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gmohr

Nav Log vs VOR Radial ... error? Help!

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Hi all,Quick scenario, create a flight plan IFR using High Alt from Key West Int (KEYW) to Space Coast Reg (KITX). Find Route will give you something like this:KEYW EYW (VOR) -D-> CARNU (waypoint) J79etc...The airway from EYW to CARNU is J79. The Flight planner will give you a heading of 042 for this leg (42 miles). However, on the actual chart (http://skyvector.com) you can see that this airway is on the 037 radial outbound from EYW. A database error you say? Well maybe, but if you actually fly the 042 radial outbound from EYW, you will quickly deviate south of your course as shown on the GPS.So here's my (somewhat obtuse) question... Why does the Nav Log generated by the flight planner give an inaccurate heading on this leg? Has anyone else stumbled on this problem? Am I simply simple?Help! and thanks,George

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George,This question comes up occasionally. It has to do with changes in magnetic north models over time.Airnav.com shows the EYW VOR has a magnetic variation of 1E, using data from 1965.The published variation for KEYW airport is 4W, using year 2000 data. The FSX flight planner and GPS also use magvar data from 2000.If you fly the J79 airway on a true course of 038, you will be flying the 037 radial from the EYW VOR (38 - 1 = 37), but your compass bearing will be 042 (38 + 4 = 42). This assumes the absence of a crosswind, of course.This situation is quite common in the USA. Many VOR navaids are defined using old data. FAA policy calls for realignment of the VOR when published and current magvar data are off by 6 degrees or more.Looks like they need to put EYW on the list.Todd

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Hi Todd, thanks for the reply.Ok, so I'm clearly not understanding my VOR navigation correctly. So then, if I wanted to find the radial to fly outbound, I have to take the heading given to me in the nav log, and apply the local variation... ... no actually what you are saying is I should look at the d*mn enroute chart and see what the radial is for J79 rather than calculating it from the nav log. Gotcha hehe.My R/L PPL is a glider rating so my VOR is really rusty lol. Thanks again!

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