Compass Presentation

5/27/2018 Compass Presentation

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Malaysian Institute of Aviation Technology


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Navigational ChartLines of Longitude are lines drawn from North to South.

The Prime Meridian is the lines of Longitude and is recognized by angle of0.

All lines of Longitude are known as Meridians.

Lines of Longitude are drawn from 1 to 179 E and 1 to 179 W.

Lines of Latitude are lines drawn from East to West.

The Equator which is 0 is a good example of Line of Latitude.

Lines of Latitude can be drawn up to 90 S and 90 N.


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Terrestrial Magnetism

The earth behaves as though it contains a cylindrical bar magnet.

The magnetic poles are about 90 miles away from true or geographicalpoles.

Its north pole in the southern hemisphere and south pole in the northernhemisphere.

A freely suspended compass needle or bar magnet aligns itself parallel tothe earths magnetic field.

The compass needle will stand vertical at the poles and horizontal atthe equator.

The magnetic meridian is the direction in horizontal plane of the freelysuspended compass needle influenced only by the earths magnetic

field. The angle of dip is the angle between the horizontal and a freely

suspended compass needle influenced only by the earths magneticfield.


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Terrestrial Magnetism


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Definitions

ACLINIC LINE (magnetic equator)

The line along which all points have zero dip.

ISOCLINAL

The line along which all points have equal dip.

ISOGONAL

A line on the surface of the earth along which all points

have the same variation.

AGONIC LINE

A line on the surface of the earth along which all points

have nil variation.


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Variation

Also known as Magnetic Declination - The angle between magnetic northand true north at a particular location.

Isogonic LineA line on a chart connecting points of equal magneticvariation - easterly or westerly.

AgonicAn imaginary line on the earth's surface connecting points where

the variation is zero.


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Deviation

The angular difference betweenmagnetic heading and compass

heading due to magnetic

influences in or near aircraft

caused by surrounding metalsand electrical accessories.

It is called Easterly (positive

deviation) or Westerly (negative

deviation).

Corrected by adjusting

compensator magnet and

residual deviation on compass

correction card or steer by card.


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Compass

To indicate the aircraft heading with respect to Magnetic North.

It is a north seeking device.

Magnetic attraction to the earths magnetic field.

Commonly used compass on aircraft are: Direct reading compass or magnetic compass also called

standby compass if it is not used as a primary heading

reference.

Remote indicating compass or slave compass.


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Magnetic Compass

A self contain instrument that didnot require external source.

A freely suspended bar magnetwill have one of it end pointing tomagnetic North.

In flight when aircraft changesheading, the compass casing willmoves according to aircraftdirection.

The compass remain stationary

and a new heading will be viewedon the compass card.

the lubber line is to reduceparallax error.


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Magnetic Compass

A compass card or float which is mounted on jeweled bearing. It hasnumbers and direction markings so that the magnetic heading of the aircraftcan be read from the instrument.

The case is filled with a light oil (refined kerosene) which dampens floatmotion and lubricates the bearing.

A diaphragm or bellows accommodates thermal expansion and contraction.

The compensator is two small moveable magnets used to adjust thecompass for deviation error.

The lubber line is a marker against which readings are taken.


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Remote Indicating Compass

A heading indicator that is fitted onto the instrument

panel.

It is not a self contain device.Heading information is slave to the flux valve or

directional gyro.

Flux valve which sense the earths magnetic field are

located at a remote area of the aircraft where there isleast magnetic disturbances.

The heading indicator is called Gyro Compassor Slave

Compass.


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Remote Indicating compass

Consist of:Flux valves/flux gates Located where there is least interference of magnetic deviation. It sensed the direction of the earth magnetic field.Directional gyro unit To provide heading signal to the compass system base on

gyroscopic rigidity.Slaving amplifier To slave the directional gyro to the flux valve when it is in compass

mode.Servo amplifier To detect any errors and feed to servo network to balance the

circuit.Heading indicator Mounted on the instrument panelCompass controller Mode selector switch (DG or Slave) Annunciator (show system synchronization) Set-heading knob (set heading manually)


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Slave Compass


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Slave

Compass


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Slave Compass


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Horizontal Situation Indicator

Also known as Course DeviationIndicator (CDI)

Combine Heading (Slaved GyroIndicator) with VOR and Glideslope

Indicator.Represent aircraft's heading andthe aircraft's position in relation toany beacon tuned in on the NAV1receiver.

