Narrative:

Wyldd RNAV 1 departure runway 25R. Climb via 255 degree course lodzy, then via 252 degree course to andyy, then via 184 degree course to idale, then via 100 degree course to hitme, then via 069 degree course to wyldd. Thence: maintain 7000 ft. After takeoff in the navigation mode and at approximately lodzy, departure control issued a clearance to go direct idale and then continue with the wyldd departure. Direct to idale was entered into the flight computer and navigation was engaged. Upon approaching idale, the navigation computer commanded the autoplt to commence a normal leading left turn to intercept the 100 degree outbound course from idale. Las departure control then queried us if we were proceeding to idale. We replied in the affirmative. Las departure control then issued us vectors initially back in the direction of idale and then back eastbound and then finally direct to wyldd and on course. Las departure control then asked us if we had a computer navigation error. They seemed to be concerned with the amount of turn lead the flight computer had commanded. They seemed to expect us to fly direct to idale prior to turning onto the outbound 100 degree course from idale. I explained to them that idale was a 'fly-by' waypoint and that the navigation computer would in fact lead that turn based on speed as versus a 'fly-over' waypoint that does not. Las departure control requested that the crew of flight abc give supervisor a call upon landing at our destination. On terminating flight abcd in memphis, the first officer and myself had a flight debrief with duty officer. After explaining the events that occurred on departure from las, the 3 of us called las departure control and talked with the supervisor. In our telephone conversation with supervisor, he had questions concerning the large turn radius our aircraft made during the first segment of the departure. We explained to him that the turn radius was dictated by the FMC and that we are obligated by our flight operations specifications to follow the computer commanded flight path. He agreed that it was proper to do so but the intercept turn radius seemed larger than other departing aircraft. I have flown this departure many times in the last 2 months and it did not seem to be any different than past departures. This clearance normally does not get any closer than 3 mi from idale during the intercept turn to the 100 degree outbound course from idale. I suspect that it was of greater significance this time due to the timing of the turn reduced spacing from the previously departing aircraft. We discussed the concepts of fly-by and fly-over waypoints and the fact that idale is a fly-by waypoint, which leads to turning short of idale. We assured the supervisor that our safety people would look into this and get back with their safety officer.

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Original NASA ASRS Text

Title: AN A310 CREW, DEPARTING LAS, WERE QUERIED BY ATC ABOUT THE AMOUNT OF WAYPOINT 'TURN LEAD' THAT THE FLT COMPUTER HAD PROGRAMMED INTO THE TURN.

Narrative: WYLDD RNAV 1 DEP RWY 25R. CLB VIA 255 DEG COURSE LODZY, THEN VIA 252 DEG COURSE TO ANDYY, THEN VIA 184 DEG COURSE TO IDALE, THEN VIA 100 DEG COURSE TO HITME, THEN VIA 069 DEG COURSE TO WYLDD. THENCE: MAINTAIN 7000 FT. AFTER TKOF IN THE NAV MODE AND AT APPROX LODZY, DEP CTL ISSUED A CLRNC TO GO DIRECT IDALE AND THEN CONTINUE WITH THE WYLDD DEP. DIRECT TO IDALE WAS ENTERED INTO THE FLT COMPUTER AND NAV WAS ENGAGED. UPON APCHING IDALE, THE NAV COMPUTER COMMANDED THE AUTOPLT TO COMMENCE A NORMAL LEADING L TURN TO INTERCEPT THE 100 DEG OUTBOUND COURSE FROM IDALE. LAS DEP CTL THEN QUERIED US IF WE WERE PROCEEDING TO IDALE. WE REPLIED IN THE AFFIRMATIVE. LAS DEP CTL THEN ISSUED US VECTORS INITIALLY BACK IN THE DIRECTION OF IDALE AND THEN BACK EBOUND AND THEN FINALLY DIRECT TO WYLDD AND ON COURSE. LAS DEP CTL THEN ASKED US IF WE HAD A COMPUTER NAV ERROR. THEY SEEMED TO BE CONCERNED WITH THE AMOUNT OF TURN LEAD THE FLT COMPUTER HAD COMMANDED. THEY SEEMED TO EXPECT US TO FLY DIRECT TO IDALE PRIOR TO TURNING ONTO THE OUTBOUND 100 DEG COURSE FROM IDALE. I EXPLAINED TO THEM THAT IDALE WAS A 'FLY-BY' WAYPOINT AND THAT THE NAV COMPUTER WOULD IN FACT LEAD THAT TURN BASED ON SPD AS VERSUS A 'FLY-OVER' WAYPOINT THAT DOES NOT. LAS DEP CTL REQUESTED THAT THE CREW OF FLT ABC GIVE SUPVR A CALL UPON LNDG AT OUR DEST. ON TERMINATING FLT ABCD IN MEMPHIS, THE FO AND MYSELF HAD A FLT DEBRIEF WITH DUTY OFFICER. AFTER EXPLAINING THE EVENTS THAT OCCURRED ON DEP FROM LAS, THE 3 OF US CALLED LAS DEP CTL AND TALKED WITH THE SUPVR. IN OUR TELEPHONE CONVERSATION WITH SUPVR, HE HAD QUESTIONS CONCERNING THE LARGE TURN RADIUS OUR ACFT MADE DURING THE FIRST SEGMENT OF THE DEP. WE EXPLAINED TO HIM THAT THE TURN RADIUS WAS DICTATED BY THE FMC AND THAT WE ARE OBLIGATED BY OUR FLT OPS SPECS TO FOLLOW THE COMPUTER COMMANDED FLT PATH. HE AGREED THAT IT WAS PROPER TO DO SO BUT THE INTERCEPT TURN RADIUS SEEMED LARGER THAN OTHER DEPARTING ACFT. I HAVE FLOWN THIS DEP MANY TIMES IN THE LAST 2 MONTHS AND IT DID NOT SEEM TO BE ANY DIFFERENT THAN PAST DEPS. THIS CLRNC NORMALLY DOES NOT GET ANY CLOSER THAN 3 MI FROM IDALE DURING THE INTERCEPT TURN TO THE 100 DEG OUTBOUND COURSE FROM IDALE. I SUSPECT THAT IT WAS OF GREATER SIGNIFICANCE THIS TIME DUE TO THE TIMING OF THE TURN REDUCED SPACING FROM THE PREVIOUSLY DEPARTING ACFT. WE DISCUSSED THE CONCEPTS OF FLY-BY AND FLY-OVER WAYPOINTS AND THE FACT THAT IDALE IS A FLY-BY WAYPOINT, WHICH LEADS TO TURNING SHORT OF IDALE. WE ASSURED THE SUPVR THAT OUR SAFETY PEOPLE WOULD LOOK INTO THIS AND GET BACK WITH THEIR SAFETY OFFICER.

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.