On 02/09/06 08:09, Ron Lee wrote:
"Marco Leon" mmleon(at)yahoo.com wrote:

So how far off an airway is an aircraft when they are following a GPS flight
plan with every intersection and VOR? Is there an article or study somewhere
that includes metrics to back it up? For example, "a non-WAAS GPS-derived
line direct btween two intersection xx miles away will differ from the
airway between those same two intersections by x.x statute miles." How do
the error allowances play into this?


Since unaugmented GPS (not using WAAS) is accurate to 10 meters or so
(plus/minus) and an airway is plus/minus four MILES (or is is two?)
the navigation source (GPS) is not a major error source.

An airway is 8 miles wide (4 miles on either side of the centerline).

One of the problems is that GPS accounts for magnetic variations differently
than the VORs do. Also I don't think GPS accounts for the fact that the
VOR radial are not exactly aligned with magnetic north (what is this called?
variance? I can't remember - it's documented in the A/FD).

GPS position errors would be on top of all this.


Ron Lee


--
Mark Hansen, PP-ASEL, Instrument Airplane
Cal Aggie Flying Farmers
Sacramento, CA