Narrative:

Due to prevailing winds, takeoff was made from runway 20 at this uncontrolled airport. The rco was used to obtain IFR clearance through raleigh radio prior to takeoff. Clearance was 'direct aqe, direct ilm, flight planned route, climb and maintain 3000 ft.' the FMS was programmed to match the clearance due to geographic position of runway 20, aqe, and ilm, the required course change at the NDB was almost 180 degrees. Since no IFR departure procedure is published for this airport, we briefed a left turn to aqe, considering the l-hand traffic pattern. At 400 ft AGL we initiated a left turn using the flight director (25 degrees of bank) and kept airspeed restr to 200 kcas to reduce the radius of turn (later calculated to be approximately 1.25 NM). PNF selected 'direct aqe' on FMS and PF selected LNAV. At this time, initial contact was established with center. Once the turn was complete, approximately course to aqe was 350 degrees. About 2-3 NM prior to aqe, turn anticipation logic of FMS commanded left turn to join track from aqe to ilm. During turn, center asked if we were proceeding direct aqe. We responded that we had been, but were now starting turn towards ilm. Controller then stated 'it doesn't look like you went over aqe' and then issued radar vector of 270 degrees. This required a turn reversal to the right, as current aircraft heading was passing 240 degrees. We offered explanation that what controller saw on scope was turn anticipation by the FMS. We were subsequently cleared 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 clear that 'the FAA expects pilots to lead turns and take other actions they consider necessary during course changes to adhere as closely as possible to the airways or route being flown.' from our perspective as pilots, the best tool available to comply with this requirement is the FMS. In the absence of a 'fly-over' instruction in a published procedure or the ATC clearance. We do not understand the controller's expectation that the ground track would pass directly over the NDB prior to initiating the turn to the next leg. This expectation is especially concerning if terrain clearance and/or aircraft separation depends upon it. In addition, it appears that some controllers still do not understand the concept of turn anticipation. This proved to be a critical issue last yr during implementation of new RNAV departures in las vegas. The amount of lead computed by the FMS varies, depending on the FMS make/model as well as aircraft altitude/ground speed, amount of course change, and wind drift. This results in varying ground 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 procedures.

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Original NASA ASRS Text

Title: 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.

Narrative: 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.

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.