TWR IMPROPERLY APPLIED VISUAL SEPARATION ACR X HAD NMAC LTSS FROM ACR Y. EVASIVE ACTION TAKEN. SYS ERROR.

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THE EVENT TOOK PLACE IN PHX ON JAN/XX/92. WE WERE GIVEN A TKOF CLRNC ON RWY 8L. PHX N TWR SAID THAT THERE WAS TFC DEPARTING RWY 8R AND RPT IT IN SIGHT. WE RPTED THE TFC IN SIGHT SHORTLY AFTER TKOF. ATC TOLD US TO MAINTAIN VISUAL SEPARATION FROM THAT TFC. THE FIRST RESTRICTION IN THE PASO 6 DEP WAS TO CROSS THE 4 DME OF SALT RIVER AT OR BELOW 3000. OUR CLRNC WAS TO MAINTAIN 8000. THE NORMAL PROC IS TO CLB TO 1000 FT AGL AT V2 PLUS 10 KTS THEN CLEAN UP AND CLB OUT AT 0 FLAP MANEUVER TO 3000 FT AGL. ON THIS DAY; WE (ACR X) HAD ALL THE SEATS FULL; THE TKOF WT WAS 292000 AND OUR 0 FLAP MANEUVER WAS 230 KTS. ATC TOLD US OUR SPD WAS 30 KTS FASTER THAN ACR Y. (WE DIDN'T KNOW THE SIGNIFICANCE OF WHAT HE WAS TRYING TO TELL US AT THE TIME ALTHOUGH NOW WITH 20/20 HIND SIGHT I KNOW HE WANTED US TO FOLLOW ACR Y.) WE WERE JUST TOLD TO MAINTAIN VISUAL. (WE SHOULD HAVE ASKED THEN AND THERE WHAT IS ACR Y GOING TO DO. THE CONTRIBUTING FACTOR HERE IS WE DID NOT HEAR HIS CLRNC ON THE S TWR FREQ.) WE DIDN'T KNOW THAT ACR Y WAS NOT ADVISED OF OUR PARALLEL DEP WHEN HE WAS CLRED FOR TKOF ON RWY 8R. THE PASO 6 DEP; THE ONE WE WERE CLRED ON; IS AN 080 HDG TO 1 DME. WE DIDN'T KNOW WHAT ACR Y WAS FLYING. AT APPROX 2.6 DME POINT; ACR Y; OF WHICH I HAVE VISUALLY AT ABOUT 2-3 MI AT MY 1 O'CLOCK POS; MAKES A SHARP L TURN (WHICH I LATER CONCLUDED WAS HIS ON COURSE HDG OF 330 FROM LOOKING AT THE OTHER SIDS). THAT IS GOING FROM MY 1 O'CLOCK AT 2-3 MI INTO A 100 DEG HDG CHANGE ACROSS MY FLT PATH. OUR HORIZ SEPARATION CLOSED RAPIDLY WITH HIM UNAWARE OF OUR PRESENCE HE WENT AT A MAX RATE TURN. TO MAINTAIN MY PRESENT HORIZ SEPARATION AND VISUAL CONTACT I TURNED WITH HIM; THINKING HE WAS MAKING A MINOR COURSE CORRECTION. THE SMALLER AND LIGHTER ACFT WAS QUICKLY OUT TURNING US. AT THIS TIME WE WERE FORCED TO TAKE EVASIVE ACTION; I.E.; A DSCNT TO INCREASE OUR VERT SEPARATION AND AVOID ACR Y. NO UNUSUAL ATTITUDES OR G FORCES WERE REQUIRED. THE LACK OF COM OF WHAT WAS GOING TO HAPPEN. I KNOW NOW WHAT THE CTLR WAS INTENDING BUT NOT AT THE TIME. I THINK WE SHOULD HAVE BEEN GIVEN A VERT SEPARATION AT LEAST IN THIS INSTANCE OR TOLD HE IS TURNING L TO A 330 HDG YOU GO TO THE R OF HIM. IT WAS WHAT I CALL AN IMPLIED CLRNC. SUPPLEMENTAL INFO FROM ACN 198033: THE TFC OFF RWY 8R WAS ON A DIFFERENT TWR RADIO FREQ SO WE HAD NOT HEARD HIS DEP INSTRUCTIONS NOR WERE WE AWARE OF WHICH SID HE WOULD BE FLYING. TWR HANDED US OFF TO DEP CTL WITHOUT TELLING US WHICH WAY (L OR R) OR WHEN ACR Y AHEAD WOULD BE TURNING TO ON COURSE. ACR Y WAS NEVER ADVISED OF OUR ALMOST SIMULTANEOUS DEP ON 8L. OUR SID (PAYSO 6) REQUIRED 080 DEG HDG UNTIL 1 DME (INBOUND) TO SRP VOR. AT APPROX 2.6 DME (INBOUND) ACR Y BEGAN A HARD AND TIGHT L TURN DIRECTLY INTO OUR FLT PATH. OUR CLOSURE RATE WITH ACR Y GREW VERY RAPIDLY. WE STARTED A L TURN TO AVOID ACR Y. WE WERE UNABLE TO OUT TURN HIM TO THE L AND WE WERE FORCED TO MAKE A RAPID DSCNT TO LET HIM PASS OVERHEAD. SUPPLEMENTAL INFO FROM ACN 198152: ON TKOF FROM PHOENIX RWY 8R ON DRAKE DEP WE WERE TURNED L IN FRONT OF DEPARTING TFC ON 8L. WE SIMPLY GOT A HDG CHANGE INSTRUCTION -- NOT 'WATCH FOR TFC OFF OF 8L' LIKE THEY USUALLY DO. I DID NOT CLR L REAL GOOD AND WHEN I HEARD PHX DEP TELL AN ACFT TO 'GO BEHIND HIM'; I LOOKED OUT MY L WINDOW AND THERE WAS ACR X COMING RIGHT AT ME IN A L TURN (LIKE HE WAS TRYING TO AVOID ME) AND GOING RIGHT UNDER MY ACFT -- CLRED BY 200-300 FT BELOW. IT SCARED ME IT WAS SO CLOSE. I TOLD PHX DEP IT WAS A 'NEAR MIDAIR' AND CONTINUED ON WITH FLT TO SEATTLE. I'M SURPRISED IT DIDN'T SHOW UP TO THE CTLR ON RADAR WHAT WAS HAPPENING; WHETHER HE WAS DISTRACTED OR WHAT. I THINK BY TELLING US BOTH WHAT WAS PLANNED WOULD HAVE AVOIDED SURPRISE BY BOTH ACFT AND WE WOULDN'T HAVE COME SO CLOSE.