Compass

April 8, 2023April 8, 2023 By R. WarningBy R. Warning 11

April 8, 2023 By R. Warning 2

COURSE PREVIEWCOURSE PREVIEW

► TheoryTheory Earth magnetismEarth magnetism CompassesCompasses Compass errorsCompass errors

► PracticePractice Compass swing siteCompass swing site Compass swingCompass swing Alternative methodsAlternative methods


Permanent MagnetismPermanent Magnetism

► Certain materials can be magnetized, By Certain materials can be magnetized, By putting them in a magnetic field. After putting them in a magnetic field. After removing the field remnant magnetism will removing the field remnant magnetism will be kept. be kept.

NN

SS


Electro MagnetismElectro Magnetism

►Around a conductor that conducts Around a conductor that conducts electrical current a magnetic field is electrical current a magnetic field is also generated.also generated.


Earth magnetismEarth magnetism

The earth can be seen The earth can be seen as a giant magnet. as a giant magnet. The magnetic poles The magnetic poles however do not align however do not align exactly with the exactly with the geographic poles.geographic poles.

The exact place of the The exact place of the magnetic poles is not magnetic poles is not constant, but varies constant, but varies in time.in time.


Magnetic VariationMagnetic Variation

Magnetic variation is Magnetic variation is the angle at a certain the angle at a certain point on earth point on earth between the between the magnetic north and magnetic north and the true north. Due to the true north. Due to the fact that the place the fact that the place of the magnetic north of the magnetic north is not fixed, the is not fixed, the variation changes. In variation changes. In Holland about one Holland about one degree every six degree every six years.years.

True NorthTrue North

Magnetic northMagnetic northVariationVariation


The variation is not a function of the geographical The variation is not a function of the geographical position, But can vary due to changes in the earths position, But can vary due to changes in the earths rock formations. Lines of equal variation around the rock formations. Lines of equal variation around the globe are so called isogonics lines.globe are so called isogonics lines.


Variation must always Variation must always be added to the be added to the magnetic heading magnetic heading to get the true to get the true heading!heading!

Variation is positive if Variation is positive if the true north is to the true north is to the right (east) of the right (east) of the magnetic north. the magnetic north. Else it is negative.Else it is negative.

++

M. NorthM. North

T. NorthT. North

variationvariation


Inclination (magnetic dip)Inclination (magnetic dip)

The direction of the magnetic The direction of the magnetic force at a certain point on force at a certain point on earth is not always exactly earth is not always exactly horizontal. Only at the horizontal. Only at the equator. At the poles they equator. At the poles they are nearly vertical. The are nearly vertical. The angle of force line with the angle of force line with the horizontal is called the horizontal is called the inclination or dip angle.inclination or dip angle.

A magnetic compass uses only A magnetic compass uses only the horizontal component of the horizontal component of the earths magnetic field. the earths magnetic field. But the inclination tends to But the inclination tends to tilt a magnetic compass.tilt a magnetic compass.

InclinationInclination


Inclination cardInclination card


IntensityIntensity

The strength off the earth magnetic field is not constant on all places on The strength off the earth magnetic field is not constant on all places on earth. earth.

The strength of the magnetic field is measured in oersed. In the The strength of the magnetic field is measured in oersed. In the Netherlands the earths magnetic field is about 0.471 oerstedNetherlands the earths magnetic field is about 0.471 oersted


CompassesCompasses


Aircraft compassesAircraft compasses

There are tree kinds of aircraft There are tree kinds of aircraft compasses.compasses.

1.1. Direct-reading compasses or standby Direct-reading compasses or standby compassescompasses

2.2. Remote-reading compasses systems Remote-reading compasses systems with a flux valvewith a flux valve

3.3. Inertial compass systemsInertial compass systems


Direct-reading compassesDirect-reading compassesThe Direct-reading compasses is a The Direct-reading compasses is a

free turning magnet with a free turning magnet with a scale around it, mounted on a scale around it, mounted on a pivot inside a liquid. The liquid pivot inside a liquid. The liquid provides damping for the scale. provides damping for the scale. Normally a silicon liquid is Normally a silicon liquid is used. The center of gravity of used. The center of gravity of the scale and the magnet the scale and the magnet assembly is well below the assembly is well below the pivot point. So that the pivot point. So that the compass will mainly react to compass will mainly react to the horizontal component off the horizontal component off the earth magnetic field. The the earth magnetic field. The liquid is sealed off by a liquid is sealed off by a membrane to compensate for membrane to compensate for volume differences due to volume differences due to temperature changes. temperature changes. Underneath the compass is a Underneath the compass is a compensator unit to allow compensator unit to allow adjustments to the compassadjustments to the compass


