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Guest albertomolteni

Radials in SID/STAR file: true or magnetic

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Guest albertomolteni

HelloI have found a similar post about this argument but it didn't solve my doubt completely.I need to convert the COLOCATED expression in SID/STAR files to LATLON. I am using Vincenty's direct method, given point A, the azimuth and length of the geodetic I can find point B.I have also read through Terry Yingling's guide, which reads:Example: FIX DOPIE COLOCATED NRT 256 20This means you are defining a fix called DOPIE which is onthe navaid NRT radial 256 and is 20 miles from NRT.But is that 256 true or magnetic? In theory, if it is a radial, it should be magnetic. But this means that to find the correct location of DOPIE the PMDG FMC should know the magnetic variation for NRT. But this information is not stored in the SID/STAR file, so where does the FMC take it from?Maybe it ignores it completely, in which case radials in SID/STAR files are intended to be already corrected for magnetic variation?Thank you

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You're right. Common geometric expressions use true headings and bearings and SIDSTAR files use magnetic. All navigation data that I am familiar with (not necessarily all inclusive) uses magnetic because that is what pilots fly. In the days before GPS, either the magnetic compass or a fluxgate measurement of earth's magnetic field was the only airborne reference. Land-based equipment, such as VORs and LOCs are configured with respect to local deviation. It makes sense that all charts and procedures follow suit.In your example, 256 is magnetic.FS9 has a default file that provides global declination values, which it uses and add-ons that fly within the FS9 world rely upon. One way to find the local value is to go to slew and hit the space bar. The aircraft will rotate to true north and the heading will reveal the declination. When I am using geometric calculations, I set two fixes at a known true heading and then see what magnetic heading it turns out to be in the FS world... it varies a little from what you'd expect by using other methods, but this method always works.

Dan Downs KCRP

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