acceleration error

i. An error in magnetic compasses caused by acceleration forces acting on the dip-compensating weight when an aircraft is flying in an east-west direction. In the Northern Hemisphere, when the aircraft accelerates in an east-west direction the compass indicates the aircraft is turning north; it indicates south when decelerating on these headings. The error occurs because the magnet is being pivoted and the point of the pivot and the center of gravity are not coinciding. The errors are in the opposite direction if the compass is correctly decompensated for operations in the Southern Hemisphere.

Aircraft accelerates from 180 knots to 210 knots when on course of 090°. The magnetic compass, however, shows as if aircraft has turned from 090 to 120°. Similarly, when aircraft decelerates from 180 knots to 160 knots in a straight and level flight, the compass shows a turn to the left—in this case to 060°. In both cases, compass comes back to the original course as soon as the acceleration/deceleration has stopped.

Note: These changes are for the Northern Hemisphere. The changes will be reversed if the aircraft is operating in the Southern Hemisphere and if the compass has been correctly dip-compensated for the Southern Hemisphere.

ii. An error in a bubble sextant caused by mechanical inertia during changes in an aircraft’s velocity.