Definition
A self-contained navigation system that determines an aircraft's position, velocity, and attitude by continuously measuring its own accelerations and rotations using internal sensors (accelerometers and gyroscopes), starting from a known initial position. It requires no external signals such as radio aids, GPS, or ground stations to operate.
Plain English
A navigation system that tracks where the aircraft is by sensing every movement it makes from a known starting point. It works entirely on its own, with no help from outside signals.
Context Anchor
Seen in autopilot and navigation discussions, where the aircraft’s guidance equipment needs reliable information about position and movement.
Derivation
From Latin 'inertia,' meaning 'inactivity' or 'resistance to change in motion.' The system measures the aircraft's resistance to changes in motion (its accelerations and rotations) to figure out where it has moved. The name reflects that the system relies entirely on the physics of motion itself, not on outside references.
Why Pilots Care
Enables accurate navigation and autopilot guidance over oceans or remote areas where GPS or ground stations cannot be used.
Analogy
It is like starting at a known spot on a map and then keeping track of every step, turn, and change in speed to estimate where you are now.
Intuition Check
Do not assume inertial navigation systems are the same as satellite navigation. They work by sensing the aircraft’s own movement from a known starting point.
Example Sentence 1
After losing GPS reception over the ocean, the crew continued navigating using the aircraft's inertial navigation system.
Example Sentence 2
Before departure the crew aligned the inertial navigation system to the aircraft's exact ramp position.