Airbus Nav Data Track Headings

[OBK!]

for airbus drivers.

Not sur if this is on FMS1 and FMS2 because I've only really noticed on the old corroded bus's but looking at charts (sid/star/enr), the airways/leg tracks seem to be coded differentley in the FMS than what's published. Say about 2 degrees. A lot of people seem to be happy with this, but if it's wrong it's wrong? Anyone else seen this? It's not just on one aircraft but over a fleet of airbus.

T16 for example has been coded in the FMS as 3 degrees off from what's on the Jepp Enr Chart....nav accuracy low this could be a problem?

[J.O.]

There can be an error due to the length of the airway segment. I've seen 2 to 3 degrees on several occasions with long airway segments. Yet the airplane always seems to fly over the correct waypoints, and other aircraft seem to be on the same track.

[enicalyth]

In most instances magnetic angles are printed on the chart except at latitudes/locations where magvar considerations make it more sensible to print true values.
Either way the angle at each end of the track won't necessarily be the reciprocal of the other. Over long distances we prefer to fly geodesic paths and north-seeking needles do not actually point directly to the Magnetic North Pole until you are very, very close. So there may be a slight (1 degree?) inconsistency every now and then between paper and glass. But stop a moment. Surely waypoints et al are strictly defined by latitude and longitude and not by the whims of geomagnetism or how many stubbies the cartographer had for lunch?
I don't think for a moment that the preferred mode of navigation in a modern transport aircraft is predicated on paper and glass magnetic values. Might it not have more to do with a suite of inertial and radio aids that attempt to place the aircraft on geodesic paths on a largely known spheroidal earth between points whose coordinates are fixed?
Don’t obsess with magnetic values even when it comes to the hemispherical rule. Depending on whether ones instinctive oath is to say merde or sh!t there have to be exemptions of one sense or another and fun to be had if drinks are not to be spilled. So it will be writ somewhere in the AIS in such a way that you can only find it when you don’t need to.
If you don’t like what the compass says, hang your jacket over it and never trust your instruments if your tie points at the ceiling. Based on not much more than this I never landed at the wrong airfield.
Alas for Jepps they are nowadays almost strong enough to make paper darts. Dost thou remember when they were illegible blue flimsies but of strength sufficient for certain, ahem, sedentary purposes? Now you couldn’t do THAT with Aerads!

[Scallywag]

Hi OBK

Have also noticed this on some older A320/321 but not on A330. The only sense I can make of it is the old Honeywell ADIRU variation table has been obsolete since 2000 and so the variation in it's database for given lat/long is years out of date. There is an OEB and TR which give details of airfields where you can no longer carry out autolands because of this, including some of our bases. Of particular note for my company are BFS (Jan06), GLA (Mar06), NCL (APR 07), and MAN (Jul 07), in 4 affected aircraft.

Check TR 32 in FCOM 3.01.22 page 4 for up to date list if it affects you.