When must ATS be advised regarding deterioration of GNSS navigation capability?

• A. When GNSS receiver is in dead-reckoning mode, or experiences loss of its navigation function, for more than one minute
• B. Immediately on any degradation
• C. Only after landing
• D. After fuel is exhausted

Answer: (A)

When navigation capability deteriorates, ATC needs to know so they can manage traffic safely and arrange appropriate contingencies. If the GNSS receiver is in dead-reckoning mode or has lost its navigation function for more than a minute, the aircraft is operating with degraded position accuracy, which can affect separation, routing, and contingency planning. Not every brief glitch requires ATS notification, since short degradations may resolve quickly and pose little immediate risk, but a loss or transition to dead-reckoning lasting over a minute represents a significant change in navigation reliability that ATC should be aware of. This isn’t about after landing or after fuel runs out; those moments are outside the active en-route or approach phase where ATS coordination for navigation integrity is relevant.