Clarifying Information: Learning About Deviations in Magnetic North and the Role of Compasses

Clarifying Information: Learning About Deviations in Magnetic North and the Role of Compasses

Soaring the right way calls for a keen eye on some key references as we delve into the world of aviation. Known as the magnetic heading, understanding this concept is vital for a smoother journey from point A to B. Today, we'll talk about magnetic heading, how it's calculated, where to find it, and some common slip-ups to avoid during flights.

What is Magnetic Heading in Aviation?

Magnetic heading is simply the direction your aircraft is pointed, based on a magnetic compass. Uncommon as it may seem, it's essential to know that the magnetic compass isn't pointing towards the same North Pole you might find on a globe. The magnetic compass will always align with the North magnetic Pole, while the Geographic North Pole is a different location altogether.

Now, let's go over the basics of how magnetic heading works:

A compass needle in any aircraft will point towards the magnetic north pole, which serves as a datum. By determining where we're pointing in relation to this datum, we get our magnetic heading. This compass bearing is measured in degrees, with the circle divided into 360 parts. This way, each small increment is one degree.

Cardinal Point

We can give examples based on the table below for each magnetic heading cardinal point:

Magnetic Heading

| | || --- | --- || Cardinal Point | Magnetic Heading || North | 0°/360° || North East | 045° || East | 090° || South East | 135° || South | 180° || South West | 225° || West | 270° || North West | 315° |

To illustrate, if you're flying east, it can also be said that your magnetic heading is 90°. Alternatively, we can say you're flying at a 90° angle from the datum of magnetic north.

North

Luckily, we aren't confined to just these 8 headings—there are 360 of them!

0°/360°

How to Find the Magnetic Heading?

Locating your magnetic heading is a simple task made possible by reading your aircraft's compass. The compass displays the direction in degrees from magnetic north. The information can be found through a small thin line called the lubber line, which rests above your actual magnetic heading. Rest assured, your aircraft will certainly come equipped with a compass!

North East

According to Chapter 14, part 91 of the Code of Federal Regulations, all aircraft for VFR (Visual Flight Rules) flight must have a magnetic direction indicator.[5] Nonetheless, there may be other instruments on board providing similar information but with greater accuracy.

045°

Diving into the Heading Indicator

Navigating with a compass can be tricky due to its instability, especially in a fast-moving aircraft. Early flyers had no choice but to rely on the compass for computing their magnetic heading, but skilled engineers came up with a solution – the gyro-driven heading indicator.

East

The Heading Indicator, known as a direction indicator (DI) or directional gyro, offers a clear advantage over the compass in terms of stability and ease of reading. It isn't affected by magnetic interference and doesn't oscillate as much, making it more reliable in flight.[6] So, let's see how the heading indicator works:

090°

The DI's internal gyroscope provides stability. If you're curious about the physics behind it, the axis around which the gyroscope spins remains fixed in space, pointing wherever we aim it. In our case, we aim it at magnetic north.

We 'cage' or 'slave' the gyroscope so that the axis aligns with the magnetic north. This allows us to measure our magnetic heading accurately in relatively stable conditions. However, there are a few points to be careful about while flying a magnetic heading:

South East

Let's introduce you to the concept of variation and how it affects aerial navigation.

135°

What is the Difference Between Magnetic Heading and True Heading?

Do you think there's only one North Pole? Guess again! For navigation purposes, there are actually two North Poles to be aware of: Magnetic North and True North.

South

Magnetic North

180°

Deep within the Earth lies a vast quantity of metals, creating a magnetic field. All magnetic fields have poles, and the magnetic north pole, which the compass needle points towards, is currently situated in the northernmost parts of Canada. Interestingly, the magnetic pole moves slightly each year, meaning that the compass needle would point in a slightly different direction, even if you stood still.[7]

As pilots, our instruments always point to the magnetic north pole. It's important to note that the compass reading differs significantly from the Geographic North pole. In fact, the difference between these two locations is currently about 310 miles![7]

South West

True North

225°

True north refers to the point on the Earth's axis around which it revolves. The longitudinal lines on navigational charts all meet at the true north, and we calculate our headings based on these lines when plotting a route. When considering the North and South poles, people often think of the Geographic North Pole, located more than 1,000 miles away from the Magnetic North Pole.

The disparity between magnetic North and True North necessitates the concept of variation, an essential component in aerial navigation.

West

Understanding Variation and How to Apply it When Flying

270°

The variation, or the difference between true north and magnetic north, can vary greatly depending on your geographic location. In some areas, the difference is insignificant, while in others, it's substantial.

