Which statement about the accelerometers in an INS is accurate?

• A. Three accelerometers measure acceleration in pitch, roll, and yaw
• B. One accelerometer measures altitude
• C. All accelerometers are mounted unsecured
• D. The accelerometers measure only velocity

Answer: (A)

In an INS you rely on a triad of accelerometers, each aligned with one body axis, to sense linear acceleration along three mutually perpendicular directions. This three-axis arrangement lets the system resolve motion in 3D and provides the gravity reference used for estimating the vehicle’s attitude and velocity. While pitch and roll are directly tied to how gravity is oriented relative to the aircraft, yaw is an angular rotation about the vertical axis that is typically measured by gyroscopes; accelerometers contribute the linear acceleration components along each axis and are used together with gyro data to maintain full orientation and position estimates. The other statements don’t fit because altitude isn’t measured by a single accelerometer, accelerometers are securely mounted to the frame (not unsecured), and they measure acceleration—not velocity.