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TheDanger

Lat/Lon problem at EGCC POL VOR

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HiI'm having a problem with regards to EGCC LIS1Z for 5R DmeIntc53.356944-2.262222000at0551.2AutoI can calculate the lat/lon of the point on the 55 radial, 1.2 nm from the MCT VOR accurately. (INTC)Intc53.743889-2.103333000at090188AutoDmeIntc53.743889-2.103333020000above018824AutoLooking at waypoint 3 above I calculate the lat/lon of the point on the 188 radial, 24nm from the POL VOR.(calculating from radians to deg/min gives lat of 53 44.633340 and lon of -2 6.199980 for the POL VOR, entering these into the online calculator gives me the position as show below)Question is why does the 188 from the POL VOR appear to be more to the left than the intercept line on the flightplan?Is this something to do with your navdata?Many thanksGrahamhttp://forums.avsim.net/user_files/188190.jpghttp://forums.avsim.net/user_files/188191.jpg

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After a bit more investigation I have flew the cessna 172 on radial 188 at dme from POL VOR of 24 and it more or less is correct with the white flight plan line corner.That means that the formula I am using must be incorrect yet I have coded the formula and also used several online calculators and they all point to the same result as where my aircraft is on the above picture.Whats wrong here? Any ideas?Thanks

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Hi,Wish I could edit these posts!Been looking at some older navdata files including user ones and I've noticed that you have intercept heading of 90 deg yet most other files have around 150 deg.Is this correct do you think?thanksGraham

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Hi Graham,>Wish I could edit these posts!You can. Once you post your message a new window pops up showing what you posted. You can then edit your post by clicking the word EDIT from the menu under your post. That is what I did to include these three sentences.>Been looking at some older navdata files including user ones>and I've noticed that you have intercept heading of 90 deg yet>most other files have around 150 deg.Let's see if I can answer this and make sense of it. Have a look at the LIS1S and LIS1Z charts. The LIS1S is for 05L and shows a track of 150 degrees to intercept the 188 radial. The LIS1Z for 05R does not do this and just uses one big turn to intercept the 188 radial. That I think explains the use of the 150 degrees you mention. Perhaps those that used the 150 degrees for LIS1Z either did not notice this or used it anyhow for whatever reason.As for the 90 degree course that is just a number I picked to get the plane heading toward the 188 radial. I am limited to using ARINC track descriptions when designing procedures which in this case is a CI, a course to intercept. To make a CI leg I have to supply a course heading to the intercepted radial. This intercept course is just my guess at what might work best. Some times I pick an angle that looks about right and other times I pick a course that provides an intercept angle of 90 degrees to the radial. In this case I used a course of 90 degrees. If I had used the 90 intercept angle method then it would have been a course of 98 degrees instead. I could have also just used the heading of 55 degrees from takeoff but by doing so I have no control over when the turn is initiated. The FMC would simply calculate when to turn so it would intercept the 188 radial at the end of the turn. That results in a sharp turn that would have been initiated further out than the 1.2 miles the procedure wants you to start the turn. By using the 90 degree course that forces the FMC to immediately turn the plane so I can dictate when the plane turns, in this case at 1.2 miles. This particular SID illustrates one of the problems of converting a drawing into standard ARINC codes. Sometimes the translation is just not exact.Clear as mud?RegardsTerry

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Hi Terry,Yes I understand what you outline above.I've sorted the problem now, well my interpretation of the problem anyhow. Instead of using LNAV at 450ft agl on takeoff I used HDG SEL, track 55deg for 1.2nm then whizz around to the right at 188deg and then LNAV again when on the outbound radial.Works fine now.Still have the problem in my first post but I suppose its not related to your data anyhow. I still cant figure out why the aircraft is not placed on the correct position (188deg radial at 24nm from POL VOR).I've solved that by reading the lat/lon values from FSBuild flight plan and copying them into my runway transition array and it works perfect now.Thanks for your help TerryBest regardsGraham

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