Definition
Unexpected degradations, interruptions, or errors in GPS signal reception or position information that affect the accuracy, integrity, or availability of GPS-based navigation. Causes include satellite outages, ionospheric disturbances, intentional or unintentional radio frequency interference (including jamming and spoofing), terrain masking, and receiver faults. Anomalies may trigger a loss of Receiver Autonomous Integrity Monitoring (RAIM), a flag on the navigation display, or unreliable position data.
Plain English
Times when GPS stops working properly — giving wrong, missing, or unreliable position information instead of the accurate signal pilots rely on.
Context Anchor
Seen in instrument flying when a GPS receiver gives a warning, loses guidance, shows unexpected position changes, or when pilots are told GPS service may be unreliable in an area.
Derivation
Anomaly comes from the Greek 'anomalia,' meaning irregularity or deviation from the norm. In aviation, it signals that something is behaving outside expected operation — useful framing because GPS anomalies are not failures of the equipment so much as departures from normal signal behavior.
Why Pilots Care
GPS anomalies can lead to navigation errors, requiring pilots to switch immediately to backup methods such as ground-based navigation aids to maintain safe flight.
Grounding Statement
A GPS anomaly can be as simple as the airplane symbol jumping to the wrong place on the display or the receiver warning that GPS guidance is no longer dependable.
Intuition Check
Do not assume a GPS anomaly is just a harmless screen glitch. In aviation, it means the GPS information may be unsafe to rely on until it is confirmed reliable again.
Example Sentence 1
After receiving a GPS anomaly alert, the pilot reverted to VOR navigation and advised ATC.
Example Sentence 2
During the approach the crew noticed GPS anomalies and verified their position using other cockpit instruments.