Magnetic Compass
Magnetic Compass
Lesduur is: 120 minOnderdelen in deze les
Magnetic Compass
Open with the idea that a magnetic compass still works without aircraft electrical power because it responds to Earth's magnetic field rather than GPS or radio signals.
Today’s learning goal
I can explain how a magnetic compass works, identify its main parts, and describe variation, deviation, and movement-related compass errors.
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One word or phrase you connect with a magnetic compass
Use this to surface prior ideas such as direction, north, navigation, magnet, heading, cockpit, or backup instrument. Briefly pick out accurate ideas and misconceptions to revisit later.
Navigation starts with direction
Aircraft need a reliable way to show heading
A magnetic compass gives direction without complex electronics
It works by responding to Earth’s magnetic field
This makes it a basic but important navigation instrument
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Earth is a giant magnet
Earth produces a magnetic field
A compass contains a magnetic element
That element aligns with the field
The indication shows the aircraft’s heading reference
Stress that the compass is not receiving a signal. It is reacting physically to Earth's magnetic field.
How the compass works
Earth’s magnetic field → magnetic element responds → element aligns with the field → pilot reads the heading.
Keep this conceptual. There is no need to go into deep magnetic-field physics at this stage.
Inside the compass
Magnetic element: responds to Earth’s field
Pivot: allows movement
Compass card: displays heading
Damping fluid: reduces unwanted movement
Lubber line: reference for reading heading
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What the compass responds to
Not GPS satellites
Not radio signals
Not the engine alone
It responds to Earth’s magnetic field
This is a useful misconception check before moving into true north and magnetic north.
What does a magnetic compass respond to?
Radio signals
Earth’s magnetic field
GPS satellites
Engine power
Targets the key misconception check from slides 2–6: the compass is a physical magnetic instrument, not a signal-based system.
How a compass works
A magnetic compass works because Earth produces a magnetic field. Inside the instrument, the magnetic element responds and aligns with that field. The pilot then reads the heading using the compass display.
All answers come directly from the opening mechanism explanation and labelled parts. This anchors the load-bearing vocabulary before moving to north references.
True north
True north is the direction of the geographical North Pole
It is based on Earth’s geographical axis
Maps and charts use true north as a reference
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Magnetic north
A magnetic compass aligns with Earth’s magnetic field
So it points towards magnetic north
Magnetic north is not the same as the geographical North Pole
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Two different norths
True north and magnetic north are different directions
The angle between them has a specific name
That angle is called variation
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Variation
Variation is the angular difference between true north and magnetic north at a particular location.
Linked to Earth’s magnetic field
Changes with location
Reinforce the memory rule: variation = Earth.
What causes variation?
Variation is caused by Earth, not the aircraft
It exists because magnetic north and true north do not match
Different places can have different values of variation
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What is variation?
Turn-related lag
Aircraft interference
Angle between the two norths
Compass fluid movement
The correct answer checks that students distinguish variation from deviation and from dynamic errors.
Why does a compass not point to true north?
Expected elements: true north is geographical; magnetic north is where the compass aligns; they are different because a compass follows Earth’s magnetic field rather than the geographical pole.
The aircraft affects the compass too
The compass sits inside an aircraft environment
Electrical wiring can influence it
Radio equipment can influence it
Ferrous and metal components can influence it
Some engine-related components can also have magnetic effects
Let students see that even a simple instrument is affected by its surroundings.
Deviation
Deviation is compass error caused by magnetic effects produced by the aircraft itself.
Electrical equipment
Radio equipment
Ferrous materials
Other aircraft components
Reinforce the memory rule: deviation = aircraft.
Variation and deviation
Variation = Earth
Deviation = Aircraft
Variation comes from the difference between true north and magnetic north
Deviation comes from magnetic influences within the aircraft
Keep terminology exact and consistent here because students often swap these two terms.
Examples of each error
Geographic north compared with magnetic north → variation
Earth’s magnetic field differing by location → variation
Radio equipment affecting the compass → deviation
Aircraft metal structure affecting the compass → deviation
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Which situation is an example of deviation?
