Magnetic Compass & It's Uses
The magnetic compass is one of the oldest instruments installed in an airplane and in many older aircraft it's the only direction seeking instrument. To determine direction, the compass uses a simple set of two magnets, each with two poles. The magnets are mounted to afloat so they pivot freely in AL line with the earth's magnetic field.
Aircraft compasses are considered wet compasses because their cases are filled with liquid, in this case kerosene. The liquid also helps to stabilize the magnets and keep them from rocking around too much, especially when the aircraft encounters turbulence. Attached to the float is a compass car, which labels all 300 and 60 degrees of heading for the pot to reference, similar to the heading indicator, the last zero digit has been removed from the label. To coincide with the card is a reference line called a lubber line positioned in the center of the window, so the pilot knows specifically what heading they are flying.
You may notice that the compass card looks backwards. In fact, if you compare the compass to the heading indicator, you'll notice that they turn in opposite directions. This is because when you're looking at the compass, you're actually looking at the backside of the instrument, so everything must be reversed.
The compass is normally used as a backup source of heading information, while the gyroscopic heading indicator is used as the primary heading reference. If your heading indicator fails and you understand the limitation of the magnetic compass, you should be able to navigate properly. When you are referring to a compass for heading information, remember that it is accurate only when your airplane is in smooth air and in straight and level unaccelerated flight.
Aircraft compasses are considered wet compasses because their cases are filled with liquid, in this case kerosene. The liquid also helps to stabilize the magnets and keep them from rocking around too much, especially when the aircraft encounters turbulence. Attached to the float is a compass car, which labels all 300 and 60 degrees of heading for the pot to reference, similar to the heading indicator, the last zero digit has been removed from the label. To coincide with the card is a reference line called a lubber line positioned in the center of the window, so the pilot knows specifically what heading they are flying.
You may notice that the compass card looks backwards. In fact, if you compare the compass to the heading indicator, you'll notice that they turn in opposite directions. This is because when you're looking at the compass, you're actually looking at the backside of the instrument, so everything must be reversed.
The compass is normally used as a backup source of heading information, while the gyroscopic heading indicator is used as the primary heading reference. If your heading indicator fails and you understand the limitation of the magnetic compass, you should be able to navigate properly. When you are referring to a compass for heading information, remember that it is accurate only when your airplane is in smooth air and in straight and level unaccelerated flight.