B737-300 CAPTAIN REPORTS DEPARTURE CONTROL IS DELETING ALTITUDE AND SPEED RESTRICTIONS ON RNAV SIDS ASSIGNED BY CLEARANCE DELIVERY. FEELS THIS IMPOSES UNDESIRABLE WORKLOAD ON FLIGHT CREWS TO UNDO THE ALREADY PROGRAMMED RESTRICTIONS.

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CLRNC HAD LEETZ1 DEP. SLC DEPS ARE VERY WORKLOAD INTENSIVE AS MOST FIXES CONTAIN BOTH AN ALT AND AIRSPD CONSTRAINT. MUCH TIME IS SPENT IN THE PREFLT COCKPIT SETUP VERIFYING THE FIXES; SPDS AND ALTS IN THE FMC. ONE SUCH RESTR ADDED TO THE ATC (PDC) CLRNC IS 'MAINTAIN 230 KTS;' WHICH IS PROGRAMMED INTO THE CLB PAGE OF VNAV. UPON DEP; USING BOTH LNAV AND VNAV AS REQUIRED FOR THE DEP (JUST LIKE DFW; ATL; ETC) DEP CTL GIVES US THE FOLLOWING COMMAND: 'FLY HDG 330 DEGS; DELETE THE SPD RESTRS; CLB TO FL230 AND EXPECT DIRECT CHITO.' THIS COMMAND/CLRNC; WHILE SEEMINGLY INNOCUOUS; PRESENTS US WITH A TREMENDOUS WORKLOAD REPROGRAMMING THE FMC AT A VERY LOW LEVEL; HIGH WORKLOAD; CRITICAL PHASE OF FLT. YES; LEVEL CHANGE AND HDG SELECT CAN BE USED IF YOU ARE EXPECTING THIS AND ON-TOP OF THE SIT; BUT IT STILL REPRESENTS A HUGE WORKLOAD AT A CRITICAL PHASE OF FLT. THE CREWS' EXPECTATION ON ANY OF THESE NEW SID PROCS IS TO FLY THE MAJORITY OF THE SID IN THE PLANNED LNAV/VNAV PROFILE. TAKING THE FLT OFF OF BOTH THE LNAV AND VNAV PROFILE AT 1000 FT AND ISSUING A NEW CLRNC IS TOO MUCH WORKLOAD AND TOO DISTRACTING AT A CRITICAL PHASE OF FLT. IT ALSO OPENS UP THE POSSIBILITY OF NEW PROGRAMMING ERRORS BEING MADE IN A HURRY DURING A HIGH WORKLOAD PHASE OF FLT. IF ATC NEVER INTENDS FOR THE CREWS TO FLY THE VERT OR LATERAL PROFILE; THEN THEY SHOULD NOT BE ISSUING THE SID. PERHAPS A RADAR VECTOR SID INSTEAD. THIS ALSO OCCURRED TO US 2 DAYS EARLIER USING THE SBOUND SID. SAME THING -- TOOK US OFF OF THE VERT AND LATERAL PROFILE AT 1000 FT WITH FIRST CONTACT WITH DEP CTL. APPARENTLY THIS HAPPENS FREQUENTLY WHEN ACFT INBOUND ON THE VARYING STARS ARE NOT IN CONFLICT WITH EARLY CLBOUTS ON THE DEP.