Radio equipment affects it
Norths differ by location
Charts use true north
Earth causes the angle
Distractors are all variation-related ideas from the surrounding slides, so students must make the Earth/aircraft distinction accurately.
Variation or deviation
Variation is linked to Earth and describes the angle between true north and magnetic north. Deviation is linked to the aircraft and is caused by magnetic effects from equipment or metal structure inside it.
Reinforces the lesson’s memory rule: variation = Earth, deviation = aircraft.
Which aircraft source seems most likely to interfere with the compass?
Electrical wiring
Radio equipment
Metal structure
Engine components
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Can we trust the compass?
A magnetic compass is useful, but its reading is not perfect.
Errors can come from:
Earth’s magnetic field
Aircraft magnetic effects
Turning
Acceleration
Deceleration
Use this as the bridge from static errors to movement-related errors.
Dynamic errors
When the aircraft moves, the compass may temporarily show an indication that does not match the expected heading.
This can happen during:
Turning
Acceleration
Deceleration
Emphasise the word temporary. Students may otherwise assume the instrument has failed.
Turning error
During a turn, the compass may lag behind or lead the expected heading
The indication does not settle instantly
This does not automatically mean the compass is broken
Explain conceptually: the magnetic system has physical characteristics and does not instantly settle during manoeuvres.
Acceleration and deceleration
When the aircraft speeds up, the compass indication can temporarily change
When the aircraft slows down, the indication can also change
The compass can be affected by how the aircraft is moving, not only by where it is pointing
Separate heading from speed change. Students often assume any compass change means the aircraft has turned.
Heading matters
Compass behaviour can be especially noticeable on northerly and southerly headings
The effect is often discussed with turning, acceleration, and deceleration
At this stage, focus on the principle rather than detailed rules
Only go into detailed northerly turning and acceleration rules if the course specification requires it.
A turn does not always mean failure
A pilot may begin a turn and see the compass briefly disagree with the expected heading
A likely cause is dynamic compass error
A more stable heading reference can come from a directional gyro or heading indicator
Clarify that gyro-based heading references are generally steadier in manoeuvres, but they also need checking and have their own limits.
A compass briefly disagrees during a turn. What is the best explanation?
The compass has failed
The map is incorrect
A temporary dynamic error
Variation has disappeared
Checks that students recognise movement-related errors as temporary and not automatic instrument failure.
Movement-related errors
During a turn, the compass may lag or lead the expected heading. During acceleration or deceleration, the indication can also change. These are temporary errors caused by aircraft movement.
Echoes the wording from slides 17–21 and consolidates the idea that movement, not just direction, affects the indication.
What should a pilot consider if the compass shifts in a turn?
Expected elements: the aircraft is manoeuvring, so dynamic error can occur; the compass is not necessarily broken; a directional gyro or heading indicator can provide a steadier reference.
Key ideas to remember
A magnetic compass uses Earth’s magnetic field
Variation is caused by Earth
Deviation is caused by the aircraft
Aircraft movement can create temporary compass errors
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What is one idea from today that you will remember?
Reflection only. Invite brief personal responses about the most memorable concept, rule, or distinction from the lesson.
What helped you understand the compass best today?
Reflection only. Encourage students to name a specific explanation, example, or visual that helped them understand the topic.
Which part still feels hardest or most confusing?
Reflection only. Useful for diagnosing whether students still confuse variation, deviation, and dynamic error.
Glossary
magnetic compass - an instrument that shows direction by aligning with Earth’s magnetic field
magnetic field - the invisible magnetic influence produced by Earth or magnetic materials
heading - the direction in which an aircraft is pointing
true north - the direction of the geographical North Pole
magnetic north - the direction a magnetic compass aligns towards
variation - the angular difference between true north and magnetic north at a particular location
deviation - compass error caused by magnetic effects produced by the aircraft itself
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Glossary
compass card - the marked card that displays direction on the compass
magnetic element - the magnetised part of the compass that aligns with Earth’s field
pivot - the point that allows the compass system to move freely
damping fluid - liquid inside the compass that reduces excessive movement
lubber line - the fixed reference mark used to read the heading
dynamic error - a temporary compass indication error caused by aircraft movement
directional gyro - a gyro-based instrument used as a more stable heading reference during manoeuvres
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