area of uncertainty

area of uncertainty

The area around the DR (dead reckoning) position within which, for a stated level of probability, the true position is considered to occur. Normally, the 50% level of probability is taken. The area of uncertainty is drawn as a rectangle centered around the GPI (ground position indicator) DR position whose sides are equal to 1% along the track and 3% across the track of the distance flown since resetting the GPI. In the case of air-plot DR position, it is a circle of radius of 8 NM/h for aircraft at TAS (true air speed) up to 250 knots and 20 NM/h at higher speeds.