Math Skills and GPS Coordinates 

Ok so my math skills leave something to be desired; in flight training ground school I did more math than I had since college and that was long enough ago that it made my head hurt. Now that I’m planning cross country trips it’s giving me opportunities to use those refined skills to calculate trip leg time, ground speed, fuel used, etc via my calculator and e6b manual flight computer. 

However today I found yet another use for math like skills. I was looking at my next cross country (XC) trip and realized that since I picked a reservoir dam and a lake bridge as two of my checkpoints I would have to use gps coordinates to put them in the airplane’s Garmin GTN 750 Gps unit since they wouldn’t be in the aeronautics database. 

Since I’m learning I use the paper chart and plastic protractor to draw out my route and measure my leg headings. I then do all the necessary calculations for time, fuel, etc. However I then use modern electronics and software to double check my work and learn the in and outs of these tools so that when I finish my initial training I can already have a good gasp on them to make advanced training easier. 

So in ForeFlight my dam and bridge look like this. 


At first I thought I had forgotten how to read longitude and latitude……. I just couldn’t figure out how to get 39.89783 on the paper chart since there are only 60 minutes between degrees: correct?

Also I used an iPad app that simulates the airplanes gps unit and it would not accept 39.89783. So I think it over and read a few things and realize that ForeFlight is displaying my waypoint in decimal coordinates instead of degrees, minutes, and seconds. So in order to enter them into the airplane’s gps I have to convert the coordinates to degree, minutes, and seconds. 

E.g.  39.89783 is 39 degrees.  60 x .89783 = 53.8698 so 53 minutes. And 60 x .8698 = 52.188 or 52 seconds. 

So decimal coordinates 39.89783 is N 39 53 52 latitude. 

Or use a website like: https://itouchmap/latlong.html where you can type in the decimal coordinates and it will convert them to degrees, minutes, and seconds and place them on a map so you can visually confirm its the location you want. 

I could then use the Garmin GTN 750 trainer app to make sure the airplane’s gps would accept the coordinates. My converted waypoint is named XC1 and the coordinates are shown in the GTN 750 and displayed on the map. 


So I can use ForeFlight to plan a trip and then convert any non aeronautical database waypoints from decimal coordinates to degrees, minutes, and seconds and enter them into the trainer app to make sure they work. That way on flight day I know I’ll be able to plug them into the aircraft without any issues. 

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