Narrative:

Aircraft X sebound at FL330 route tvc fnt lck. Aircraft Y nwbound at FL350 on spacing vector from route fnt J94 pmm. An additional 20 aircraft on frequency. Traffic level considered to be complex. Aircraft B was issued 'direct pmm' (a left turn to approximately 250 degree) and a descent clearance to FL310. X checks in on frequency while controller is off frequency. Coordinating other flight information with my adjacent airspace controller. Controller realizes that X and Y are a potential conflict and attempts to contact X with the intent to issue a 20 degree left turn to vector X east and behind Y that is descending and turning west. The call sign of X is unfamiliar to controller, so controller calls X, speaking the call letters phonetically. Receiving no response, and realizing that X has just recently entered the sector's airspace the controller goes off frequency to contact previous sector controller to see if X is still in communication with previous controller. X again attempts to establish initial contact while controller is off frequency but the call is not heard by controller. The controller again speaks X call sign phonetically to previous controller who responds 'I put him on you, he's not here.' at this time the conflict alert activates. Controller asks Y to expedite rate of descent for traffic then calls X 3 times phonetically before X pilot responds. X is instructed to turn approximately 75 degree to the left immediately. Y is instructed to increase rate of descent and report reaching FL310. X is cleared to climb to FL350 and report leaving FL335. When the aircraft were 4.687 mi apart the mode C altitudes were X 331 and Y 315 resulting in 1600 vertical ft of separation. After thorough review it was determined that the speaker where radio xmissions from aircraft are routed to when a controller leaves the frequency to use a 'land-line' to coordination with a controller at another sector/facility, (which is called option 'X') was in fact disconnected/broken thus controller would never have heard X transmissions. Nearly 3 mins elapsed from the initial attempt by X to contact the controller and the resulting loss of separation. Suggestion to avoid similar problems. Foreign air carriers, new carriers/ call signs or air carrier/taxi operations entering new service areas have call signs noted in remarks section of flight plan. Secondly perhaps an indicator light could be installed to indicate that option 'X' speaker/circuit is operational.

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Original NASA ASRS Text

Title: ACFT X HAD LTSS FROM ACFT Y. SYS ERROR.

Narrative: ACFT X SEBOUND AT FL330 RTE TVC FNT LCK. ACFT Y NWBOUND AT FL350 ON SPACING VECTOR FROM RTE FNT J94 PMM. AN ADDITIONAL 20 ACFT ON FREQ. TFC LEVEL CONSIDERED TO BE COMPLEX. ACFT B WAS ISSUED 'DIRECT PMM' (A L TURN TO APPROX 250 DEG) AND A DSCNT CLRNC TO FL310. X CHKS IN ON FREQ WHILE CTLR IS OFF FREQ. COORDINATING OTHER FLT INFO WITH MY ADJACENT AIRSPACE CTLR. CTLR REALIZES THAT X AND Y ARE A POTENTIAL CONFLICT AND ATTEMPTS TO CONTACT X WITH THE INTENT TO ISSUE A 20 DEG L TURN TO VECTOR X E AND BEHIND Y THAT IS DSNDING AND TURNING W. THE CALL SIGN OF X IS UNFAMILIAR TO CTLR, SO CTLR CALLS X, SPEAKING THE CALL LETTERS PHONETICALLY. RECEIVING NO RESPONSE, AND REALIZING THAT X HAS JUST RECENTLY ENTERED THE SECTOR'S AIRSPACE THE CTLR GOES OFF FREQ TO CONTACT PREVIOUS SECTOR CTLR TO SEE IF X IS STILL IN COM WITH PREVIOUS CTLR. X AGAIN ATTEMPTS TO ESTABLISH INITIAL CONTACT WHILE CTLR IS OFF FREQ BUT THE CALL IS NOT HEARD BY CTLR. THE CTLR AGAIN SPEAKS X CALL SIGN PHONETICALLY TO PREVIOUS CTLR WHO RESPONDS 'I PUT HIM ON YOU, HE'S NOT HERE.' AT THIS TIME THE CONFLICT ALERT ACTIVATES. CTLR ASKS Y TO EXPEDITE RATE OF DSCNT FOR TFC THEN CALLS X 3 TIMES PHONETICALLY BEFORE X PLT RESPONDS. X IS INSTRUCTED TO TURN APPROX 75 DEG TO THE L IMMEDIATELY. Y IS INSTRUCTED TO INCREASE RATE OF DSCNT AND RPT REACHING FL310. X IS CLRED TO CLB TO FL350 AND RPT LEAVING FL335. WHEN THE ACFT WERE 4.687 MI APART THE MODE C ALTS WERE X 331 AND Y 315 RESULTING IN 1600 VERT FT OF SEPARATION. AFTER THOROUGH REVIEW IT WAS DETERMINED THAT THE SPEAKER WHERE RADIO XMISSIONS FROM ACFT ARE ROUTED TO WHEN A CTLR LEAVES THE FREQ TO USE A 'LAND-LINE' TO COORD WITH A CTLR AT ANOTHER SECTOR/FACILITY, (WHICH IS CALLED OPTION 'X') WAS IN FACT DISCONNECTED/BROKEN THUS CTLR WOULD NEVER HAVE HEARD X TRANSMISSIONS. NEARLY 3 MINS ELAPSED FROM THE INITIAL ATTEMPT BY X TO CONTACT THE CTLR AND THE RESULTING LOSS OF SEPARATION. SUGGESTION TO AVOID SIMILAR PROBLEMS. FOREIGN AIR CARRIERS, NEW CARRIERS/ CALL SIGNS OR AIR CARRIER/TAXI OPS ENTERING NEW SVC AREAS HAVE CALL SIGNS NOTED IN REMARKS SECTION OF FLT PLAN. SECONDLY PERHAPS AN INDICATOR LIGHT COULD BE INSTALLED TO INDICATE THAT OPTION 'X' SPEAKER/CIRCUIT IS OPERATIONAL.

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.