For example, if you were flying around Ocala, Florida, the difference is approximately 2°. However, if you were flying to San Jose, California, the difference is around 17°![8] Neglecting to account for this variation can lead to significant navigational errors.

North West

Navigational charts depict variation with a faint dashed line and an annotation, such as "3°E." Pilots must apply a correction, either subtracting or adding the variation to the headings measured on the chart, to achieve an accurate magnetic bearing for flight based on their location. Here are simple phrases to remember for calculating a course to fly and converting the true bearings to magnetic headings:

315°

• "Variation EAST, magnetic LEAST" - If the variation annotation features the letter "E," we must subtract the variation from the course measured on the chart to give an accurate magnetic bearing to fly.
• "Variation WEST, Magnetic BEST" - If the variation annotation features the letter "W," we must add the variation from the course measured on the chart to give an accurate magnetic bearing to fly.

For example, let's say the true course measured on the map is 195°. With a variation of 17°W, we would apply the following calculations:

• "Variation west, magnetic best."
• True Course (195°) + Variation (17°) = 212°
• Magnetic bearing to fly: 212°

Or, in case the true course measured on the map is 101°:

• True Course (101°) - Variation (12°) = 089°
• Magnetic bearing to fly: 089°

It's that simple!

Magnetic Heading and Flying | 5 Important Things to Be Aware Of

Avoiding common mistakes while using magnetic heading is crucial for safe and accurate navigation. Here are five aspects of magnetic heading to be mindful of when flying:

1. Instrument Error
2. Although compasses and direction indicators are generally reliable, they can still be influenced by factors like metal objects and electrical currents, leading to inaccurate readings.[9]
3. Conduct a thorough preflight inspection to ensure that no metal objects or electronic equipment impact your compass or direction indicator readings.
4. Acceleration Error
5. Even though rare, compasses have a tendency to "turn" to the north when accelerating and south when decelerating.[10]
6. When computing turns using the compass for magnetic heading, take a direction reading only during stable, straight, and level flight.
7. Headings and Meteorological Information
8. Air traffic control clearances, runway markings, and headings are all based on magnetic headings.[11]
9. However, meteorological information is typically given in degrees true. Be sure to convert all non-aviation meteorological information to magnetic headings for accurate weather-related navigation.
10. Apply the Right Correction for Variation
11. A common navigation pitfall is incorrectly applying variation in calculations, toggling between subtracting when we should add, or vice versa.
12. Double-check your flight log to ensure accurate calculations and avoid navigation errors.
13. Parallax
14. A minor yet recurring error when using directional instruments is parallax, which can result in inaccurate readings from the lubber line.[12]
15. To minimize parallax errors, always read the lubber line directly and verify instrument readings frequently.

By paying careful attention to these aspects, you can confidently navigate with magnetic heading and ensure a smoother flight experience. Happy flying!

Enrichment Data:[1] Magnetic Interference: https://www.flightguideabc.org/aviation-terms-Flightlevel/Magnetic-Interference/[2] Heading Indicator Drift: https://www.technomics.com/blog/wp-content/uploads/2021/07/Directional-gyro.pdf[3] Environmental Factors: https://www.faasafety.gov/files/SR_ {};[4] Cybersecurity Risks: https://www.faa.gov/about/office_org/headquarters_offices/ate/technical_publications/media/asec5000-424a.pdf#page=206;[5] Chapter 14, part 91 of the Code of Federal Regulations: https://www.ecfr.gov/cgi-bin/text-idx?tpl=/ecfrbrowse/Title014/49/part_83[6] Heading Indicator vs. Magnetic Compass: https://www.skybrary.aero/index.php/Heading_Indicating_System_%28HIS%29[7] Magnetic North Pole Movements: https://www.nationalgeographic.org/encyclopedia/north-magnetic-pole/[8] Variation: https://skyvector.com/[9] Compass Error Sources: https://www.flightguideabc.org/aviation-terms-Flightlevel/Compass-error-sources/[10] Acceleration Error: https://www.asu.cas.edu/content/heading-error-factors[11] Metric Wind Conversion: https://meteorologyonline.com/wind-direction/[12] Parallax: https://www.seaplane-flying.info/instrument-flying/accuracy-navigation-gyros/

In aviation, the magnetic heading is the direction an aircraft is pointed, based on a magnetic compass, which aligns with the North magnetic Pole, a different location from the Geographic North Pole.

To locate the magnetic heading, pilots read their aircraft's compass, where the compass displays the direction in degrees from magnetic north. Navigating with a compass can be tricky due to its instability; therefore, skilled engineers developed the gyro-driven heading indicator, also known as a direction indicator (DI) or directional gyro, which offers stability and ease of reading without being affected by magnetic interference or oscillation.

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