Magnetic Compass

• New lesson editor
• Physics
• Further Education (Key Stage 5)

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.

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

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

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?

A

Radio signals

B

Earth’s magnetic field

C

GPS satellites

D

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.

magnetic field

magnetic element

heading

radio signal

pivot

altitude

engine

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

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

Two different norths

• True north and magnetic north are different directions

• The angle between them has a specific name

• That angle is called variation

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

What is variation?

A

Turn-related lag

B

Aircraft interference

C

Angle between the two norths

D

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

Which situation is an example of deviation?

A

Radio equipment affects it

B

Norths differ by location

C

Charts use true north

D

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.

Earth

aircraft

metal structure

turning

GPS

location

heading

Reinforces the lesson’s memory rule: variation = Earth, deviation = aircraft.

Which aircraft source seems most likely to interfere with the compass?

1

Electrical wiring

2

Radio equipment

3

Metal structure

4

Engine components

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?

A

The compass has failed

B

The map is incorrect

C

A temporary dynamic error

D

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.

turn

acceleration

temporary

variation

deviation

permanent

north

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

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

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