OPERROR LOSS OF WAKE TURB SEPARATION BTWN A B757 DEPARTING BEHIND IN TRAIL TO A DC10.

Narrative

PHOENIX TWR ADVISED 'TAXI INTO POS AND HOLD RWY 8L -- WILL BE IN TRAIL OF DC10 ON DEP OFF RWY 8R.' TWR THEN CLRED US FOR IMMEDIATE TKOF; TFC INSIDE 3 MI FINAL. SHORTLY AFTER TKOF; I NOTICED THE DC10 CONVERGING ON OUR COURSE APPROX 3 MI AHEAD. TWR THEN ASKED 'DO YOU HAVE DC10 TFC IN SIGHT.' AFFIRMATIVE -- WE BOTH (CAPT AND I) HAD TFC IN SIGHT. TWR THEN ADVISED 'DO NOT EXCEED 230 KTS IN THE CLB.' I WAS 'HEADS INSIDE' PROGRAMMING FMC FOR CLB SPD; SETTING CLB PWR AND RAISING FLAPS WHILE CAPT MAINTAINED VISUAL CONTACT WITH THE DC10. AFTER COMPLETING TASKS; I NOTICED WE WERE SLIGHTLY L OF COURSE ON THE SID. LOOKING AT THE DC10 TFC I ALSO NOTICED WE WERE 'GAINING ON HIM.' WHILE CLBING THROUGH 5100 FT AT 2000 FPM; TWR SAID MAINTAIN 5000 FT AND CONTACT DEP. AFTER SWITCHING TO DEP I ADVISED WE WERE GIVEN 5000 FT WHILE CLBING THROUGH IT; NOW AT 5600 FT. CTLR THEN GAVE HDG TO 010 DEGS BUT DID NOT TELL US TO RETURN TO 5000 FT BUT CLB TO 13000 FT. ON THE NEW HEADING WE DIVERGED APART AND WENT NORMALLY ON OUR SEPARATE WAYS. I WOULD ESTIMATE PASSING 2 MI FROM THE DC10 WHILE IN TRAIL AND DURING OUR TURN TO 010 DEGS. WE HAD THE DC10 TFC IN SIGHT DURING OUR ENTIRE DEP AND CLBOUT. ALSO; TCASII WAS SILENT DURING ENTIRE DEP. SUPPLEMENTAL INFO FROM ACN 382898: AFTER TKOF TWR ADVISED THAT THE DC10 WAS 4 1/2 MI AHEAD. (OUR TCASII SHOWED THAT THE DC10 WAS ABOUT 3 MI AHEAD.)