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Maybe time to change from Magnetic to True?

In the last US AOPA mag there is an article suggesting that, given the rate of the movement of the magnetic N Pole, we should move to true headings, true bearings for runways, etc.

How would that be done?

There is no device which can simply point to true North - apart from a gyro which is accurate/sensitive enough to detect the earth's rotation.

Administrator
Shoreham EGKA, United Kingdom

GPS can right?

EGTK Oxford

That one is easy. You use the World Magnetic Model

http://en.wikipedia.org/wiki/WorldMagneticModel

to compute the variation at a given lat/lon/alt, and then correct a magnetic north sensing device to give you true north. Of course, some problems will remain the same as with a conventional compass (sensitivity to stray magnetic fields, problems at high latitudes), but thanks to true 3D field sensors, the inclination induced problems go away.

In flight you get the true track from your area navigation equipment anyway.

The WMM is what everyone uses, your GPS to give you magnetic track, Jeppesen to draw the variation lines in the charts, and so on.

BTW, if you have two GPS antennae, you should be able to measure true heading using GPS. About one meter distance (base line) between the antennae should suffice, if you have a receiver that uses differential techniques. So this is well within what is technically possible on small aircraft.

http://www.oxts.com/default.asp?pageRef=61

Good luck getting this through EASA certification 8-)

BTW, if you have two GPS antennae, you should be able to measure true heading using GPS.

I read about that, but WAAS/EGNOS is out for any general use, and when it was tried with two GPSs at the two ends of an airliner, the result was only just good enough.

GPS can right?

Only in motion.

Administrator
Shoreham EGKA, United Kingdom

GPS can, right?

Only in motion.

If no motion is left, navigation is a secondary concern.

(sorry Peter, couldn't resist)

More on topic: Here in Western Europe I think this is an intellectual exercise only. The difference between mag and true bearing is smaller than the tolerance of our compasses ( +/- 5 degrees, ISTR?) so it matters little whether I steer 272 true or 272 magnetic.

Using true bearings would at least save a/d operators from painting other numbers on the runways every so many years.

EBZH Kiewit, Belgium

I read about that, but WAAS/EGNOS is out for any general use, and when it was tried with two GPSs at the two ends of an airliner, the result was only just good enough.

I don't think you need EGNOS for that. But you need a special purpose receiver that does carrier wave correlation. Like the receiver I posted the link.

What could be a problem is reflection on some metallic surfaces of the aircraft.

Wishful thinking, never happen in our lifetimes.

KUZA
Administrator
Shoreham EGKA, United Kingdom

Maybe it will prompt a long overdue change – The GPS will become the official primary recognised and certified navigation instrument rather than the compass.

LKTB->EGBJ, United Kingdom
56 Posts
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