Definition
The total error that builds up in an instrument or measurement system as a series of small individual errors add together over time or across successive readings. Each small inaccuracy on its own may be insignificant, but combined they produce a meaningful deviation from the true value.
Plain English
Lots of tiny errors stacking up until the total becomes large enough to matter.
Context Anchor
Seen in navigation, flight planning, instrument accuracy, and position estimates, especially when a pilot is using heading, speed, time, and wind information to estimate where the aircraft is.
Derivation
From the Latin 'accumulare', meaning 'to heap up' or 'to pile together'. The word captures the idea that the error is not a single mistake but a build-up of many smaller ones.
Why Pilots Care
Unchecked accumulated error can cause significant position inaccuracies, leading to navigation deviations or missed waypoints.
Analogy
Similar to how small rounding errors in repeated calculations can produce a large final discrepancy.
Intuition Check
Do not think of accumulated error as one single big mistake. It usually means several small differences that build up into a larger difference.
Example Sentence 1
After an hour of flight, the heading indicator showed several degrees of accumulated error and had to be reset against the magnetic compass.
Example Sentence 2
Inertial navigation units require periodic updates to reset accumulated error from sensor drift.