Narrative:

Cleared to and level at 5000' MSL. Phx approach turned us right to a 170 degree heading for right base for runway 26R. Phx approach called our attention to large transport traffic at 12 O'clock and 11 mi northbound, left base runway 26L. We did not see him at that moment. We advised approach that we had the airport in sight previous to his traffic alert. Continuing southbound we saw the traffic when we were almost through the runway 26R centerline. We told ATC 'traffic in sight.' his response was, 'maintain visual sep.' at that moment my captain banked 45 degrees to the right and descended to 3100' MSL. Approach then said, 'company identification, I show you low with an altitude warning.' my reply was, 'roger, we were avoiding traffic, are you going to clear us for a visual?' my philosophy is, either ATC treats you as if you are IMC or not. No in between. I feel ATC should have given us a turn wbound onto final when we did not report the traffic in sight. Instead, he must have been waiting for us to see him as we were southbound before he would clear us for the visual. In this particular situation, I feel very strongly that the term 'maintain visual sep' is an ambiguous clearance when clearly the timing of the approach was at the point where our flight should have been handled as if it was IMC. Vectors or not? Clearance for visual approach or maintain visual sep? I'm not an expert on ATC guidelines for issuing approach clrncs. In summary, I feel phx approach is accustomed to the frequent VFR WX in their TCA and might expect traffic they point out to be seen. He should have turned us wbound or extended our downwind so as not to have had to head traffic on base legs at matched altitudes. Supplemental information from acn 85013: spacing was being provided between us and air carrier heavy who was approximately 5 mi ahead. We were not cleared a visual or turned and we were bearing directly at the large transport Y at 12 O'clock position who was flying a visual to runway 26L. I elected to bank right and descend to 3100-3300' MSL at 45 degree right bank. I talked to large transport Y captain on ground and he said he was at 4400'. Also talked to TRACON supervisor.

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Original NASA ASRS Text

Title: CLOSE PROX ACR-LGT ACR-LGT ON VECTORS FOR VISUAL APCH TO RWYS 26L 26R PHX.

Narrative: CLRED TO AND LEVEL AT 5000' MSL. PHX APCH TURNED US RIGHT TO A 170 DEG HDG FOR RIGHT BASE FOR RWY 26R. PHX APCH CALLED OUR ATTN TO LGT TFC AT 12 O'CLOCK AND 11 MI NBND, LEFT BASE RWY 26L. WE DID NOT SEE HIM AT THAT MOMENT. WE ADVISED APCH THAT WE HAD THE ARPT IN SIGHT PREVIOUS TO HIS TFC ALERT. CONTINUING SBND WE SAW THE TFC WHEN WE WERE ALMOST THROUGH THE RWY 26R CENTERLINE. WE TOLD ATC 'TFC IN SIGHT.' HIS RESPONSE WAS, 'MAINTAIN VISUAL SEP.' AT THAT MOMENT MY CAPT BANKED 45 DEGS TO THE RIGHT AND DSNDED TO 3100' MSL. APCH THEN SAID, 'COMPANY ID, I SHOW YOU LOW WITH AN ALT WARNING.' MY REPLY WAS, 'ROGER, WE WERE AVOIDING TFC, ARE YOU GOING TO CLR US FOR A VISUAL?' MY PHILOSOPHY IS, EITHER ATC TREATS YOU AS IF YOU ARE IMC OR NOT. NO IN BTWN. I FEEL ATC SHOULD HAVE GIVEN US A TURN WBOUND ONTO FINAL WHEN WE DID NOT RPT THE TFC IN SIGHT. INSTEAD, HE MUST HAVE BEEN WAITING FOR US TO SEE HIM AS WE WERE SBND BEFORE HE WOULD CLR US FOR THE VISUAL. IN THIS PARTICULAR SITUATION, I FEEL VERY STRONGLY THAT THE TERM 'MAINTAIN VISUAL SEP' IS AN AMBIGUOUS CLRNC WHEN CLEARLY THE TIMING OF THE APCH WAS AT THE POINT WHERE OUR FLT SHOULD HAVE BEEN HANDLED AS IF IT WAS IMC. VECTORS OR NOT? CLRNC FOR VISUAL APCH OR MAINTAIN VISUAL SEP? I'M NOT AN EXPERT ON ATC GUIDELINES FOR ISSUING APCH CLRNCS. IN SUMMARY, I FEEL PHX APCH IS ACCUSTOMED TO THE FREQUENT VFR WX IN THEIR TCA AND MIGHT EXPECT TFC THEY POINT OUT TO BE SEEN. HE SHOULD HAVE TURNED US WBOUND OR EXTENDED OUR DOWNWIND SO AS NOT TO HAVE HAD TO HEAD TFC ON BASE LEGS AT MATCHED ALTS. SUPPLEMENTAL INFO FROM ACN 85013: SPACING WAS BEING PROVIDED BTWN US AND ACR HVY WHO WAS APPROX 5 MI AHEAD. WE WERE NOT CLRED A VISUAL OR TURNED AND WE WERE BEARING DIRECTLY AT THE LGT Y AT 12 O'CLOCK POS WHO WAS FLYING A VISUAL TO RWY 26L. I ELECTED TO BANK RIGHT AND DSND TO 3100-3300' MSL AT 45 DEG RIGHT BANK. I TALKED TO LGT Y CAPT ON GND AND HE SAID HE WAS AT 4400'. ALSO TALKED TO TRACON SUPVR.

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.