The compensator unitThe compensator unit

There are two compensators inside There are two compensators inside the compensator unit. One for the compensator unit. One for Longitudinal axis off the aircraft Longitudinal axis off the aircraft and one for the cross-axis. Each and one for the cross-axis. Each compensator consists of two compensator consists of two bars that can be turned in bars that can be turned in opposite direction. In each bar opposite direction. In each bar two small compensator magnets two small compensator magnets are mounted.are mounted.

In neutral position the magnetic In neutral position the magnetic forces of these magnets oppose forces of these magnets oppose each other, giving a resultant each other, giving a resultant field of zero. When the bars are field of zero. When the bars are turned, the resultant force will turned, the resultant force will be added to the earths be added to the earths magnetic field, But of course magnetic field, But of course only the vector part that is only the vector part that is parallel to the earths field.parallel to the earths field.


NN

SS SS

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Earths fieldEarths field

Compensator fieldCompensator field

Resultant fieldResultant field


Direct-reading compasses Direct-reading compasses errorserrors

There are two main errors involved in There are two main errors involved in using a direct-reading compass in an using a direct-reading compass in an aircraft.aircraft.

1.1. Northern turning error.Northern turning error.

2.2. Acceleration errorAcceleration error


Northern turning errorNorthern turning errorThe compass card is mounted so that its The compass card is mounted so that its

center of gravity is well below the pivot center of gravity is well below the pivot point. When the aircraft is in a banked point. When the aircraft is in a banked turn, the card also banks because of turn, the card also banks because of centrifugal forces. While the card is in the centrifugal forces. While the card is in the banked attitude, the vertical component banked attitude, the vertical component of the earth’s magnetic field causes the of the earth’s magnetic field causes the compass to dip to the low side of the turn. compass to dip to the low side of the turn. The error is most apparent when turning The error is most apparent when turning trough headings close to north and south. trough headings close to north and south. When the aircraft makes a turn from a When the aircraft makes a turn from a heading of north, the compass briefly heading of north, the compass briefly indicates a turn in the opposite direction. indicates a turn in the opposite direction. Passing trough south, the compass leads Passing trough south, the compass leads the turn considerably. As the aircraft nose the turn considerably. As the aircraft nose passes though the west, the compass passes though the west, the compass should approximate the correct heading. should approximate the correct heading. Then, as the aircraft nose approaches Then, as the aircraft nose approaches north again the compass lags.north again the compass lags.

In the Netherlands this error is 2,5° with a 1 ° In the Netherlands this error is 2,5° with a 1 ° bank and 25 ° with a 10 ° bankbank and 25 ° with a 10 ° bank


Acceleration errorAcceleration errorA second way to tilt the compass card out of A second way to tilt the compass card out of

the horizontal plane is to accelerate or the horizontal plane is to accelerate or decelerate the airplane. With the card decelerate the airplane. With the card mounted with its CG below the pivot, mounted with its CG below the pivot, acceleration causes the card to tip acceleration causes the card to tip forward. In the Northern Hemisphere forward. In the Northern Hemisphere where the magnetic field has a where the magnetic field has a downward component, this causes the downward component, this causes the north-seeking tip of the compass needle north-seeking tip of the compass needle to swing downward.to swing downward.


Other compass errorsOther compass errorsBesides the dynamic errors (northern turning error and acceleration error.) and the errors Besides the dynamic errors (northern turning error and acceleration error.) and the errors

caused by the aircraft it self (for witch we will calibrate the compass.) there are some caused by the aircraft it self (for witch we will calibrate the compass.) there are some minor faults in direct-reading compasses.minor faults in direct-reading compasses.

► Scale faults caused by an unjust calibration of the scale.Scale faults caused by an unjust calibration of the scale.► Collimination faults, caused by a difference between the magnetic axis of the compass Collimination faults, caused by a difference between the magnetic axis of the compass

and the north of the scale.and the north of the scale.► Lubber line alignment error.Lubber line alignment error.► Liquid swirl error. If there is not enough room in the compass housing, the scale will be Liquid swirl error. If there is not enough room in the compass housing, the scale will be

turned with the aircraft, due to the viscosity of the compass fluid. turned with the aircraft, due to the viscosity of the compass fluid.

