A G4 ON IFR DEP FROM AN UNCTLED ARPT. BECAUSE THE FIRST AIRWAY FIX WAS IN CLOSE PROX TO THE DEP ARPT; THE FMS TURN ANTICIPATION LOGIC DID NOT MARK ON TOP OF FIX. ATC QUESTIONED PLTS.

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DUE TO PREVAILING WINDS; TKOF WAS MADE FROM RWY 20 AT THIS UNCTLED ARPT. THE RCO WAS USED TO OBTAIN IFR CLRNC THROUGH RALEIGH RADIO PRIOR TO TKOF. CLRNC WAS 'DIRECT AQE; DIRECT ILM; FLT PLANNED RTE; CLB AND MAINTAIN 3000 FT.' THE FMS WAS PROGRAMMED TO MATCH THE CLRNC DUE TO GEOGRAPHIC POS OF RWY 20; AQE; AND ILM; THE REQUIRED COURSE CHANGE AT THE NDB WAS ALMOST 180 DEGS. SINCE NO IFR DEP PROC IS PUBLISHED FOR THIS ARPT; WE BRIEFED A L TURN TO AQE; CONSIDERING THE L-HAND TFC PATTERN. AT 400 FT AGL WE INITIATED A L TURN USING THE FLT DIRECTOR (25 DEGS OF BANK) AND KEPT AIRSPD RESTR TO 200 KCAS TO REDUCE THE RADIUS OF TURN (LATER CALCULATED TO BE APPROX 1.25 NM). PNF SELECTED 'DIRECT AQE' ON FMS AND PF SELECTED LNAV. AT THIS TIME; INITIAL CONTACT WAS ESTABLISHED WITH CTR. ONCE THE TURN WAS COMPLETE; APPROX COURSE TO AQE WAS 350 DEGS. ABOUT 2-3 NM PRIOR TO AQE; TURN ANTICIPATION LOGIC OF FMS COMMANDED L TURN TO JOIN TRACK FROM AQE TO ILM. DURING TURN; CTR ASKED IF WE WERE PROCEEDING DIRECT AQE. WE RESPONDED THAT WE HAD BEEN; BUT WERE NOW STARTING TURN TOWARDS ILM. CTLR THEN STATED 'IT DOESN'T LOOK LIKE YOU WENT OVER AQE' AND THEN ISSUED RADAR VECTOR OF 270 DEGS. THIS REQUIRED A TURN REVERSAL TO THE R; AS CURRENT ACFT HDG WAS PASSING 240 DEGS. WE OFFERED EXPLANATION THAT WHAT CTLR SAW ON SCOPE WAS TURN ANTICIPATION BY THE FMS. WE WERE SUBSEQUENTLY CLRED DIRECT ILM AND THERE WAS NO FURTHER DISCUSSION. WE FOUND THIS EVENT TROUBLING ON SEVERAL LEVELS. PARAGRAPH 5-3-5 OF THE AIM IS VERY CLR THAT 'THE FAA EXPECTS PLTS TO LEAD TURNS AND TAKE OTHER ACTIONS THEY CONSIDER NECESSARY DURING COURSE CHANGES TO ADHERE AS CLOSELY AS POSSIBLE TO THE AIRWAYS OR RTE BEING FLOWN.' FROM OUR PERSPECTIVE AS PLTS; THE BEST TOOL AVAILABLE TO COMPLY WITH THIS REQUIREMENT IS THE FMS. IN THE ABSENCE OF A 'FLY-OVER' INSTRUCTION IN A PUBLISHED PROC OR THE ATC CLRNC. WE DO NOT UNDERSTAND THE CTLR'S EXPECTATION THAT THE GND TRACK WOULD PASS DIRECTLY OVER THE NDB PRIOR TO INITIATING THE TURN TO THE NEXT LEG. THIS EXPECTATION IS ESPECIALLY CONCERNING IF TERRAIN CLRNC AND/OR ACFT SEPARATION DEPENDS UPON IT. IN ADDITION; IT APPEARS THAT SOME CTLRS STILL DO NOT UNDERSTAND THE CONCEPT OF TURN ANTICIPATION. THIS PROVED TO BE A CRITICAL ISSUE LAST YR DURING IMPLEMENTATION OF NEW RNAV DEPS IN LAS VEGAS. THE AMOUNT OF LEAD COMPUTED BY THE FMS VARIES; DEPENDING ON THE FMS MAKE/MODEL AS WELL AS ACFT ALT/GND SPD; AMOUNT OF COURSE CHANGE; AND WIND DRIFT. THIS RESULTS IN VARYING GND TRACKS THAT ARE NOT ALWAYS PREDICTABLE OR REPEATABLE. THE SOLUTION TO THIS ISSUE IS THE USE OF RF (RADIUS-TO-FIX) LEGS IN THE FMS. HOWEVER; THIS LEG TYPE IS NOT PRESENTLY USED IN STANDARD IFR PROCS.