But again, at sufficient distance this is negligable.- As said above, not all Localisers are on the runway centerline.- The value of 'a' may not always be 1.7 degrees. via a line from current aircraft position 90 degrees on centerline.''y': DME'z': the distance to the centerline, on the current aircraft heading.'w': the DME value at intercept point, at current aircraft heading.So:- 'x' = 'b' / 127 * 'y' * sin('a')- 'z' = 'x' / cos('c')- 'w' = Sqrt ( 'y'(2) - 'x'(2) ) - Sqrt ( 'z'(2) - 'x'(2) )So given position, airspeed and desired bankangle, it just lacks a formula at which 'x' you should initiate the turn to intercept the centerline with nearly 0 'c' because that's what you want, right ?I would make this formula adaptive anyway (based on change speed of 'x'), since you also have to take changing winddirection (relative to the aircraft heading) into account.A few sidenotes:Although the formula's above are correct, there are a few shortcuts that will influence it.- DME also includes an altitude component but at sufficient distance from the runway and normal approach altitude this is negligable.- On most runways I've seen in FS, the DME (if any) isn't located at the Localiser (on or beyond end-of-runway) but at Glideslope position (start-of-runway). part 0 - 127 here)'c': the current angle of intercept between aircraft heading and LOC centerline heading so 0 means aircraft is on centerline heading (on or parallel to centerline (for simplicity, I assume between 0 and 90 degrees).'x': the shortest distance between the aircraft and the LOC centerline i.e. ![]() (I just measured that with my XML distance calculator gauge on several runways in FSX.'b: the value of the FS LOC variable (for simplicity: I only use the pos. where the LOC-value changes from 0 to 127 (or 0 -127). Hi Dai,Here' some other formula's:A few definitions:'a': half the beam-width of the Localizer i.e. Maybe this depends on runway length IRL ?In short: making the perfect Localiser interceptor that works on any ILS, on any airport and for any aircraft isn't as simple as it looks :( In fact, I think one could make a much more accurate (without the shortcuts above) "runway centerline intercept function" based on GPS data for position/altitude of the touchdown point, and not based on the FS Localizer.Succes, Rob ![]() ![]()
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