The first 3 errors will be eliminated when the A error is adjusted during the compass swing.The first 3 errors will be eliminated when the A error is adjusted during the compass swing.


Checking a direct reading Checking a direct reading compass:compass:

•Pivot friction test:Pivot friction test: With the use of a small magnet, make the With the use of a small magnet, make the compass rotate 10compass rotate 10° keep it in this position for 10 seconds. Remove the ° keep it in this position for 10 seconds. Remove the magnet an let the compass come to a rest. Note the heading. Do the magnet an let the compass come to a rest. Note the heading. Do the same towards the other side. Again note the heading. The difference same towards the other side. Again note the heading. The difference between the two observations should not be more than 2 between the two observations should not be more than 2 °.°.

•Damping test:Damping test: With the use of a small magnet make the compass With the use of a small magnet make the compass rotate 90 °. Keep it in this position for one minute. Take the magnet rotate 90 °. Keep it in this position for one minute. Take the magnet away. The compass should turn back with in 5 ° of its original heading away. The compass should turn back with in 5 ° of its original heading with in 10 seconds.with in 10 seconds.


The remote reading compassThe remote reading compassThe remote reading compass, in Fokker aircraft called the AHRS (or IRS, but they do not work The remote reading compass, in Fokker aircraft called the AHRS (or IRS, but they do not work with the earths magnetic field), is basically a directional gyro system connected to a flux valve. with the earths magnetic field), is basically a directional gyro system connected to a flux valve. To adjust the gyro heading indication automatically.To adjust the gyro heading indication automatically.

The flux valve is normally mounted in an area as free as possible The flux valve is normally mounted in an area as free as possible

Magnetic disturbances. Mostly in the wing tips.Magnetic disturbances. Mostly in the wing tips.

On Fokker aircraft the flux valve is mostly indexed. That meansOn Fokker aircraft the flux valve is mostly indexed. That means

that the flux valve can not be turned, to removethat the flux valve can not be turned, to remove

a possible A error. This indexing is a factory setting.a possible A error. This indexing is a factory setting.

The flux valve consists of a double 3 spoke transformer with inThe flux valve consists of a double 3 spoke transformer with in

each Spoke a pick off coil and one exciter coil per pair of spokes.each Spoke a pick off coil and one exciter coil per pair of spokes.

The exciter coil saturates the spokes, so that static magnetic fieldThe exciter coil saturates the spokes, so that static magnetic field

in each of the spokes is transformed to a alternating field.in each of the spokes is transformed to a alternating field.

The strength of this field is a function of the earths magneticThe strength of this field is a function of the earths magnetic

field lines passing trough the length of the spoke. Hence thefield lines passing trough the length of the spoke. Hence the

amplitude of the induced voltage is a function of the position ofamplitude of the induced voltage is a function of the position of

the spoke in the earths magnetic field. (and the intensity the spoke in the earths magnetic field. (and the intensity

off the field)off the field)

The coils are mounted on a gimbal with a led weight that keeps it The coils are mounted on a gimbal with a led weight that keeps it

Horizontal.Horizontal.


ExcitationExcitation

400Hz400Hz

Course outputCourse output

800Hz800Hz


The electric compensatorThe electric compensatorThe flux valve can be electrically compensated for B and C errors. If a small DC current is The flux valve can be electrically compensated for B and C errors. If a small DC current is

Applied in the sense windings of the flux valve. This current should generate a magnetic field that is equal in Applied in the sense windings of the flux valve. This current should generate a magnetic field that is equal in

strength as the field that caused the disturbance but opposite in direction.strength as the field that caused the disturbance but opposite in direction.

800Hz800Hz

OutputOutput

DCDC

sourcesource

Flux Flux

valvevalve

400 Hz excitation400 Hz excitation Compensator drawn for one direction Compensator drawn for one direction onlyonly


The Remote Compensator The Remote Compensator unitunit

The variable DC power source in the previous slide The variable DC power source in the previous slide is located in the remote magnetic compensator is located in the remote magnetic compensator unit.unit.

On the unit, you find also some test points to On the unit, you find also some test points to measure the DC voltage applied to the flux measure the DC voltage applied to the flux valve and a potentiometer to adjust the valve and a potentiometer to adjust the voltages. After successful adjustment of the voltages. After successful adjustment of the compass system, the voltages should be compass system, the voltages should be measured and written down on a sticker on the measured and written down on a sticker on the remote compensator unit.remote compensator unit.

