Just Flight Standard VC10 Operation Manual page 80

To improve our navigational accuracy, we will use the INS in 'Aided Inertial Operation' mode. With the MSU
mode selectors set to NAV and the API value below 4, we can now configure this. Confirm that the CDU mode
selectors are set to DSRTK/STS and then press the 4 key on the CDU keypad. The right-hand display will show
a series of '0' digits followed by a '4', and the INSERT button will illuminate.
Press the INSERT button on both CDUs.
VC10 Professional – Operations Manual
80