Definition
Any unexpected loss, degradation, or unreliable behavior of the Global Positioning System signal or position output during flight. This includes loss of navigation capability, loss of integrity monitoring (such as RAIM), erroneous position information, or interference (intentional jamming or unintentional). Pilots operating under IFR are required to report GPS anomalies to ATC.
Plain English
When your GPS isn't working the way it should — it loses signal, gives a wrong position, or warns you it can't be trusted — that's a GPS anomaly, and ATC needs to know.
Context Anchor
Pilots encounter this term in reports about GPS signal problems, especially when using GPS for navigation or for an instrument approach.
Derivation
Anomaly comes from the Greek 'anomalos,' meaning 'uneven' or 'irregular.' In aviation it's used for any deviation from normal, expected behavior — here, the GPS doing something other than working correctly.
Why Pilots Care
A GPS anomaly can invalidate a GPS approach or enroute guidance, requiring immediate switch to an alternate navigation source.
Intuition Check
Do not assume a GPS anomaly always means the entire GPS system has failed. It can be any abnormal GPS behavior, from a brief loss of signal to guidance that does not match the aircraft’s actual position.
Example Sentence 1
After the GPS flagged a loss of integrity over the desert, the pilot reported the GPS anomaly to Center and requested vectors.
Example Sentence 2
ATC broadcast a GPS anomaly alert due to interference, so the crew cross-checked position with ground-based aids.