Definition
A self-contained navigation method that determines an aircraft's position, velocity, and attitude by continuously measuring its accelerations and rotations from a known starting point, using onboard accelerometers and gyroscopes. It does not rely on any external signals such as ground stations or satellites.
Plain English
A way of knowing where the aircraft is by starting from a known point and tracking every movement and turn it makes from that point onward, using only equipment inside the aircraft.
Context Anchor
Seen in instrument procedures and area navigation discussions, especially when a procedure or system description refers to navigation based on onboard equipment.
Derivation
From the Latin 'iners,' meaning inactive or resistant to motion. 'Inertia' is the property that makes a body resist changes in its motion. Inertial navigation works by sensing those resistance forces (accelerations) directly, which is why it needs no outside reference.
Why Pilots Care
Delivers continuous position data when external references are unavailable, supporting accurate departures and flight in remote or signal-denied areas.
Analogy
It is like starting at a known spot on a ramp, then keeping a careful running count of every turn, speed change, and distance traveled to work out where you are now.
Intuition Check
Do not assume inertial navigation means satellite navigation. Inertial navigation can estimate position by sensing the aircraft’s own movement from a known starting point.
Example Sentence 1
On long oceanic legs, the crew relied on inertial navigation because no ground-based navigation aids were within range.
Example Sentence 2
During the climb, the inertial navigation unit provided position updates when GPS signals were briefly lost.