The
greatest cross track error acceptable is 5nm off the airway centreline.
We assume
that the aircraft flies out of one beacon and then switches over half way to
home to the next beacon so the greatest possible error will occur at the half
way point.
The 1 in
60 rule can be used here.
Expressed
as a formula it is:
distance off
track = track error angle
distance gone 60
or,
distance gone = distance off track x 60
track error angle
The
maximum distance off track is 5nm, track error angle
is 5.5º so
distance to half
way = 5 x 60 ÷ 5.5 = 54.5nm
distance between
the beacons is twice that, 109 nm.