Hi y'all,Debut post!I was running a non-precision GPS approach excercise in a Beech Baron from Computer Pilot magazine (May '04 issue), and I ran into a disparity between where my activated GPS approach flight plan wanted me to fly and the direction ATC wanted me to fly.This was at KPDX (Portland) after leaving the holding pattern. ATC had confirmed that I was planning on doing the GPS approach to 28L. But, while they were turning me one way, the GPS on autopilot was trying to steer me straight towards the Final Approach Fix. Well, ATC was having none of that and kept demanding that I "expedite" my turn to their heading immediately or suffer their wrath. I did as I was commanded and lined for the approach according to ATC. While I was on the final approach to the FAF, I turned the GPS autopilot back on and it didn't really even steer me to the right runway, kind of just toward the terminal.So, my questions are:1. Why the disparity between ATC and and activated GPS approach?2. If the GPS just steers you straight at the FAF and not line you up for it, as per the magenta line, why use it?3. Am I supposed to use the NAV or APR button on the autopilot once I have activated the GPS approach, and when do I press it?Also, I did have the GPS/NAV selector switch set to GPS.Any help you can provide would be greatly appreciated. I think I have run into this problem before with ATC and GPS not agreeing on where I should go, so it must be human error on my part.Thanks! Berated by ATC, led astray by GPS

In the flight simulator, it is probably best not to interface with ATC during practice approaches. ATC uses only the ILS or visual approaches.As far as using the GPS stored approaches, the following should be set:A/P : EnabledNAV/GPS : GPSA/P Nav : EnabledYou need to select, load, and activate the approach in the GPS under the PROC button. If you have a flightplan entered, the approach will be added to the bottom of the flightplan. One thing to remember is the GPS will not control your altitude. You must fly the altitude portion of the approach manually.If you select the A/P APP button with the NAV/GPS in the GPS position, it will try to fly to the airport LAT/LON and not the approach to the runway.You might try practicing using an ILS approach, set both in the GPS and the NAV1 radio. In that case, set the NAV/GPS switch to NAV, the A/P - Enabled and A/P APP - Enabled. In this case the GPS is providing backup situational awareness on its graphics display for the approach you selected.W. Sieffert

Great advice!! Thanks! I knew it had to be something wrong on my part. I think having the A/P APP button on with the NAV/GPS set to GPS is what did me in. I appreciate it!BillStill berated by ATC, but not being led astray anymore.