Compass Systems Flashcards
What is the purpose of an Aircraft Compass?
Provides aircraft heading referenced to Magnetic North
Why is True North used as a Navigation Reference?
True North never moves and is used on maps and charts
What are the three desired properties of a compass system?
Horizontality, Sensitivity, Aperiodicity
What correction is applied to a compass magnetic reading to give True North?
The correction is known as the angle of variation, which is the angular difference measured from true north to magnetic north at any given position on the Earth’s surface.
What are the two aircraft magnetic effects that can reduce the accuracy of a compass?
Hard iron, Soft iron
What are the effects of soft iron?
Earth’s magnetic field, DC current in electrical components on an aircraft, weapons or cargo
What are the effects of hard iron?
Vibration caused by riveting, aircraft stationary for a long time, engine vibration, certain equipment fitted, lightning strike
What is the purpose of the MDU?
To sense the horizontal component of the Earth’s magnetic field and to update the DG with magnetic north information
What does the annunciator indicate?
MDU is monitoring gyro and they are de-synchronised
How does the Gyro Magnetic Compass operate?
The slaving loop compares the headings of the MDU and the DG with an error sensor. If the headings are different, a gyro precession signal is produced and fed to the DG motor which applies a gyro precession of 2 degrees per minute until the error falls to zero.
What is the purpose of the ‘DG Servo loop’ used in a GMC?
To drive the display pointer or compass card
When would a compass swing need to be undertaken?
When the schedule requires it, when the compass system is in doubt, after a heavy landing
What do the following displays indicate on the annunciator?
(a) MDU is monitoring gyro and they are synchronised
(b) MDU is monitoring gyro and they are de-synchronised
(c) MDU is monitoring gyro and they are de-synchronised
(d) MDU is no longer monitoring the gyro and is using DG heading only
Where is the MDU located?
Wing tips or the fin
Describe the effect on compass headings affected by a Q, P or R magnetic force component.
Q is north and south and uses coefficient C; P is east and west and uses coefficient B; R is all headings and uses coefficient A
