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What’s New: A recent new UK warning for aircraft about GNSS interference. It also lists some of the systems that can fail when GPS/GNSS is not available.

Why It’s Important:

  • Pilots need to stay on their toes in such situations. Always good to remind them of the dangers and to avoid becoming complacent.
  • The areas of concern are increasing in number and size. Note the Arctic is included.
  • From the advisory – “ is not possible to predict outages and their effects.” and “,,,in certain cases leading to re-routing or diversion due to the inability to perform a safe landing procedure.”

What Else to Know: From the advisory:

The following non-exhaustive list includes some potential issues that a degradation of GNSS signal could generate:

  • Loss of ability to use GNSS for waypoint navigation;
  • Loss of area navigation (RNAV) approach capability;
  • Inability to conduct or maintain Required Navigation Performance (RNP) operations, including RNP and RNP Authorization Required (RNP(AR)) approaches;
  • Triggering of terrain warnings, possibly with pull up commands;
  • Inconsistent aircraft position on the navigation display;
  • Lost automatic dependent surveillance-broadcast (ADS-B), wind shear, terrain and surface functionalities;
  • Failure or degradation of ATM/ANS/CNS [Air Traffic Management/Air Navigation System/Communications and Navigation System] and aircraft systems which use GNSS as a time reference;
  • Inaccurate TCAS [Traffic Alert and Collision Avoidance System] traffic information on navigational displays;
  • Potential airspace infringements and/or route deviations due to GNSS degradation.


Thanks to John Pottle and the Royal Institute of Navigation for highlighting this to us!


Civil Aviation Authority SAFETY NOTICE Number: SN–2023/001
Version 2 Issued: 15 April 2024

Global Navigation Satellite System Outage Leading to Navigation/Surveillance Degradation

This Safety Notice contains recommendations regarding operational safety.
Recipients must ensure that this Notice is copied to all members of their staff who need to take appropriate action or who may have an interest in the information (including any ‘in-house’ or contracted maintenance organisations and relevant outside contractors).