This way a remote compensator unit or flux valve This way a remote compensator unit or flux valve can be replaced without the need to do a new can be replaced without the need to do a new compass swing. Only the voltages should be compass swing. Only the voltages should be taken over from the old compensator unit.taken over from the old compensator unit.

Inside the remote compensator unit is also a circuit Inside the remote compensator unit is also a circuit that transforms the tree wire output of the flux that transforms the tree wire output of the flux valve into 2-wire sine/cosine signals. And a valve into 2-wire sine/cosine signals. And a monitor circuit that’s checks the functioning of monitor circuit that’s checks the functioning of the flux valves and the remote compensator the flux valves and the remote compensator unit.unit.


Flux valve errorsFlux valve errors

Principally the flux valve suffers also from the northern turning error and acceleration Principally the flux valve suffers also from the northern turning error and acceleration errors just as the standby compass does. But because the reading of the flux valve errors just as the standby compass does. But because the reading of the flux valve output is stabilized with a directional gyro, The readout is much more reliable.output is stabilized with a directional gyro, The readout is much more reliable.


Aircraft errorsAircraft errorsDue to the fact that aircrafts contain a certain amount of iron and other magnetic material and Due to the fact that aircrafts contain a certain amount of iron and other magnetic material and

there are a lot of life wires in an aircraft. The aircraft itself will generate a magnetic field that there are a lot of life wires in an aircraft. The aircraft itself will generate a magnetic field that will disturb the precession of the compass systems. These aircraft errors or static errors we will disturb the precession of the compass systems. These aircraft errors or static errors we can divide into tree categories; Index errors, one cycle errors and two cycle errors.can divide into tree categories; Index errors, one cycle errors and two cycle errors.

Static errorsStatic errors

Index errorsIndex errors One cycle errorsOne cycle errors Two cycle errorsTwo cycle errors

A faultA fault

LongitudinalLongitudinal CrossCross

C faultC fault B faultB fault D faultD fault E faultE fault

A correctionA correction C correctionC correction B correctionB correction Not correctedNot corrected


Adjusting the compassAdjusting the compass

We have to adjust an compass for A, B and C faults. E and F faults are generally We have to adjust an compass for A, B and C faults. E and F faults are generally minor and are not compensated.minor and are not compensated.

The A fault can be compensated by turning the compass or flux-valve in The A fault can be compensated by turning the compass or flux-valve in horizontal direction.horizontal direction.

The B fault is compensated by the E-W adjustment of the compensator.The B fault is compensated by the E-W adjustment of the compensator.

And the C fault is compensated with the N-S adjustment of the compensator.And the C fault is compensated with the N-S adjustment of the compensator.

AA

CC

BB


Total deviationTotal deviation

The total deviation caused by the aircraft should be The total deviation caused by the aircraft should be

compensated by means of a compensated by means of a ► A-fault correction that is linear over the whole compass range. A-fault correction that is linear over the whole compass range. ► B-fault correction, that acts as a B-fault correction, that acts as a cosinecosine function over the function over the

compass rangecompass range► C-fault correction that’s a C-fault correction that’s a sinesine function. function.

With the B and C correctors we only adjust the amplitudes of the With the B and C correctors we only adjust the amplitudes of the sinesine

and Cosine curves. The total Compensation is the sum of the A-and Cosine curves. The total Compensation is the sum of the A-fault, B-fault, B-

fault and C fault corrections. This total correction should fault and C fault corrections. This total correction should compensate forcompensate for

the total deviation generated by the aircraft.the total deviation generated by the aircraft.


-1.5

-1

-0.5

0

0.5

1

1.5

2

A fault C fault B fault Total correction

00°° 360360°°180180°°9090°° 270270°°


The compass swing locationThe compass swing locationA compass swing must be carried out on an approved site!A compass swing must be carried out on an approved site!► An approved site should be accessible and level.An approved site should be accessible and level.► Free from magnetic fields (except earths magnetic field.)Free from magnetic fields (except earths magnetic field.)► Should be at least 46 meters away from steel framed buildings and 91 meters Should be at least 46 meters away from steel framed buildings and 91 meters

from buildings containing electrical power generation.from buildings containing electrical power generation.► Large enough to swing the aircrafts it’s intended for.Large enough to swing the aircrafts it’s intended for.

