Narrative:

Commuter Y was inbound to phoenix (phx) descending to cross tonto intersection at 11000 ft. Air carrier X was inbound to phx to cross tonto at 12000 ft. Spacing was fine. Air carrier X asked for a shortcut to fly direct tonto. I issued heading 215 degree (later corrected to 220 degree) to intercept the salt river 010 degree radial just outside of tonto. With the shortcut I had to provide vertical separation, so air carrier X was stopped at 13000 ft. Commuter Y was switched to phx approach frequency at 11000 ft. Air carrier X was then reissued the crossing restriction to cross tonto at 11000 ft instead of 12000 ft and aircraft was switched to phx approach frequency. My mind thought I had given air carrier X 12000 but I said 11000 possibly looking at aircraft Y altitude. I cannot remember issuing 11000 ft. I discovered the error when I saw air carrier X descending out of 12000 ft and I called phx approach to question if X had busted his restriction or if approach was using visual separation. Phx responded they were using visual separation now, but air carrier X had come over descending to 11000 ft. My only conclusion is that better awareness on my part could have stopped this error from taking place. Supplemental information from acn 180227: I acknowledged the frequency change and the 'one, one, thousand' level and went to approach. Upon chkin with approach, we were questioned about our altitude, and given a 30 degree right vector to miss the commuter. We immediately got visual contact on the commuter making the heading change unnecessary, approach meanwhile descended commuter Y to a lower altitude and we passed overhead.

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Original NASA ASRS Text

Title: LTSS BTWN ACR AND COMMUTER ACFT. BOTH INBOUND TO PHX. OPAL ERROR.

Narrative: COMMUTER Y WAS INBOUND TO PHOENIX (PHX) DSNDING TO CROSS TONTO INTXN AT 11000 FT. ACR X WAS INBOUND TO PHX TO CROSS TONTO AT 12000 FT. SPACING WAS FINE. ACR X ASKED FOR A SHORTCUT TO FLY DIRECT TONTO. I ISSUED HDG 215 DEG (LATER CORRECTED TO 220 DEG) TO INTERCEPT THE SALT RIVER 010 DEG RADIAL JUST OUTSIDE OF TONTO. WITH THE SHORTCUT I HAD TO PROVIDE VERT SEPARATION, SO ACR X WAS STOPPED AT 13000 FT. COMMUTER Y WAS SWITCHED TO PHX APCH FREQ AT 11000 FT. ACR X WAS THEN REISSUED THE XING RESTRICTION TO CROSS TONTO AT 11000 FT INSTEAD OF 12000 FT AND ACFT WAS SWITCHED TO PHX APCH FREQ. MY MIND THOUGHT I HAD GIVEN ACR X 12000 BUT I SAID 11000 POSSIBLY LOOKING AT ACFT Y ALT. I CANNOT REMEMBER ISSUING 11000 FT. I DISCOVERED THE ERROR WHEN I SAW ACR X DSNDING OUT OF 12000 FT AND I CALLED PHX APCH TO QUESTION IF X HAD BUSTED HIS RESTRICTION OR IF APCH WAS USING VISUAL SEPARATION. PHX RESPONDED THEY WERE USING VISUAL SEPARATION NOW, BUT ACR X HAD COME OVER DSNDING TO 11000 FT. MY ONLY CONCLUSION IS THAT BETTER AWARENESS ON MY PART COULD HAVE STOPPED THIS ERROR FROM TAKING PLACE. SUPPLEMENTAL INFO FROM ACN 180227: I ACKNOWLEDGED THE FREQ CHANGE AND THE 'ONE, ONE, THOUSAND' LEVEL AND WENT TO APCH. UPON CHKIN WITH APCH, WE WERE QUESTIONED ABOUT OUR ALT, AND GIVEN A 30 DEG R VECTOR TO MISS THE COMMUTER. WE IMMEDIATELY GOT VISUAL CONTACT ON THE COMMUTER MAKING THE HDG CHANGE UNNECESSARY, APCH MEANWHILE DSNDED COMMUTER Y TO A LOWER ALT AND WE PASSED OVERHEAD.

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.