Definition
A value calculated by a GPS or other navigation receiver that represents how far the displayed aircraft position may differ from the actual position. EPE is a real-time estimate of the receiver's own positional uncertainty, expressed in distance (typically feet, meters, or nautical miles), based on satellite geometry, signal quality, and the number of satellites being tracked.
Plain English
It is the navigation receiver's own best guess of how wrong it might be. If the box shows you in one place but admits the true position could be off by some amount, that admitted amount is the EPE.
Context Anchor
Seen in satellite-based navigation and other aircraft navigation system information, especially when checking whether the system’s position information is reliable enough to use.
Derivation
Plain English: 'estimated' means a calculated guess rather than a measured fact, and 'position error' means how far off the shown position might be from the real one. Together: the receiver's own guess at how wrong it could be right now.
Why Pilots Care
It shows whether the GPS position meets the accuracy needed for the current phase of flight or instrument approach.
Grounding Statement
A small EPE means the displayed position is expected to be close to the aircraft’s real position; a large EPE means there is more uncertainty.
Intuition Check
Estimated Position Error does not mean the pilot made a mistake. Here, error means the possible difference between the shown position and the aircraft’s true position.
Example Sentence 1
Before starting the approach, the pilot checked the GPS status page and confirmed the EPE was well within the limits required for the procedure.
Example Sentence 2
When the EPE exceeded the required limit the pilot discontinued the GPS-based arrival and switched to ground-based navigation.