This puzzle is about magnetic VARIATION. VARIATION is the angle between magnetic north and true north. Flying out of Fort Wayne (FWA) is pretty easy for navigation since our VARIATION is just 6 degrees compared to Juneau, Alaska (PAJN) which is 20 degrees. When VARIATION is zero magnetic north and true north are in a straight line at your position. The VARIATION on your route of flight must be known and your course plotted properly if you are using the aircraft magnetic compass for navigation. Personally, I like GPS navigation since it's easier and more accurate.
True north is located at the Geographic North Pole and is based on the Earth’s axis. The Earth rotates along the axis of the geographic north and south poles where the longitude lines converge.
Magnetic north is located at a different location than true north and is based on Earth’s magnetic field. The Earth’s mantle spins at a different rate than its liquid core, thus magnetic north shifts up to 25 miles (40 km) each year. A magnetic compass always points towards magnetic north.
Of course the above coordinates are wrong so don't go there or you will get wet!
Here are the coordinates to the final cache.
FFL
LS16
FWA
50KY
CID
OTM
CVG
OKK
STL
RFD
AIRNAV is your friend