The Heading bug is triangular andthe Course bug is pointed.

Warning flag (NAV, HDG, GS) willcomes on if system failed.
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Horizontal Situation Indicator


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Radio Magnetic Indicator (RMI)

Its displays magnetic heading and bearing indication in a single indicator. Heading information is from slave compass system.

ADF and VOR is from airfield non-directional beacon (NDB).

ADF will show direction (to and from) of the designated airfield.

VOR will show the exact heading of the designated airfield.


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Compass and Compensation Definitions

Calibrationmeans the measurement of residual deviations of a compassinstalled in an aircraft.

Compensationmeans the correction of deviations resulting from

magnetism in an aircraft.

Deviationmeans the angle required to be added algebraically to acompass reading to obtain the aircraft magnetic heading.

Direct reading compassmeans a compass which has the magnetic

sensing element and heading indication located in the one instrument.

Remote indicating compass means a compass system which has the

magnetic sensing element located remotely from the indicator(s) together

with gyroscopic means to stabilise or smooth the heading indications.

Standby compassmeans a direct reading compass which is not used as

the primary heading reference.


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Compass Swing

Observing the compass reading on different headings of the

aircraft.

Calculating the deviation errors and determining coefficients.

Neutralising the magnetic field of the aircraft by adjusting thecompensator devices.

Recording any residual deviations.

Deviation recorded on the steer by card must not be more

than 5 for light aircraft, 3 for large aircraft. Deviation card should be in interval of 30 on light aircraft

and 45 for large aircraft.


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Condition that required compass swing

After flying through electrical storm or strike by lightning.

After any modification, repair or major component change involvingmagnetic material.

Calendar date due.

Suspect error reading.

After modification in the vicinity of flux detector.

Electrical/radio installation in vicinity of flux detector.

Whenever a compass been subjected to shock.

After magnetic crack detection check.

After ferrying freight load of magnetic influence. Aircraft has been in long term storage.

Whenever the sphere of operation of the aircraft is changed to one ofdifference magnetic latitude.


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Preparation before Swinging

To be carried out on a Compass Rose or Compass Base.

area free from any magnetic interference.

Aircraft operator and airport authority are responsible to do survey.

Set aircraft to level flight condition.

engine running control surfaces to be in normal straight and level flight

electrical equipments switched onradio, instruments, pitot tube heater

cockpit area to be free from any magnetic material.

Technician involved will be free from magnetic material items on their body.

Non-magnetic tool to be use when adjusting compass compensator.


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Compass Swing Procedure

Datum compass should be align with aircraft longitudinal axis at a distanceof 50150 feet.

Sighting of aircraft longitudinal axis is indicated by two plumb bobssuspended fore and aft of the fuselage or by referring to vertical stabiliser.

On compass rose, align the plumb bob or vertical stabiliser with the

marked line. Aircraft heading on the cardinal and quadrantal points offset by 5 deg isallowed.

Before taking compass reading, allow short pause between each headingand tapped compass gently.

Records all reading on a proper record forms.

Adjust coefficient C, B, ADeviation card to be raised.

Detail of aircraft type and registration, compass type and serial number,place and date to be recorded on the back.

Compass swing to be recorded in the aircraft log book.


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Compass Rose


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Compass Rose


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Compass Rose


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Compass Swing Gears


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030

Windowstile

Tail

To 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 the

reference compass is adjusted horizontally before reading.

Prism


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Compass Swing Cardinal and Quadrantal Points


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Deviation Compensation and Recording


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Steer by Card (Large Aircraft)


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Steer by Card (Small Aircraft)


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