Understanding the Use of Compass in Aircraft Navigation

When it comes to aviation, knowing how to use a compass is one of the basic tasks you should know. In this post, we will discuss the Earth’s magnetic field, where the main core actually is and the effect of this variation on the compass equipped the aircraft. Using a magnetic compass is highly recommended by tenured pilots despite the development of GPS driven EFIS navigation system available. This is required, so you would know how to navigate your aircraft in case of emergency or GPS technical difficulties.

To give you further information, we will focus on that subject in simpler terms. We will educate you more about the using of compass, maps, clock and other basic primary navigation methods. We will also discuss the function of radio-satellite navigation as these things are still crucial in today’s aviation field.

Magnetic and True North

First thing you need to know is that the Earth is rich in iron to the point you can actually see it as a very large magnet—that being said, the magnetic field is not really in constant state as iron concentrations are not distributed evenly. Even the magnetic North Pole is not really located where the true North Pole is. This is what they call the variation or declination of force due to the movement of the magnetic pole it points you.

Unknown variation

It could be really challenging for anyone who is using a magnetic compass when you can track the variation of your location. Take note that the magnetic lines that usually take the north to south direction is parallel near the equator but may also shift to the ground near the poles. This is called the inclination or dipping process. When this happens, an error may occur in the higher latitudes—for example, near the North or South Pole since the magnetic North Pole is not even fixed in one location. As the National Geophysical Data Center mentions, it is actually moving in the northwest with a speed of 40 km per year.

In the same process, a compass may align itself with the magnetic lines around the planet. As mentioned earlier, this however does not interpret that it is pointing directly to the true north. To accurately get the true north, you need to adjust the compass by its local magnetic declination or variation. Today, there are also online tools you can use as a variation calculator. You just need key in the location and obtain the current magnetic declination or variation.

Correcting for true bearing

Now, to acquire the true bearing from a compass, you should add the variation from your location to the compass bearing. Take note however when you compute from magnetic to true, the west variations are negative while the east is positive.

Runway heading

When the aircraft lines up on the runway, verify the compass indication is against the runway numbers. This is just to make sure that you are on the correct runway and that the compass hasn’t failed.

Runway numbers (RWY 24) are chosen based on the magnetic heading within 10° for that runway. So that a runway with a magnetic heading of 242° will be designated as 24. Wind reports from the tower controller are also based on the magnetic direction the wind is blowing from. This makes is very easy to assess the crosswind component by the pilot.