ASI calibration Q
I have just had my ASI checked and at 140kt indicated (TB20) it was reported as reading 5kt high.
This doesn't seem right, relative to fuel flow and previous performance over the 5 years I've had the plane.
Today I flew the GPS cal method, where you fly at 120 deg apart headings, 3 legs, and plug the ground speeds into a formula, and the error is about 1kt.
I suppose my Q is how does the standard ASI calibrator work? It is just a pipe which fits over the pitot tube, and uses static pressure only. How can it be accurate? The GPS method is definitely accurate, yet its result is 4kt (~ 3%) different.