Hi,

1) There is a switch to toggle between [DOPPLER] and [INS] navigation system. It is located at Left Forward Panel below the clock (see Flight Manual Part II – Aircraft and Systems pages 8, 22, 40 and 50..

By default, it is [DOPPLER]. Did you toggle it to [INS] before go to [AP] > [NAV]?

[DOPPLER]
- Autopilot in NAV mode tracks Doppler Navigation System
- Heading Bug on Captain's HSI controlled by HSI Heading Selector

[INS]
- Autopilot in NAV mode tracks CIVA INS
- Heading Bug on Captain's HSI controlled by CIVA INS

2) Check if [CIVA-INS Control Panel] at Overhead Panel is turned to [NAV] and the Ready Nav Green Light is ON.

Hope this help,

Pinatubo.