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| Aeroplane compasses | |
Pete Gummerson  22nd Jun 2012 14:15:22 | I have been learning about gyro compasses in my classes at college and I was wondering what do aeroplanes use for headings. Do they use a magnetic compass or do they have a gyro compass that points to true north? I would imagine large commercial aircraft may have a gyro but small cessnas and beachcraft may just use a normal magnetic compass and use a GPS unit for the true magnetic course.
Also would ATC give headings in true north or magnetic north? Hope you could answer my question, from Pete |
Zack Iddo   22nd Jun 2012 16:02:59 | I would just like to say that large commercial jet lines when flying close the the north pole will flick their switch from magnetic N to true N this is so that if they are flying from Canada to Mongolia for example they don't start flying circles when they get over the pole.
Atc nearly always give headings in magnetic as there are very few airports near where pilots have to make the switch. That's about as much as I know and when people read this post I could possibly be wrong well some parts of it. |
James Nugent  22nd Jun 2012 16:52:01 | All aircraft will have a minimum equipment list of what instruments are required by law. All aircraft have Magnetic compasses, and nearly all light aircraft have a gyro-driven Direction Indicator (DI), basically the instrument you'd see on the C172 panel in FSX! Airliners have a more advanced version, like the Navigation Display you'd see in A320/B737s etc.
These gyros, as you might have learned, drift. They need to be synced by the pilot every 10-15mins with the magnetic compass. The reason for the gyro is that magnetic compasses are quite difficult to use in operation. They are subject to acceleration and turning errors that make them difficult to use. ATC will give headings in degrees Magnetic. Zack is correct about aircraft operating in high latitudes using True North as their heading reference. The Magnetic Variation is the difference between Magnetic and True North. It is very large near the poles so they will switch to True North as the reference. In northern Canada for example, you will see runway signs that say "167T-347T", meaning that the runway hdg is 167/347 degrees True. Because the magnetic poles move over time, the charts that are used for navigation are aligned with the Geographic North Pole/True North, and indicate places of equal Mag Variation with lines called Isogonals. |
| Pete Gummerson 22nd Jun 2012 18:40:36 | Thank you very much for the information guys I really appreciate it.
Fortunately on the ships you we may just use true north thanks to the gyro compass but we still have to check for compass error at least once a watch (a watch is normally 4 hours) or after a change on course. We are able to check for errors by taking bearing from the sun, planets or stars and then check it in a nautical almanac and do seaman's magic to find out if both our gyro and magnetic compasses are out. Hope all is well from Pete |
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