Description
A magnetic compass aboard an aircraft displays the current magnetic heading of the aircraft, i.e., the aircraft's direction of travel relative to the Earth's geomagnetic field, which has a roughly north-south orientation. The compass can be used in turns to verify the aircraft is travelling in the desired direction at the conclusion of a turn. The nature of the instrument and the alignment of the magnetic pole of the earth cause the magnetic compass to have several significant limitations when used for navigation. A pilot aware of those limitations can use the compass effectively for navigation. The compass continues to operate despite failures in the electrical, vacuum or pitot static systems.
Compass turns (turns using the compass as the primary reference instrument) are not standard practice in modern aircraft. Compass turns are typically performed in simulated or actual failures of the directional gyro or other navigational instruments. A magnetic compass is a simple instrument when the compass is not moving and is on the earth. A magnetic compass installed in an aircraft is subject to compass turning errors during flight. Pilots must compensate for errors introduced by these errors.
Most of the errors inherent in the heading indications of a magnetic compass are related to the compass' construction. An aircraft compass consists of an inverted bowl with a magnetized bar attached. The bowl is balanced on a low friction pin. The bowl and pin assembly is enclosed in a case filled with non-acidic kerosene. The magnetized bar tends to orient the assembly with the local geomagnetic field. The bar turns the visible bowl of the compass. The outside surface of the bowl includes markings to indicate a magnetic heading. As the aircraft (and the compass housing) turns, the bowl remains somewhat stationary with respect to the earth due to the magnetic attraction. In summary, the aircraft is free to turn around the stationary bowl.
The standard practice when flying with a gyro-stabilized compass (or heading indicator) is to read the magnetic compass only while in straight and level flight. This reading is then used to set the gyro-stabilized compass. The gyro compass will read correctly in a turn, whereas the magnetic compass can't be read properly while turning. Thus the pilot will always ignore the magnetic compass while turning, but periodically check it in straight and level flight.
Read more about this topic: Aircraft Compass Turns
Famous quotes containing the word description:
“The Sage of Toronto ... spent several decades marveling at the numerous freedoms created by a “global village” instantly and effortlessly accessible to all. Villages, unlike towns, have always been ruled by conformism, isolation, petty surveillance, boredom and repetitive malicious gossip about the same families. Which is a precise enough description of the global spectacle’s present vulgarity.”
—Guy Debord (b. 1931)
“The great object in life is Sensation—to feel that we exist, even though in pain; it is this “craving void” which drives us to gaming, to battle, to travel, to intemperate but keenly felt pursuits of every description whose principal attraction is the agitation inseparable from their accomplishment.”
—George Gordon Noel Byron (1788–1824)
“An intentional object is given by a word or a phrase which gives a description under which.”
—Gertrude Elizabeth Margaret Anscombe (b. 1919)