What should pilots do first after detecting GNSS failure?

What should pilots do first after detecting GNSS failure?

• A. Cross-check navigation sources
• B. Contact ATC immediately
• C. Declare an emergency
• D. Switch to VOR flight plan

Answer: (A)

The main idea is to quickly establish what navigation data you can still trust when GNSS fails. The first step is to cross-check navigation sources. By comparing GNSS indications with independent means (such as VOR/LOC receivers, DME, and the inertial or standby navigation instruments), you confirm whether the loss is GNSS-only and identify which non-GNSS aids are still usable. This preserves situational awareness and tells you how you can safely proceed: you can re-establish your route and altitude using available non-GNSS navigation, rather than assuming the GNSS fault means immediate emergency or switching to a single backup plan without verification. After this cross-check, you can decide on the next steps—such as reprogramming the flight plan to use VOR-based navigation if appropriate, coordinating with ATC, or declaring an emergency only if safety requires it.

The main idea is to quickly establish what navigation data you can still trust when GNSS fails. The first step is to cross-check navigation sources. By comparing GNSS indications with independent means (such as VOR/LOC receivers, DME, and the inertial or standby navigation instruments), you confirm whether the loss is GNSS-only and identify which non-GNSS aids are still usable. This preserves situational awareness and tells you how you can safely proceed: you can re-establish your route and altitude using available non-GNSS navigation, rather than assuming the GNSS fault means immediate emergency or switching to a single backup plan without verification. After this cross-check, you can decide on the next steps—such as reprogramming the flight plan to use VOR-based navigation if appropriate, coordinating with ATC, or declaring an emergency only if safety requires it.