11.5.3 Instruments- Compasses Flashcards
What must be installed in a position where it can be seen from both pilot stations?
Direction indicator, non stabilised magnetic compass.
What is the indicated heading?
The angle between the aircraft’s longitudinal axis, which is shown with the lubber line, and the direction to the North Pole.
What is true heading?
True north based on geographic north pole
What is the difference between magnetic north and true north?
2000km
What is the angle between true north and magnetic north called?
Variation
How much does magnetic north move a year?
40 miles per year
How often does Jeppesen update their maps?
Every 56 days
What is inclination?
The field lines decline to the earths surface.
What are names for the horizontal and vertical components of the magnetic field?
Isogonal and Isoclinic
At latitudes above 70 degrees the horizontal component is so weak that a compass is not useable, what should be used instead?
Directional gyro or inertial stabilised system.
What is hard iron magentism?
Permanent form of magnetism, caused by the presence of iron or steel parts in the structure.
What does the effect of hard iron magnetism have on the aircrafts compass?
Bar magnets lying longitudinally, laterally and vertically around the compass position.
To analyse the effect of hard iron the imaginary bar magnets are annotated as?
Component P,Q and R
What is soft iron magnetism?
Temporary form of magnetism caused by the magnetically soft metallic parts of an aircraft.
What does the effect of soft iron magnetism depend upon?
The aircrafts heading and the local angle of dip.
Soft iron magnetism: what is a positive deviation?
Deflecting the compass to the right. (Easterly)
Soft iron magnetism: what is a negative deviation?
Needle deflects to the left. (Westerly)
What is the only electrical part in a direct reading compass?
Light
In commercial aircraft what is the direct reading compass called?
Standby
What is the lubber line and what does it do?
Vertical line on the standby compass that shows the heading on a rotating compass scale.
When is there no influence on the heading direction of the standby compass?
When going north or south.
What happens to the standby compass when the aircraft accelerates?
It shows a lower heading.
How can deviation be minimised?
Using small adjustable magnets inside the compass called compass compensation.
During compass compensation set up how often is the deviation recorded?
Every 90 degrees.
What is the B coefficient during compass compensation?
Difference between the east and west deviations, divided by 2.
What is the C coefficient during compass compensation?
Difference between the north and south deviations, divided by 2.
For a B correction where does the aircraft normally stay pointing?
Easterly
For a C correction where does the aircraft stay pointing?
Northerly
What is coefficient A?
A constant error which is the same on all headings.
How is an error in coefficient A corrected?
Rotating the compass or changing the compass card.
What is coefficient B?
Varies as a function of the sine of the compass heading. It is usually associated with fore-and-aft permanent magnetism.
How is coefficient B corrected?
Using fore and aft magnets
What is coefficient C?
Varies as a function of cosine of heading.
What is coefficient C usually associated with?
Athwartship and permanent magnetism.
What does Athwartship mean?
Across the aircraft from side to side.
How is coefficient C corrected?
With athwartship magnets.
What kind of cased light is used in a magnetic compass to avoid deviation?
Brass, with contra-wound filament.
What is a flux valve?
Magnetic sensory device that electrically transmits the information to the aircrafts system.
What does a flux valve ‘Z’ mean?
Vertical intensity
What does a flux valve ‘F’ mean?
Total intensity
What does a flux valve ‘X’ mean?
North
What does a flux valve ‘Y’ mean?
East
Where is the flux valve located?
Far away from all magnetic fields of the aircraft.
How does the pilot monitor the flux system?
With a slaving annunciator
What two modes of operation does the flux valve have?
Slave and free
What does free mode do in a flux capacitor?
Flux valve disconnected so it does not monitor or auto realign.
What does slave mode mean in the flux system?
Default mode, connected and working to information provided by the flux valve.
In the flux system how many Hz is the excitor energised with?
400Hz
In the flux system where does the output of the coils go?
Selsyn Unit
What does a selsyn unit do?
Compares the detected magnetic heading with that indicated on the instrument.
After a compass swing the cumulative deviation must not exceed…?
5 degrees
Why do modern aircraft not need compass swings?
Because they have INS and GPS.