There are two compass swing site classifications.There are two compass swing site classifications.► Class 1 with a permit able deviation of ±10’.Class 1 with a permit able deviation of ±10’.► Class 2 with a permit able deviation of ±25’.Class 2 with a permit able deviation of ±25’.

Periodic re-surveyPeriodic re-survey► A class 1 site must be re-surveyed every 5 years.A class 1 site must be re-surveyed every 5 years.► A class 2 site every 2 years. (??)A class 2 site every 2 years. (??)

The surveying party must work with the standards of the Admiralty Compass The surveying party must work with the standards of the Admiralty Compass Observatory (ACO) and must be recognized by the CAA.Observatory (ACO) and must be recognized by the CAA.

(Source: CAA UK leaflet 8-1 compass base surveying)(Source: CAA UK leaflet 8-1 compass base surveying)


Swing site’s at SchipholSwing site’s at Schiphol

There is only one compass swing site at There is only one compass swing site at Amsterdam! This is the fairway near Amsterdam! This is the fairway near the Martinair hangar’s.the Martinair hangar’s.

The site near the old Fokker buildings is The site near the old Fokker buildings is not surveyed and contains a lot of iron not surveyed and contains a lot of iron in the ground.in the ground.


The Compass swingThe Compass swing

A compass swing contains two parts.A compass swing contains two parts.

1.1. The correction swing. Where the compass is calibrated and the A, B and C errors The correction swing. Where the compass is calibrated and the A, B and C errors are adjusted.are adjusted.

2.2. The calibration swing, where the remaining deviations are noted and written on The calibration swing, where the remaining deviations are noted and written on the deviation table that is mounted in the aircraft.the deviation table that is mounted in the aircraft.

Note that with a Fokker 100 with IRS systems, the IRS may be used as reference.Note that with a Fokker 100 with IRS systems, the IRS may be used as reference.

Else a approved prismatic landing compass mounted on a tripod should be used as aElse a approved prismatic landing compass mounted on a tripod should be used as a

reference. reference.

Keep in mind that, when standing in front of the aircraft with a reference compass, theKeep in mind that, when standing in front of the aircraft with a reference compass, the

reading is 180° with respect to the aircrafts heading.reading is 180° with respect to the aircrafts heading.

When reading the reference compass make sure there is sufficient distance between the When reading the reference compass make sure there is sufficient distance between the

compass and the aircraft. Take also care not to wear any iron tools, watches, radio’s etccompass and the aircraft. Take also care not to wear any iron tools, watches, radio’s etc

Be also aware that the reference compass comes also with a deviation card!Be also aware that the reference compass comes also with a deviation card!


030030

WindowWindow stilestile

TailTail

To read the reference compass, position the compass so that the window style andTo read the reference compass, position the compass so that the window style and

the vertical stabilizer line up with the compasses lubber line. Make sure thethe vertical stabilizer line up with the compasses lubber line. Make sure the

reference compass is adjusted horizontally before reading.reference compass is adjusted horizontally before reading.

PrismPrism


Preparing the compass swingPreparing the compass swing

Before a compass swing is undertaken make sure the following preconditions are Before a compass swing is undertaken make sure the following preconditions are met:met:

► Authorization of the airport authorities.Authorization of the airport authorities.► Towing facilities.Towing facilities.► Daylight!Daylight!

Make sure you have the following equipment with you.Make sure you have the following equipment with you.► A stairs to leave and enter the aircraft in the field (if there is no air stair on F100).A stairs to leave and enter the aircraft in the field (if there is no air stair on F100).► Special adjustment tool for the standby compass.Special adjustment tool for the standby compass.► Flat screw driver for “A” fault adjustment stby compass and compensator Flat screw driver for “A” fault adjustment stby compass and compensator

adjustment.adjustment.► Wrench to loosen and tighten the locking nuts on the AHRS compensator unitWrench to loosen and tighten the locking nuts on the AHRS compensator unit► Voltmeter to measure the compensation voltages on the compensator.Voltmeter to measure the compensation voltages on the compensator.► Two Porto phones to communicate between outside and inside of aircraft.Two Porto phones to communicate between outside and inside of aircraft.► Master compass and tripod or pylorus and bracket and course list.Master compass and tripod or pylorus and bracket and course list.► Correction form, deviation form and deviation cards.Correction form, deviation form and deviation cards.


