How does IRS alignment work and what affects alignment time?

IRS (Inertial Reference System) alignment determines initial position and establishes the navigation reference frame. Process: Aircraft must be stationary, Accelerometers measure Earth's gravity vector, Gyros measure Earth rotation rate, Position is entered manually or via GPS. These allow computation of local vertical and true north. Alignment time depends on: Latitude (longer near equator where Earth rotation rate horizontal component is zero), Required accuracy, Sensor quality, and Temperature stability. Typical alignment takes 5-15 minutes. Fast alignment modes using GPS can reduce time. Alignment errors become navigation errors; accuracy of 0.1 deg heading is typical. In-flight alignment is possible with GPS aiding.