Hi Bob,

Can you please explain what the AIP reference (underlined bold sentence) below really means and how it relates to the Q3 on page 5.37 with answer [c].

A position fix is one determined by the intersection of two or more position lines which intersect with angles of not less than 45 deg. and which are obtained from NDBs, VORs, localisers or DMEs in any combination.


Thanks,

Frederik

A position line is simply a track across the map to or from your present position from an NDB, VOR or LOC. A position line by itself is not a fix, since it only tells you that you are somewhere on that line. Before you can call it a fix, you must know exactly where you are on that line. If there is a DME at the NDB, VOR or LOC, you can use it to find the distance from the aid to your present position. If you know the track you are on and also the distance you are along that track, you have a fix. See the figure at the top of page 2.22.

Also, the figure at the bottom of page 2.21 shows that a fix can be obtained from two separate NDBs or VORs as long as you are within their rated coverages and the two tracks cross at an angle greater than 45°. In that figure they cross at 90° which would be best.

If both of those aids are NDBs, they must both be within 30nm of you if you want to claim a fix. In that case, the rated coverages are not considered.

I can't find any Question 3 on page 5.37.

Bob

Thank you for the explanation Bob.
I can't seem to find the reference to the pages you have listed in the CNAV book.
The page 5.37 is Navigation Progress Test 5 and the the question was relating to which combination of nav aids would work for a position fix.

Hi there yes I’m having the same problem that is the answer in the nav book states AIP 1.1 4.1.5.1 which is not in the aip.

This is now AIP ENR 1.1 para 4.2.4