Inertial Navigation System (INS) is a navigation technology and an electronic system that uses motion sensors - accelerometers and gyroscopes - to calculate an object's position and orientation without external reference. Traditionally a self-contained navigation device, INS relies on a gyro-stabilised platform for dead-reckoning, continuously incorporating sensed accelerations and rotations to track trajectory. The pilot interface allows a limited number of waypoints to be entered, while basic navigation information is displayed in the cockpit.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is INS in aviation?
An Inertial Navigation System (INS) is a self-contained navigation aid that continuously calculates position, orientation, and velocity by dead reckoning without external references. An inertial navigation system (INS) uses motion sensors like accelerometers, rotation sensors like gyroscopes, and a variety of environmental sensors. The system comprises an Inertial Measurement Unit (IMU) containing gyroscopes and accelerometers, a GNSS receiver, and sensor fusion software. After initialization, which establishes the relationship between the aircraft frame and the geographic reference, the INS processes raw outputs from the IMU to determine the aircraft's velocity, orientation, and position relative to a known starting point. By incorporating information from motion sensors, it provides roll, pitch, heading, position, and velocity data to flight crews, enabling accurate route planning and guidance during long flights over areas without ground-based navigation aids.
What is the difference between an INS and IRS in aviation?
The difference between an INS and IRS is that an Inertial Navigation System (INS) is a self-contained navigation device that continuously calculates position, velocity and orientation by dead-reckoning. Starting from an initial known position and velocity it uses motion sensors - accelerometers to measure linear acceleration and gyroscopes to measure rotation - then integrates these data with a computer. The traditional INS employs gimballed gyroscopes and provides higher-rate position updates to the autopilot. It adds the ability to catalogue various positions as waypoints for waypoint navigation. It is more accurate than a satellite navigation receiver, yet it still demands an initialisation process while the aircraft is stationary to establish the relationship between the aircraft frame and the geographic reference, and it performs better when subsequently provided with some data inputs.
The Inertial Reference System (IRS) is a solid-state unit that expands upon the capabilities of the INS. It is built around three Ring Laser Gyros coupled with quartz accelerometers that detect linear and angular acceleration in three dimensions, and it performs the same calculations to deliver airplane position, ground speed, vertical speed, acceleration, track, true heading, magnetic heading and wind speed and direction. The IRS is therefore the main navigational system in modern aircraft: it supplies attitude data for displays, the flight management system, flight controls, engine controls, the artificial horizon and the yaw damper. The IRS Mode Control Panel on the overhead panel controls the system; rotating the selector from OFF to NAV begins a short power test followed by alignment, a process that again requires the aircraft to remain stationary while the unit measures the rotation of the Earth. Unlike GNSS, the IRS is a self-sufficient system that needs no outside input to know where it is on the Earth, providing a fall-back when GNSS fails.
