If you draw a line on a map going north or 360o, that is called your true course. For magnetic navigation purposes, you must correct for variation. Remember, there's a dashed variation line on the map labeled with the number of degrees of variation and either an E or a W. If it's E, then you subtract the number of degrees indicated from your true course. If it's W, you add. Once you have determined the degree of variation, then you have to determine the compass deviation. A magnetic compass is affected by metal and/or electical field in the airplane. This is called deviation. Every plane has a compass correction card which shows the amount of deviation in the magnetic compass. In the planes BJ and Pete are using, it's pretty simple. For example, on any northerly heading that is 270o to 089, the compass correction card shows a two degree deviation or two degrees less than what it really is. This means you have to add two degrees. On southerly headings 090 to 269, the card indicates two degrees more, and you have to subtract two degrees. For purposes of this lesson, the result is the magnetic course.

QUESTIONS - BACK

Please send any comments to:
Curator: Tom.Benson@grc.nasa.gov
Responsible Official: Kathy.Zona@grc.nasa.gov