Compare Global Navigation Satellite System (GNSS) position determination with Inertial Navigation System (INS) position estimation, including their inputs and a limitation of each.

### Why this is right The key contrast is the source of position information. GNSS measures distances to satellites, while INS measures the aircraft’s own acceleration and rotation. Their limitations follow from those mechanisms: GNSS needs satellite signals, and INS accumulates sensor error over time. ### The concept GNSS receivers use satellite signals to estimate distance and combine those measurements through trilateration. An aeronautical database helps the system relate coordinates to waypoints and other navigation data. INS begins from a known aligned position and integrates measurements from gyroscopes and accelerometers to estimate movement. It does not need ground aids or satellite signals, but small sensor errors accumulate as the flight continues. These systems therefore use different inputs and have different failure or accuracy considerations. ### What a good answer covers - GNSS uses satellite signals and distance-based trilateration. - INS uses onboard acceleration and rotation sensors. - INS starts from a known aligned position and does not need external navigation signals. - INS accuracy reduces over time as sensor errors accumulate. ### Terms - **Global Navigation Satellite System (GNSS)**: satellite-based navigation using signals from satellite constellations. - **Inertial Navigation System (INS)**: onboard navigation based on measured aircraft motion. - **Trilateration**: calculating position from distances to known points. - **Aeronautical Information Regulation and Control (AIRAC)**: the aeronautical database information cycle and database referred to in the material. ### Remember GNSS measures distance to satellites; INS estimates movement from onboard sensors.