Aircraft Inertial Guidance Systems

Here is a simple explanation of aircraft inertial guidance systems,
for all those who wonder how in the world
the pilot can find Honolulu when flying from Anchorage
in the middle of the night.

I was once on such a flight, wondering about this very thing when,
two hours out over the Pacific, we had to turn back
because the guidance system had failed.
I still don't know how we made it back to Anchorage,
unless maybe we had connected ourselves
to the airport by a long string.
(by DVA)
(author of the rest is unknown)

The aircraft knows where it is at all times. It knows this because it knows where it isn't. By subtracting where it is from where it isn't, or where it isn't from where it is (whichever is the greater), it obtains a difference, or deviation.

The Inertial Guidance System uses deviations to generate error signal commands which instruct the aircraft to move from a position where it is to a position where it isn't, arriving at a position where it wasn't, or now is. Consequently, the position where it is, is now the position where it wasn't; thus, it follows logically that the position where it was is now the position where it isn't.

In the event that the position where the aircraft now is, is not the position where it wasn't, the Inertial Guidance System has acquired a variation. Variations are caused by external factors, the discussions of which are beyond the scope of this report.

A variation is the difference between where the aircraft is and where the aircraft wasn't. If the variation is considered to be a factor of significant magnitude, a correction may be applied by the use of the autopilot system. However, use of this correction requires that the aircraft now knows where it was because the variation has modified some of the information which the aircraft has, so it is sure where it isn't.

Nevertheless, the aircraft is sure where it isn't (within reason) and it knows where it was. It now subtracts where it should be from where it isn't, where it ought to be from where it wasn't (or vice versa) and integrates the difference with the product of where it shouldn't be and where it was; thus obtaining the difference between its deviation and its variation, which is a variable constant called "error."

Brought to you by the
Commercial Air Transportation Agency for
Specific Traffic Regulations Over-sight of
Peripheral Hyper-Integrated Electronic Systems
[DVA made up this part, too!]
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