From my notebook - some fix page data that you might be interested in ...
FMC FIX Page stuff
Interesting page, FIX. Much misused and misunderstood. Here are a couple of interesting limitations.
The range circles have a maximum value of 511nm. This is 2 ^ 9 and is a computer thing. 2 ^ 8 (2 to the power of 8) is a recognized number and equals 256 (Think RAM). The 2^9 is a numeric processing limit of the processor employed (equivalent to a Intel 486 for those interested) and is of course 512. Why 511? – well 0 to 511 is just that.
When you generate a Bearing Line it also has a finite dimension. In this case 699.9 nm. There is a lovely story that goes with this. It is not absolutely true, but it does make the point.
We are talking about the old English expression Plain Sailing. Now in common usage this phrase has come to mean something straightforward and easy. In its’ original form it was an expression used in navigation (Plane Sailing). The origin dates back to our old friend Gerardus Mercator (1512-1594).
Prior to the mid 16th century, voyages of any length were really just a case of – “take a lot of food and water and we will see you when we see you”. But as is the case with many of the major changes in history, a whole lot of important developments came together at about this time. The back stave gave way to the sextant. Chronometers became reasonably reliable and maps were becoming more than just fancy interpretations of even more fantastic tales. The art of (reasonably) accurate navigation was born. However it was quickly apparent that on long voyages you needed to use a Great Circle on one of Mercator’s Maps to save yourself some time and grief. But on short voyages a Rhumb Line would serve equally well. Depending upon which mathematical school you subscribe to, the limit of a Rhumb Line is 699 nautical miles. Thus the Plain Sailing expression relates to the simpler (plane) mathematics that could be applied to short voyages. Whereas the longer journeys required the more complex mathematics of the spheroid.
The Fix page generates a straight line, so this is a reasonable limitation. Future updates, I am (well ?) reliably informed, will have the BRG line limit increased to 1200+ nm. It will then have to be a curved line to show a great circle. I will be suitably impressed when I see this. Older (non Pegasus / PIP FMCs have a limit of 400 nm on this BRG line). This info is just for interest. All newer FMCs are PIP/Pegasus.
This 699.9 nm limit is also reflected in our ability to generate impromptu waypoints. You cannot take a Range/Bearing offset from a database point to beyond 699.9 (call it 700 for cash – some allow that) nm – try it.