What type of navigation aids are primarily used under IFR?

The primary navigation aids used under Instrument Flight Rules (IFR) are radio aids such as VORs (VHF Omnidirectional Range), NDBs (Non-Directional Beacons), and modern GPS systems. These aids provide pilots with reliable reference points for navigation while flying in conditions where visual references might be obscured, such as in clouds, fog, or darkness. VORs and NDBs offer ground-based navigation capabilities, while GPS enhances navigational precision with satellite technology, offering a wider range of course guidance, waypoints, and real-time positional information.

This reliance on these specific types of navigation aids ensures pilots can maintain situational awareness and safely navigate during instrument flight, adhering to the stringent requirements of IFR operations. Other options do not provide the systematic and continuous navigational support required for IFR flying, reflecting the unique aspects of flying in both controlled and uncontrolled airspaces that IFR pilots must master.