Air Data Inertial Reference Unit (ADIRU) alignment should not be attempted at latitudes greater than ______.

• A. 78°15'
• B. 76°00'
• C. 80°00'
• D. 72°30'

Answer: (A)

ADIRU alignment relies on gravity to establish the attitude reference and on the rotation of the Earth to help fix heading. At latitudes above 78 degrees 15 minutes, the geometry near the poles makes the gravity vector’s horizontal component very small and the yaw reference less reliable, so the alignment process may fail to converge or produce large errors. To protect navigation integrity, alignment should not be attempted when you’re past 78°15'.