The CDI can be toggled between ground-based NAVAID and what other system?

• A. Ground-based NAVAID
• B. FMS
• C. GPS
• D. INS

Answer: (B)

The main idea here is that the CDI can source its steering guidance from two broad navigation systems: conventional ground-based NAVAIDs and the flight management system. The correct choice points to the FMS because, apart from VOR/LOC signals, modern cockpits can drive the CDI from the flight management system’s RNAV guidance, which follows the programmed flight plan rather than a ground beacon. This lets you fly routes generated by the FMS (often using GPS as the underlying position source) instead of just tracking a VOR or localizer signal. The other options represent possible sources the CDI might interface with in some setups, but the question specifically asks for the system that provides RNAV guidance beyond ground-based NAVAIDs, which is the flight management system.