What Is a Magnetic Compass?
A magnetic compass is an instrument used to measure the Earth’s magnetic field and determine direction.
The magnetic compass installed in aircraft used to be primarily a simple device consisting of a directional magnet and a scale. Nowadays, instruments indicating direction are often derived from information obtained by a magnetic sensor located at the tip of the wing, known as a Horizontal Situation Indicator (HSI).
The direction displayed by the magnetic compass includes composite errors. Deviation represents the angle between the true North Pole and the magnetic North indicated by the compass. Variation is the angle between the magnetic North and the North indicated by the compass, also known as magnetic variation. The magnetic heading indicated by the compass is the sum of deviation and variation concerning the true North.
Errors also include dynamic errors that occur when the aircraft changes its heading or accelerates/decelerates.
Uses of Magnetic Compass
The magnetic compass installed in aircraft serves as an instrument to inform pilots about the heading of the aircraft. It has been used since the early days of aviation, comparing favorably to other instruments.
However, the direction indicated by the magnetic compass always includes errors such as deviation and variation. Pilots must correct these errors to determine the correct heading.
On the other hand, methods for aircraft to determine direction have advanced in various ways. Techniques such as relying on radio waves emitted from ground-based antennas to determine the aircraft’s position and direction or receiving signals from satellites for position and direction information have been developed and put into practical use.
Nevertheless, the magnetic compass remains an essential instrument, still installed in the cockpit today.