By now, we've finished the first part of the quite extensive course on Navigation.
A peculiar thing I've learned is that an aircraft flying has not one direction but three. It has not one speed but about 4 or 5.
Course or Track
An aircraft flies a certain course, for example 090, which means 90° or east. There are 359 possible courses (0° - 359°).
Life would be simple if the compass in the aircraft points to where the aircraft is going. But it's not.
True and magnetic course
If you want to go somewhere, typically you use a map first. You find out what course you need to fly in to go from point A to point B.
This is called the True Course.
On a map, 0° North is usually at the top. This is the True North. In real life, North is somewhere near the north pole. This is the Magnetic North.
The Magnetic North is always moving and usually not in the same place as the True North.
So your True Course is relative to the True North. But your Magnetic Course will be slightly different, because it is relative to the Magnetic North.
It's possible to know where the Magnetic North is and how much it differs from the True North: the difference is called the Variation (V):
Variation = angle between the True North and the Magnetic north
For example: if the Variation is +10° (or 10° East), and you are facing the True North, you will find the Magnetic North 10 degrees to your right.
The Variation depends on your location on earth. Usually, the Variation is mentioned on the map you are using.
If you want to fly a heading of 90° on the map, but the Magnetic North is 10° to your right. Your compass will only show 80°. So if you want to fly a True Course of 90° you must fly a heading of 80° relative to the Magnetic North.
Even more fun: the Magnetic North is always moving, so the Variation on a certain location changes over time.
So that's two courses:
- True Course (based on the Map)
- Magnetic Course (based on the Magnetic North)
You'd think the compass would show the Magnetic Course. But because of the surroundings the compass deviates a bit from that. The difference is called the deviation (d).
It gets even more confusing: the deviation depends on the direction you are facing!
A compass always comes with a card that shows the deviation based on the course:
It's important to know the "To Fly" course is referring to the Magnetic Course and not the True Course.
To know which direction you need to fly you need to do the following:
- Find the True Course using a map
- Apply the appropriate Variation to obtain the Magnetic Course
- Apply the appropriate Deviation to obtain the Compass Course
The order of the steps is important.
True Course + Variation = Magnetic Course + Deviation = Compass Course
Or in short:
T + V = M + d = C
Some people use the following - inappropriate but easy to remember - sentence to remember the order:
True Virgins Make Dull Companions
At any time, if you are working with headings, it is important to know if it is True, Magnetic or Compass.
One more thing
Since and aircraft flies in air, and the air is usually moving, you have to correct your heading for wind as well.