Which navigation aid is commonly used as a backup when GNSS is unavailable?

Which navigation aid is commonly used as a backup when GNSS is unavailable?

• A. VOR
• B. ILS
• C. DME
• D. ADF

Answer: (A)

When GNSS is unavailable, pilots rely on ground-based radio navigation that does not depend on satellites. VOR provides azimuth information from a fixed station, allowing you to determine your bearing relative to that station and, when combined with DME, your distance to it. This combination lets you navigate enroute and fly procedures without GPS, and it’s widely deployed and well understood in the cockpit. ILS is designed for precise approach to a specific runway and isn’t a general backup for navigation in the enroute or non-precision segments. DME by itself gives distance but no bearing, so it must be paired with a VOR or ILS for meaningful navigation. ADF/NDB systems exist but are older, less accurate, and being phased out in many areas. That makes VOR the most practical and commonly used backup when GNSS is down.

When GNSS is unavailable, pilots rely on ground-based radio navigation that does not depend on satellites. VOR provides azimuth information from a fixed station, allowing you to determine your bearing relative to that station and, when combined with DME, your distance to it. This combination lets you navigate enroute and fly procedures without GPS, and it’s widely deployed and well understood in the cockpit.

ILS is designed for precise approach to a specific runway and isn’t a general backup for navigation in the enroute or non-precision segments. DME by itself gives distance but no bearing, so it must be paired with a VOR or ILS for meaningful navigation. ADF/NDB systems exist but are older, less accurate, and being phased out in many areas. That makes VOR the most practical and commonly used backup when GNSS is down.