The readout on the aircraftThe readout on the aircraft compasscompassThe The ReadoutReadout of the master of the master compasscompass

Start atStart at NorthNorth

Adjusted readingsAdjusted readings


Example calculationExample calculation


The calibration swingThe calibration swing

After the correction swing is performed, a calibration swing should be made. The After the correction swing is performed, a calibration swing should be made. The calibration swing is to verify the correct adjustment of the compass and to calibration swing is to verify the correct adjustment of the compass and to make a deviation list and deviation cards, to make the crew aware of the make a deviation list and deviation cards, to make the crew aware of the remaining deviation errors.remaining deviation errors.

We are making a full 360 degrees swing with 30 degrees interval. On every We are making a full 360 degrees swing with 30 degrees interval. On every interval we note the deviation of the standby compass and the two AHRS interval we note the deviation of the standby compass and the two AHRS systems and the standby compass in emergency power condition.systems and the standby compass in emergency power condition.

For the standby compass the maximal deviation may be 10 degrees but between For the standby compass the maximal deviation may be 10 degrees but between successive (30°) steps the difference in deviation may be 4° maximum!successive (30°) steps the difference in deviation may be 4° maximum!

The maximum deviation for the AHRS may be 2°!The maximum deviation for the AHRS may be 2°!

After the calibration swing aAfter the calibration swing a deviation deviation form should be filled in for tech records form should be filled in for tech records and deviation cards should be made for in the cockpit.and deviation cards should be made for in the cockpit.


The pylorus methodThe pylorus methodWith a normal compass swing a master With a normal compass swing a master

compass is used as reference. As an compass is used as reference. As an alternative a pylorus can also be used if alternative a pylorus can also be used if the compass swing site is approved for the compass swing site is approved for this method.this method.

A pylorus is an instrument with witch we can A pylorus is an instrument with witch we can very precisely measure a angle between very precisely measure a angle between two points. In our case the longitudinal two points. In our case the longitudinal axis of the aircraft and a known point at axis of the aircraft and a known point at some distance away.some distance away.

The angle between this known point and the The angle between this known point and the aircraft heading is predetermined for all aircraft heading is predetermined for all compass headings used during the compass headings used during the compass swingcompass swing

By measuring the angle with the aircraft By measuring the angle with the aircraft longitudinal axis, and comparing this longitudinal axis, and comparing this with the predetermined value, we can with the predetermined value, we can calculate the deviation.calculate the deviation.


Before we start using the pylorus, we Before we start using the pylorus, we have to align the instrument with have to align the instrument with the aircrafts longitudinal axis. This the aircrafts longitudinal axis. This is done by putting the instrument is done by putting the instrument on a known spot (cockpit side on a known spot (cockpit side window), Level the instrument and window), Level the instrument and then point the instrument exactly then point the instrument exactly to the wing tip and adjust the to the wing tip and adjust the bottom reference ring of the bottom reference ring of the pylorus to 240.25° (F50) as given pylorus to 240.25° (F50) as given on the job card.on the job card.

Now the zero should be exactly in line Now the zero should be exactly in line with the aircrafts longitudinal axis.with the aircrafts longitudinal axis.

After this we can shoot for every 30° After this we can shoot for every 30° heading a suitable target from the heading a suitable target from the target list. By subtracting the value target list. By subtracting the value given on the target list , With the given on the target list , With the actual readout on the pylorus scale, actual readout on the pylorus scale, the datum heading can be the datum heading can be calculated. calculated.

Subtract the readout heading from the Subtract the readout heading from the datum and you get the deviation.datum and you get the deviation.

Fixed distance 32cmFixed distance 32cm


NN330330

αα

αα

Value on target listValue on target list

Actual valueActual value


FocusFocus

Fine adjustFine adjust

HorizontalHorizontaladjustmentadjustment

Deviation scaleDeviation scale

longitudinal axislongitudinal axisadjustment ringadjustment ring

longitudinal axislongitudinal axisadjustment ringadjustment ring

Fixing BoltFixing Bolt

Clamps to fixClamps to fixpylorus to aircraftpylorus to aircraftwindow structurewindow structure


Leveling bubbleLeveling bubble


The EndThe End

Compass

Documents

magnetic compass

earth magnetic field

earths magnetic field

magnetic heading

magnetic poles

magnetic forces

warning inclination

compass lags