Autopilot & GPS Waypoint Flight Accuracy

[Badmachine]

Is there any general reference info on the web regarding autoplilot flight, waypoint flight accuracy and any role played by flight technical errors?

[OzExpat]

I just Googled "autopilot flight" and got loads of hits that might help you. I then Googled "waypoint flight accuracy" and got a few hits that might be useful to you. As far as "flight technical error" is concerned, this is the error provision that is made in instrument procedure designs to account for pilot error and/or pilot delay in initiating a climb, descent or turn.

You can find out more about it from Volume 1 of ICAO document 8168 - Pans Ops.

HTH

[Badmachine]

Thanx for the info.



Was hoping to find more info regarding how aircraft performance (during various speeds and manuevers, etc.) can affect aircraft enroute waypoint accuracy under WAAS navigation.

WAAS alleges certain horizontal and vertical accuracy. I was hoping to learn how certain flight factors affect this accuracy. (Presumably reducing it)

[twistedenginestarter]

Can't think of anything

You seem to be asking if anything the aircraft is doing can affect GPS accuracy. I can't imagine what would. It's just using radio transmissions (GPS and WAAS) and if they are interrupted the instrumentation will report the failure.

[Badmachine]

For example, one author has described improved accuracy for curved approaches under WAAS guidance. (Presumably autopiloted flight) I thought perhaps aircraft performance or weather factors might affect approach accuracy for such approaches. If an autopilot flight plan intends for an aircraft to be at a certain waypoint during flight, it was thought that aircraft performance or weather may play a role regarding waypoint accuracy.

[SimJock]

RNAV waypoints have tolerances applied during procedure construction called ATT (Along Track Tolerance) and XTT (Cross Track Tolerance), the values of ATT and XTT are generally the RNP value of the procedure, ie RNP1 gives +/- 1nm, GPS approach 0.3nm etc. The terms are defined in PANS OPS Vol II as:

"Along-track tolerance (ATT). A fix tolerance along the nominal track resulting from the airborne and ground
equipment tolerances."

"Cross-track tolerance (XTT). A fix tolerance measured perpendicularly to the nominal track resulting from the
airborne and ground equipment tolerances and the flight technical tolerance (FTT)."

The 'airborne' bit should allow for weather/aircraft issues.