To provide for the above operational modes used in flight, there are three methods of GRU alignment as follows:

a. Selecting the MAN/STORE/MAG switch on the gyro controller to the MAN position provides GRU alignment to a heading manually selected on the MHIC panel. Prerequisite to such an alignment is the positioning of the helicopter’s longitudinal axis parallel to either a surveyed line or on a known heading.
b. Selection of the switch to STORE provides GRU alignment to a heading locked in the Compass Repeater Amplifier (CRA-3) at time of shut down and the aircraft has not been moved. This mode of alignment is normally used at remote airfields where surveyed lines are not available.
c. When selected to MAG, GRU alignment is provided to true or grid north using magnetic heading information from the flux valve, modified by the variation/grivation angle, as set by the INCR/DECR push-button on the controller. In the absence of surveyed lines, shore based originating fights normally
perform MAG GRU alignments.

It is important to stress that navigation cross track error is dependent on the accuracy with which the GRU can be referenced to true north. Attainable accuracies are given as follows:

a. MAN. 30 arc minutes.
b. STORE. 30 arc minutes + accumulated gyro drift.
c. MAG. 2 degrees.