Date: Friday, July 13, 2001, 9:58:08 PM Subject: Flight to Scottsdale today Howdy Piper Folk, Today we started our trip, which we hope will eventually lead us to Oshkosh, but today, ends with us landing at Scottsdale (SDL), AZ, to visit our kids grandparents. This morning I helped "swing the compass", which meant precisely lining up the plane to N - W - S - E. The avionics shop owner was using this interesting compass with a sight view with which he would sight down the plane from about 40 feet away, and then direct me to make very minute turns until the plane was lined up exactly along the magnetic direction being tested. We calibrated both the Sandel 3308 and the PAI 700. The Sandel calibration screen is pretty cool -- you just select the appropriate direction and then turn the heading bug knob until the exact corresponding direction is displayed. The display would show the amount of error (ie: N +8.3, S -2.1, etc.). The PAI has two adjustment screws -- one for N/S, and the other for E/W. According to the avionics guy, the idea is to balance the errors across the opposing directions. Anyway, after doing the 4 directions, we then did the cardinal points (eg: 30, 60, 120, 150, 210, 240, 300, 330), and measured the difference between the Sandel's direction and that of the PAI. After doing this on the ground, we then took a flight and discovered that the differences on the ground were sometimes significantly different than those in the air. Very strange. Sometimes the differences were as much as 5 degrees. I would dial in 30 degrees on the heading bug; the auto-pilot would fly that heading exactly (although the ground track would be different because of cross-winds), and the PAI card-compass would read differences that were different from the ones we measured on the ground. I'm still thinking it through: I don't think it was any of the usual magnetic errors (turning, acceleration or deceleration), because we were flying at a constant rate and at a constant altitude (level). Maybe some of you "old hands" have experienced or understand this and can give me a clue? -- Best regards, Alan K. Stebbens , N4184R, PA32-300, SBA