CAP 698 is a UK official document. So I would assume that 6076 feet IS the current UK and JAR value for a nautical mile. It is nothing personal, believe me! I will write whatever value they want me to use.

Another one is that one must use a Pooley's CRP-5 whizz-wheel. The last time I saw something like that was in an aviation museum. A Jeppesen CR-3 is much quicker, easier and more accurate but all the answers are predicated on using this antique CRP-5 artifact with its clumsy way of working compressibility into the equation. Sigh ...

The best one I have seen, so far, was a German test problem that had to be worked backwards to arrive at the Indicated Air Speed! Fiendishly difficult and totally pointless, since in the real world one glance at the airspeed indicator would give the answer to that.

Ok cool guys. I really enjoyed how you managed to explain pretty much everything else than what I asked about here :) - Are you all relatives of former pres. Clinton? How did you EVER get to talk about the theory of relativity??

I guess I will still be using 1852m for a nautical mile, and you can keep fighting over how many feet that is equivalent to.

God bless PPRuNe for accurate answers!

Does anyone know the numbers used by GPS algorithms for the nautical mile?

Since (1) GPS receivers work our nautical miles by measuring the distance between two coordinates (rather than an INS/IRS-style speed/time integration) - and (2) because the GPS model of the earth is quite an accurate oblate spheroid one, rather than a perfect sphere - one must assume that there is no fixed value that correlates x degrees to z feet (i.e. 1 degree = 60x6076ft or whatever).

It must rather be a variable calculation that takes into account where (i.e. latitude) those coordinates are located. In other words, the same distance travelled in degrees at the equator and at the poles would produce a (slightly) different "distance travelled" value in feet and NM.

Also, the altitude of the aircraft will have an effect, because flying the same angular distance between two coordinates will produce a greater actual distance as altitude increases. For GPS, altitude is a big deal, since the calculated geographic position on earth is merely the result of comparing the various psuedo-ranges from the satellites, which change as the aircraft altitude changes.

Mind you, not a lot of receivers will output feet as a distance unit once a certain threshold has been exceeded.

That's just my assumption. I'll check this with an authority on GPS and report back the definite answer.

This is quite an interesting point.

What a funny fellow you must be. You ask for the definition of a nautical mile, which is given to you on a platter as being, yes, derived from a certain value in metres, at least according to the CAA/JAA.

When you work it all out you get 6076 feet. That is the anwer to your original question.

What that has to do with the real world is another question because here we are in the realm of nerds, the sort of guys one would laugh at back in High School, with their thick spectacles held together at the bridge with tape and a selection of writing instruments in a plastic 'pocket protector' in the breast pocket of their wrinkled, white, short-sleeved shirt (one of five worn on successive days of the week until the weekend when they could get wild and crazy by donning a plaid flannel shirt on Saturday and a long-sleeved white one with a clip-on tie for Sunday church).

I have temporarily left the real world where I flew real airplanes for real money and never mind the niff-naff. (You have done all your take-off calculations when another passenger boards. What do you do? Correct answer: 'Recalculate everything because the performance values will have changed.' Yeah, right.) Now I am back in the domain of the nerds, and who is laughing now? Answer: they are! While I am fuming over the pointlessness (to me) of some of the questions they have already got the answer to three decimal places.

When handed lemons, make lemonade. Here one might as well learn to play nicely with the nerds. It's their ball and their rules.

Yes, reduction in latitude means the nautical mile is measured at 45oN/S