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8 - Magnetic heading, the compass heading corrected for magnetic deviation but not magnetic variation; thus, the heading reliative to magnetic north. 9, 10 - Effects of crosswind and tidal current, causing the vessel's track to differ from its heading. A, B - Vessel's track. TVMDC,AW is a mnemonic for converting from true heading, to magnetic ...
A magnetic compass aboard an aircraft displays the current magnetic heading of the aircraft, i.e., the aircraft's directional orientation 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 heading indicator (also known as the directional gyro, or DG) displays the aircraft's heading in compass points, and with respect to magnetic north when set with a compass. Bearing friction causes drift errors from precession , which must be periodically corrected by calibrating the instrument to the magnetic compass.
6 – Magnetic variation, caused by variations in Earth's magnetic field. 7 – Compass heading or compass course, before correction for magnetic deviation or magnetic variation. 8 – Magnetic heading, the compass heading corrected for magnetic deviation but not magnetic variation; thus, the heading reliative to magnetic north.
Some more expensive heading indicators are "slaved" to a magnetic sensor, called a flux gate. The flux gate continuously senses the Earth's magnetic field, and a servo mechanism constantly corrects the heading indicator. [4] These "slaved gyros" reduce pilot workload by eliminating the need for manual realignment every ten to fifteen minutes.
At high latitudes, where the Earth's magnetic field dips downward toward the magnetic poles, the gyro data can be used to correct for roll-induced heading errors in the fluxgate output. It can also be used to correct for the roll- and heel-induced errors that often plague fluxgate compasses installed on steel vessels.
An attitude and heading reference system (AHRS) consists of sensors on three axes that provide attitude information for aircraft, including roll, pitch, and yaw.These are sometimes referred to as MARG (Magnetic, Angular Rate, and Gravity) [1] sensors and consist of either solid-state or microelectromechanical systems (MEMS) gyroscopes, accelerometers and magnetometers.
The formula to determine the compass heading to an NDB station (in a no wind situation) is to take the relative bearing between the aircraft and the station, and add the magnetic heading of the aircraft; if the total is greater than 360 degrees, then 360 must be subtracted. This gives the magnetic bearing that must be flown: (RB + MH) mod 360 = MB.