Mxsmanic wrote:
Tim writes:

Not all planes have GPSes. In fact, most don't.

That depends on what category of aircraft you're looking at.

Doesn't matter what category you are looking at. We've still
got transport aircraft with just steam gauges.


Many of the haldheld units fail.

How many? I've never seen one fail, although I'm sure it happens
occasionally. They don't even have any moving parts.

I've had them fail lots of times. All it takes is the battery to go doead.


The failure rate for compasses is quite low.

So is their accuracy, even when they are functioning perfectly.

Accurate enough. Reliable...never really have seen one fail.

Not really. It is unreliable. Its signals can be disrupted - rendering
them useless.

Magnetic bearings are constantly disrupted, everywhere on Earth.

Between your ears primarily.

You have an engine turning. That's power. And it can fail, just like
electrical power.

That power only propells the aircraft. There's no guarantee that it
provides electricity for avionics. I can tell you that I've been
in a number of aircraft where it did not, either by malfunction or
DESIGN.


Not in the real world. On a computer maybe...

Even in the real world. The purpose of INS is to have a way of navigating
without any external references; it's a very advanced and accurate
implementation of dead reckoning.

CHORTLE. Have you any experience with a real INS. A real INS can't
find squat without being told where it is starting from. This has
to be boostrapped from other navigational devices. It's long term
stability isn't any better than a compass. It needs additional
input.

It's useless for truth north unless you have a chart _and_ you know where you
are. Even for magnetic north, it can be substantially off. And just knowing
which way is north doesn't help you much, anyway.


Your GPS and INS are useless without a chart or their internal
electronic equivelent.