Narrative:

Phoenix tower advised 'taxi into position and hold runway 8L -- will be in trail of DC10 on departure off runway 8R.' tower then cleared us for immediate takeoff, traffic inside 3 mi final. Shortly after takeoff, I noticed the DC10 converging on our course approximately 3 mi ahead. Tower then asked 'do you have DC10 traffic in sight.' affirmative -- we both (captain and I) had traffic in sight. Tower then advised 'do not exceed 230 KTS in the climb.' I was 'heads inside' programming FMC for climb speed, setting climb power and raising flaps while captain maintained visual contact with the DC10. After completing tasks, I noticed we were slightly left of course on the SID. Looking at the DC10 traffic I also noticed we were 'gaining on him.' while climbing through 5100 ft at 2000 FPM, tower said maintain 5000 ft and contact departure. After switching to departure I advised we were given 5000 ft while climbing through it, now at 5600 ft. Controller then gave heading to 010 degrees but did not tell us to return to 5000 ft but climb 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 degrees. We had the DC10 traffic in sight during our entire departure and climb out. Also, TCASII was silent during entire departure. Supplemental information from acn 382898: after takeoff tower advised that the DC10 was 4 1/2 mi ahead. (Our TCASII showed that the DC10 was about 3 mi ahead.)

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Original NASA ASRS Text

Title: 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.)

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.