they both end in X's. Is the last number the one that people key into? Would medium large transport xyx sound like medium large transport xyw? If medium large transport xyx is listening for the X, such as medium large transport agx ends in,would medium large transport xyw just pass by him and get no response.

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Original NASA ASRS Text

Title: CTLR MISSPOKE SIMILAR SOUNDING CALL SIGNS AND FLT CREW TOOK CLIMB MEANT FOR ANOTHER FLT, RESULTING IN LESS THAN STANDARD SEPARATION.

Narrative: I WAS WORKING R31 AT XA15 PM, 4/THURS/88. MLG Y WAS A RNO DEP GOING TO SFO. HE WAS CLRED ILA-ENI-PYE-SFO AT FL260. AFTER MLG Y PASSED ILA, I CLRED HIM DIRECT PYE FOR SEQUENCING INTO SFO. I HAD 2 XXXX AIRLINE FLTS ON FREQ, MLG XYX, SFO DIRECT RBL AND MLG ABX SJC DIRECT RBL. ON INITIAL CALL I CLBED MLG ABX TO FL280, HE REQUESTED FL310, BUT I WAS UNABLE TO DO THAT BECAUSE OF SAME DIRECTION TFC AT FL310, A ZZZZ AIRLINES FLT. ON INITIAL CALL I CLBED MLG XYX TO FL250. HE REQUESTED HIGHER, BUT I WAS UNABLE TO CLB HIM HIGHER DUE TO TFC AT FL260, WHICH WAS MLG Y. I TOLD MLG XYX TO EXPECT HIGHER IN 3 MINS, THEN I CORRECTED THAT AND SAID IN 5 MINS. MLG XYX WAS THEN 10-15 MI AWAY FROM MLG Y. I MEANT TO CALL MLG ABX TO TELL HIM TO CLB TO FL290, BUT I MISTAKENLY CALLED MLG AGX, WHO WAS NOT ON FREQ, TO CLB TO FL290. MLG XYX TOOK THE CLRNC FOR MLG AGX AND RESPONDED, 'MLG XYX MAINTAIN FL290.' I DID NOT CATCH THE FACT THAT MLG XYX ANSWERED BY MISTAKE. I HAD THE J-RING CIRCLE ON MLG Y, SO WHEN I HAD 5 MI SEP WITH MLG XYX, I COULD CLB MLG XYX. MLG Y'S DATA BLOCK SHOWED LEVEL AT FL260. MLG XYX DATA BLOCK SHOWED A TEMPORARY ALT OF FL250 AND THE MODE C SHOWED LEVEL AT FL250. NOW BOTH TARGETS WERE WITHIN THE J-RING CIRCLE AND I SAW MLG XYX AT FL254, 400' HIGH. I ASKED MLG XYX HIS ALT, BELIEVING THE 400' WAS A BAD MODE C HIT BY THE RADAR. MLG XYX ANSWERED 'CLBING TO FL290.' I TOLD HIM HE WAS NOT ASSIGNED ABOVE FL250. HE ANSWERED THAT HE WOULD DSND BACK TO FL250. AFTER MLG XYX SAID HE WOULD GO BACK DOWN TO FL250, THE 2 ACFT HAD PASSED BY 5 MI AND SEP WAS INCREASING. NO FURTHER ACTION WAS TAKEN. THE SECTOR WAS BECOMING VERY BUSY WITH THE DEPS GOING NBOUND LEAVING OAK, SFO AND SJC. THE MLG Y WAS TFC FOR THE SFO AND OAK DEPS. THE SJC DEPS ARE FAR ENOUGH S TO EASILY TOP MLG Y AT FL260. I WAS GIVEN 3 ACFT WELL S OF MLG Y (30-40 MI) ON PARALLEL OR NEAR PARALLEL HDGS GOING NBND. THESE DO NOT INCLUDE MLG XYX, WHO WAS WITHIN 20 MI OF MLG Y OR MLG ABX, WHO WAS 50-60 MI AWAY FROM MLG Y. THE 3 ACFT FROM THE S WERE CLBING TO FL240 OR 250 FROM A LOWER ALT SECTOR. I WAS NOT TALKING TO THESE ACFT WHEN I MADE DECISIONS CONCERNING THE SEQUENCING AND SEP OF MY SECTOR. MLG Y REQUESTED LOWER ALT DUE TO A BAD RIDE AT FL260. I LOOKED AT THE SITUATION WITH THE 3 ACFT TO THE S OF MLG Y AND I BELIEVED MLG Y COULD PROBABLY GET TO FL240 AND THE 3 ACFT COULD CLB ABOVE FL250 IN PLENTY OF TIME TO ENSURE SEP. MLG Y WAS STILL PROCEEDING DIRECT ENI AT THIS TIME, HAVING PASSED ILA. THE SEQUENCE FOR SFO WAS SUCH THAT MLG Y WAS FOLLOWING A BBBB FLT AND LEADING A ZZZZ FLT. I DECIDED TO SEND MLG Y DIRECT PYE TO HELP THE SEQUENCING FOR SFO. IF I HAD NOT SENT MLG Y DIRECT PYE, THIS WOULD HAVE FORCED THE ZZZZ FLT TO STAY ON A VECTOR FOR SPACING LONGER THAN NEEDED. TURNING MLG Y DIRECT PYE TURNED HIM INTO MLG XYX, WHICH MADE IT IMPOSSIBLE TO DSND HIM BELOW FL260. IT ALSO MADE IT IMPOSSIBLE TO CLB MLG XYX. THE 3 ACFT FROM THE S OF MLG Y ALSO COULD THEN GO NO HIGHER THAN FL250 UNTIL PASSING MLG XYX. I DON'T KNOW WHERE THIS GOES. AFTER MLG XYX READ BACK THE INCORRECT CLRNC, I TURNED HIM TO A HDG OF 360 DEGS. THIS HAD NOTHING TO DO WITH TRYING TO MAINTAIN SEP WITH MLG Y, AS I THOUGHT MLG XYX WAS STILL ASSIGNED FL250. I GAVE MLG XYX THIS VECTOR FOR SPACING, SO THAT MLG XYX WOULD BE CLR OF MLG Y SOONER. THE ERROR OCCURRED BECAUSE I THOUGHT I HEARD MLG ABX RESPOND TO MLG AGX'S CLRNC AND BECAUSE MLG XYX THOUGHT HE HEARD MLG XYX'S CALL SIGN WHEN IN FACT HE HEARD MLG AGX'S. REMEMBER, I SAID MLG AGX INCORRECTLY. WHY I SAID MLG AGX INSTEAD OF MLG ABX, I DON'T KNOW. IN CONCLUSION, MLG XYX HEARD WHAT HE WANTED TO HEAR, I HEARD WHAT I WANTED TO HEAR AND BOTH OF US HEARD SOMETHING ENTIRELY DIFFERENT. ONE AREA TO LOOK INTO IS WHAT NUMBERS SOUND ALIKE--DOES MLG XYX SOUND LIKE MLG AGX? DOES MLG ABX SOUND LIKE MLG XYX? THE MOST IMPORTANT POINT HERE IS THEY BOTH END IN X'S. IS THE LAST NUMBER THE ONE THAT PEOPLE KEY INTO? WOULD MLG XYX SOUND LIKE MLG XYW? IF MLG XYX IS LISTENING FOR THE X, SUCH AS MLG AGX ENDS IN,WOULD MLG XYW JUST PASS BY HIM AND GET NO RESPONSE.

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.