MODIFICATION OF THE IDALE RNAV 1 DEP AT LAS; NV; WITH A VECTOR FOLLOWED BY A PLT REQUESTED DIRECT SHEAD INTXN WITH PLT PROVIDED TERRAIN CLRNC ENDS WITH AN ALT OVERSHOOT CAUSING A TFC CONFLICT.

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ALTDEV. DEPARTED LAS FROM RWY 19L ON IDALE RNAV DEP. CHKED IN WITH DEP AND RECEIVED A 200 DEG VECTOR WITH CLB TO 11000 FT. PASSING 7000 FT REQUESTED A TURN TO THE W MAINTAINING OUR OWN TERRAIN CLRNC TO EXPEDITE THE DEP (GOOD WX/VISIBILITY; LIGHT TFC WITH TERRAIN EASILY VISIBLE). REQUEST APPROVED BY LAS DEP VIA DIRECT SHEAD INTXN; MAINTAIN 11000 FT. ENTERED SHEAD INTO THE FMC; BEGAN A TURN TO THE W; AND AS LUCK WOULD HAVE IT THE ONLY PEAK ON THE RIDGE LINE WAS ALONG OUR FLT PATH. THE CAPT FELT WE WOULD PASS TOO CLOSE TO THAT RIDGE AND TURNED 30 DEGS R/N OF THE DIRECT COURSE FOR A MOMENTARY DEV TO ENSURE TERRAIN CLRNC. NO CALL WAS MADE TO THE CTLR DUE TO THE MOMENTARY NATURE OF THE DEV AND WE HAD NOT ESTABLISHED THE TRACK TO SHEAD. LAS CTLR BECAME CONCERNED AND ISSUED US DIRECT SHEAD AGAIN AS WE WERE IN OUR TURN DIRECT SHEAD. THIS WAS FOLLOWED BY A DIRECTED HDG OF 240 DEGS; THAT WE COMPLIED WITH. LAS THEN GAVE US A TFC CALL OF L 11 AND 5 MI 200-3000 FT ABOVE OUR PRESENT CLBING ALT. WE BOTH BEGAN SEARCHING FOR THE TFC AND CALLED 'IN SIGHT.' THIS OCCURRED AS WE APCHED OUR LEVELOFF ALT OF 11000 FT DIVERTING OUR ATTN AWAY FROM THE LEVELOFF. THE CAPT WAS HAND FLYING THE DEP SO NO AUTO ALT CAPTURE WAS AVAILABLE. AS WE PASSED 11200 FT; I CALLED OUT OUR DEV AND AN IMMEDIATE CORRECTION WAS PERFORMED. WE TOPPED OUT AT 11450 FT BEFORE DSNDING BACK TO 11000 FT. THE PREVIOUSLY RPTED TFC PASSED 3 NM IN FRONT OF US AT 12000 FT; WITH A TCASII TA ALERT. THE CTLR ASKED US TO CONFIRM OUR ALT; WHICH WAS NOW 11000 FT. WE RECEIVED A HDOF TO ZLA WITH NO FURTHER COMMENTS. LESSONS: 1) MAINTAIN SITUATIONAL AWARENESS BY ALL MEANS AVAILABLE. 2) USE OF AUTOPLT CAN AID WHEN DISTR. 3) INFORM THE CTLR OF ALL DEVS. 4) IF THERE IS AN OBSTACLE ANYWHERE BTWN WHERE YOU ARE AND WHERE YOU WANT TO GO; IT WILL BE ALONG THE COURSE YOU ARE GIVEN. SUPPLEMENTAL INFO FROM ACN 562986: MAKE ALT AWARENESS AND CTL A TOP PRIORITY.