Which of the following is not a factor contributing to errors in an inertial navigation system?

Which of the following is not a factor contributing to errors in an inertial navigation system?

• A. Apparent drift
• B. Computer errors
• C. Leveling gyro drift
• D. Initial azimuth misalignment

Answer: (A)

The main idea is how errors accumulate in an inertial navigation system. An INS relies on integrating angular rates from gyros and accelerations from accelerometers to compute attitude, velocity, and position. Real-world factors that create those errors include gyro bias and drift, misalignment of the sensor axes, and errors introduced by the processing computer (finite precision and rounding). Apparent drift isn’t a separate, intrinsic error mechanism in the INS error model. The drift you observe is the result of real error sources such as gyro bias, misalignment, or processing limitations, not a distinct factor itself. That’s why it isn’t treated as a separate contributor. Leveling gyro drift and initial azimuth misalignment are definite sources of error. Drift in a leveling gyro affects the reference frame used for attitude, causing attitude and thus position errors to grow over time. An incorrect initial azimuth means the starting orientation is off, and since the INS continuously integrates from that point, the heading error persists and compounds. Computer errors, arising from finite word length and arithmetic rounding, also contribute, albeit usually smaller, errors that propagate through the navigation solution. So the factor that isn’t a separate contributor is apparent drift, while the others are established sources of INS error.

The main idea is how errors accumulate in an inertial navigation system. An INS relies on integrating angular rates from gyros and accelerations from accelerometers to compute attitude, velocity, and position. Real-world factors that create those errors include gyro bias and drift, misalignment of the sensor axes, and errors introduced by the processing computer (finite precision and rounding).

Apparent drift isn’t a separate, intrinsic error mechanism in the INS error model. The drift you observe is the result of real error sources such as gyro bias, misalignment, or processing limitations, not a distinct factor itself. That’s why it isn’t treated as a separate contributor.

Leveling gyro drift and initial azimuth misalignment are definite sources of error. Drift in a leveling gyro affects the reference frame used for attitude, causing attitude and thus position errors to grow over time. An incorrect initial azimuth means the starting orientation is off, and since the INS continuously integrates from that point, the heading error persists and compounds.

Computer errors, arising from finite word length and arithmetic rounding, also contribute, albeit usually smaller, errors that propagate through the navigation solution.

So the factor that isn’t a separate contributor is apparent drift, while the others are established sources of INS error.