Definition
The progressive loss of accuracy in an Inertial Navigation System's (INS) computed position over time, caused by the accumulation of small sensor errors that compound during flight. Because an INS calculates position by continuously integrating acceleration and rotation measurements from its initial alignment point, any tiny errors in those measurements grow steadily, producing a position output that drifts further from the aircraft's true position the longer the system runs without external correction.
Plain English
The longer an inertial navigation system runs, the further off its reported position drifts from where the aircraft actually is. The error grows slowly but steadily.
Context Anchor
Seen in instrument flying when discussing INS errors and how a navigation system’s position can drift if it is not updated or corrected.
Derivation
Degradation comes from the Latin 'gradus' meaning 'step,' with 'de-' meaning 'down.' So degradation is literally a 'stepping down' — a gradual decline. In this context, the position output steps down in quality over time.
Why Pilots Care
Unchecked position degradation can place the aircraft miles off course, requiring timely cross-checks with GPS, VOR, or other references.
Grounding Statement
Picture the aircraft in one place, while the navigation display slowly shows it a little farther away from that true place as errors build.
Intuition Check
Do not read degradation of position as the aircraft being in a worse physical location. Here it means the calculated position is becoming less accurate.
Example Sentence 1
After six hours of overwater flight, the crew noted the expected degradation of position in the INS and updated it against GPS at the next waypoint.
Example Sentence 2
The pilot cross-checked the INS against GPS to correct for degradation of position.