Why magnetic?

[MasterBates]

I´d really like to start a argument here:

Modern aircraft don´t need to use magnetic bearings to get around. Why doesn´t the aviation industry just quit the use of reference to the magnetic poles, they are constantly moving and are troublemakers, and stick to true instead of magnetic. We could of course have the spiritus forte compass and when in doubt would use it to verify our heading (even though the Sun is more accurate (not the newspaper)).

This doesn´t represent my opinion, but what won´t be done for the sake of a good argument
:8

MB.

[timzsta]

The argument is true for a sophisticated airliner with and IRS that can sense things like the earths rotation, coriolis effect and so on and so can tell well true north is. A remote indicating compass can be used as an alternative, and it will sense very accurately, the direction of magnetic north and is a cheaper alternative.

For a great deal many other aircraft such equipment is not fitted. Where would you put an IRS or remote sensing compass in a Cessna 172 for example, or other light aircraft, and how much would it cost?

Although the magnetic poles move, the rate of change is so small as to have little effect. We are talking the odd degree a year. Now most people cant fly to an accuracy of 1 degree over a period of sixty seconds, so you can see the effect is neglible.

[Tinstaafl]

Hey! I resent that slur. I can hold a heading for at least 65, sometimes 70 seconds...

[jed_thrust]

Master Bates (you wouldn't be from the dark blue, by any chance?): this is something that has given me some thought over the years. After some 14 years in the Navy, where we flew true all the time (not too many nav aids out there...) it almost hurts to sit in a modern airliner with triple IRS and double GPS and see everything being converted BACK to magnetic, just to fly direct-tos most of the time!

GA is a different matter: money counts.

[p290951]

I agree with the last post. On my flight test, I could hold a heading for ever. I passed didn't I

[OzExpat]

Sorry MB but you won't get an argument out of me on this issue either. It's been said that modern air navigation technology go to a lot of trouble to emulate the 17th century. It's true that modern nav systems such as IRS and GNSS don't need a magnetic reference at all. They work in true and use a built-in algorithm to convert true to magnetic for the pilot's benefit.

But it's strictly a "comforter" that is intended to imply that the pilot has some measure of control over his (or her) destiny. Magnetic reference had its uses and, for GA, probably still does - at least until Regulators bite the bullet and adopt GNSS as the standard nav facility. Then, just plug it into your autopilot and happily fly the exact same track - maybe even a bit more precisely...? :D

IMHO, reliance on magnetic reference breeds further reliance when there is no longer a need for it. Sadly, there is currently no end in sight to this perceived dependence. :{

Looks like you'll have to come up with another topic for an argument... :p

[twistedenginestarter]

It's not correct to say cost is a factor. A £100 GPS will give you true course so all navigation could be expressed in true. You might still have a magnetic compass in a Cessna 150 to give you a rough idea which direction you are pointing when stationery and you could use if it you want to fly a track manually. If your chosen track was 137 true and you were pointing 130 magnetic but tracking 133 true, you could guess holding 134 magnetic might do the trick. You don't actually need to know what magnetic direction you are heading - it could be in radians. The compass would just be a convenient datum to help you achieve your true track as shown by the GPS.

[MasterBates]

jed_thrust. No, I´m not from the Navy even though my name could indicate that, some long and lonely evenings with the boys in the middle of the Pacific.
I see there is really no point going true until GA has gotten into the 20th century, huh.:O

[bookworm]

Why do you need (angular measurement of) tracks at all? In every situation I can think of, you want to fly to a point, not in a particular direction.

To fly on a straight line to that point, all you need is a datum against which you can turn left or right to hold or regain that line. It doesn't really matter which datum you use, so you might as well use the cheapest -- for many users that will be magnetic.

[OzExpat]

Yes, bookworm, reality will continue to rule the market, so it's fair to say that magnetic compasses and magnetic courses are going to be with us for a long time yet. That's sad, but I guess that all old traditions die hard. :sad:

[FlyingForFun]

Well, I'll take the bait, I suppose.....

As has been pointed out by other posters, GA still relies on magnetic headings. (It is not true that a GPS will give you a true heading. It may give you a true track, but not a true heading, and the two can be very different. Besides which, many people fly without a GPS.)

It would certainly be possible for air transport to operate on true headings, and GA to work on magentic headings. But could you imagine the headache that would cause ATC? Isn't it far easier to have everyone working off the same reference?

It's very easy to get the equipment on an airliner to convert true headings to magentic. It's much harder to get the equipment on a typical light aircraft to convert magnetic headings to true. Therefore, the lowest common demoninator is the magnetic heading, and that's why we all use it.

FFF
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[Blacksheep]

Wotya gonna use when all else fails? The 'quiet dark cockpit' concept does go to the extreme sometimes. Not very often but sometimes....

**************************
Through difficulties to the cinema

[Spodman]

Australia's Eurocats 2000 system (similar to NATS) has all the enroute consoles oriented to true north, and our bearing/range line thingie reads in degree true also. To give an aircraft a heading we visualise the true heading and convert it to magnetic, just to avoid confusion when the aircraft converts it back to true.:confused: :confused:

Egad!

Why use true on the consoles? For example we can have variations of more than 24 degrees east AND more than 27 west on the one console. Usually a bit less than that, but, and he doesn't do much vectoring.