General Navigation: Earth, magnetism and the wind triangle
Coordinates and the Earth
Latitude and longitude; the great circle is the shortest distance, the rhumb line has constant track and is easier to fly. One minute of latitude = 1 nautical mile; one minute of longitude = 1 nm × cos(latitude) - the commonest numerical question.
Magnetism
Variation is the angle between true and magnetic north at the position and changes with position and time. Deviation is the error within the aircraft caused by its own magnetic field, read from the deviation card. Conversion: True + Variation = Magnetic, Magnetic + Deviation = Compass ("True Virgins Make Dull Company"). Know turning and dip errors.
Calculations
The 1-in-60 rule: a 1 nm error after 60 nm flown is 1°. Wind triangle: track, heading, drift, ground speed from the wind vector. Time = distance / ground speed; use UTC in flight.
Worked example
You are 3 nm left of track after 60 nm. Required track change is 3° toward track; to regain the intended track, steer about 6° right of track for the same time again, then 3° to hold.
Charts
Mercator: scale constant at the equator, great circle a curve, rhumb line a straight line. Lambert conformal conic: scale constant on the standard parallels, straight lines approximate great circles, used for high-latitude charting. Know how to measure distance and bearing and read the graticule.
Traps
Adding variation when you should subtract; using the wrong sign convention; forgetting that the calculated heading is true and still needs variation and deviation applied.