1. Should be 5 degrees (the runway is designated to the nearest 10) factored by, if anyone thinks about it, the change in variation since the runway was designated. (I don't know of any runway redesignated for variation changes, but there may well be some.)
2. Assuming that the HSI is showing magnetic headings (is it?) there should be no variance. After all, a 1 degree error would have you 3 miles off track in 180 miles flown if you use the wrong instrument. Too much, if you have no other way of establishing your actual track flown.
3. 100 feet would be the maximum; if you average the two readings you'll not be more than 50 feet out, I think, which sounds acceptable.
Actually, I've totally forgotten, if I ever knew, what the "book" rules are. So ignore the above.
Last edited by Capot; 19th Oct 2012 at 18:12.