Have never seen VOR accuracy expressed using a confidence interval, but I guess there has to be one in there somewhere. Have seen GPS accuracy expressed in this way.
I think the VOR transmitter is +- 1 deg, and the VOR receiver must be +- 3 deg, which works out to around +- 4 deg total acceptable 'lack' of accuracy. If you are 4deg off, by using basic trigonometry you can calculate the distance from the transmitter when you will find yourself outside an 8nm wide airway. 4 / TAN(4 deg). This works out to be about 51nm.
At this point the airway will cease to be 8nm wide and will extend outwards by 4.5 deg from the transmitter. FAR 71.75 describes, no doubt a similar reg is found elsewhere too.
Last edited by slim_slag; 31st Aug 2005 at 10:27.