Narrative:

We were cleared for the mountain 2 departure with radar vectors to J-90. We departed runway 34L a sea tac at xa:55 local time 9/90. The departure calls for being at or above 4000' at 8 DME of the sea VOR then turn right to a heading of 070 degree. We were operating aircraft which has the modification. Company procedures require a 'quiet EPR departure' over all populated areas. To accomplish this departure procedure the thrust is reduced to, in this case, 1.46 EPR. My copilot was making the takeoff and he called for quiet EPR upon cleaning up the aircraft. While retarding the throttles from 2/17 to 1.46 I checked to determine if we were going to make the crossing restriction and it appeared we would. While I was in the process of a gradual reduction to 1.46 EPR the copilot initiated a right turn toward 070 degree. I did not check at this point to see the DME about 40 degree into this 92 degree turn. Departure control called to verify our assigned SID. I notified him, the mountain two. He then said we turned too soon and gave us a turn to 340 degree. Immediately upon reaching 340 degree he turned us to 110 degree heading intercept J-90. When he asked my DME I told him 8 DME. He said his radar showed 5 mi. I later determined that the copilot lead the turn rather than turn at 8 DME. He may also have thought he was supposed to turn at 4000'. However, by the time ATC questioned our DME I was reading 8 DME so apparently the turn was started too soon. Had I not been setting the power I would have caught the error.

Google
 

Original NASA ASRS Text

Title: ACR FREIGHT OPERATION FLYING SID TURNS TOO SOON. HEADING DEVIATION.

Narrative: WE WERE CLRED FOR THE MOUNTAIN 2 DEP WITH RADAR VECTORS TO J-90. WE DEPARTED RWY 34L A SEA TAC AT XA:55 LCL TIME 9/90. THE DEP CALLS FOR BEING AT OR ABOVE 4000' AT 8 DME OF THE SEA VOR THEN TURN R TO A HDG OF 070 DEG. WE WERE OPERATING ACFT WHICH HAS THE MODIFICATION. COMPANY PROCS REQUIRE A 'QUIET EPR DEP' OVER ALL POPULATED AREAS. TO ACCOMPLISH THIS DEP PROC THE THRUST IS REDUCED TO, IN THIS CASE, 1.46 EPR. MY COPLT WAS MAKING THE TKOF AND HE CALLED FOR QUIET EPR UPON CLEANING UP THE ACFT. WHILE RETARDING THE THROTTLES FROM 2/17 TO 1.46 I CHKED TO DETERMINE IF WE WERE GOING TO MAKE THE XING RESTRICTION AND IT APPEARED WE WOULD. WHILE I WAS IN THE PROCESS OF A GRADUAL REDUCTION TO 1.46 EPR THE COPLT INITIATED A R TURN TOWARD 070 DEG. I DID NOT CHK AT THIS POINT TO SEE THE DME ABOUT 40 DEG INTO THIS 92 DEG TURN. DEP CTL CALLED TO VERIFY OUR ASSIGNED SID. I NOTIFIED HIM, THE MOUNTAIN TWO. HE THEN SAID WE TURNED TOO SOON AND GAVE US A TURN TO 340 DEG. IMMEDIATELY UPON REACHING 340 DEG HE TURNED US TO 110 DEG HDG INTERCEPT J-90. WHEN HE ASKED MY DME I TOLD HIM 8 DME. HE SAID HIS RADAR SHOWED 5 MI. I LATER DETERMINED THAT THE COPLT LEAD THE TURN RATHER THAN TURN AT 8 DME. HE MAY ALSO HAVE THOUGHT HE WAS SUPPOSED TO TURN AT 4000'. HOWEVER, BY THE TIME ATC QUESTIONED OUR DME I WAS READING 8 DME SO APPARENTLY THE TURN WAS STARTED TOO SOON. HAD I NOT BEEN SETTING THE PWR I WOULD HAVE CAUGHT THE ERROR.

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.