FAA AMT (Aviation Maintenance Technician) Airframe Practice Exam

The fixed line mark attached to the compass bowl of a magnetic compass is called the "Lubber Line." The Lubber Line is a reference mark on the compass bowl that remains fixed and is used to indicate the aircraft's current heading. It provides a visual reference point for the pilot or navigator to read the heading indicated by the compass. The other options are incorrect because:

A. Heading Indicator: A heading indicator is an instrument that uses a gyroscope to provide heading information based on the principle of rigidity in space. It is not a fixed line mark on the compass bowl.

B. Directional Gyro: A directional gyro is an instrument that indicates the aircraft's heading based on a gyroscope. It is not the fixed line mark on the compass bowl.

D. Bezel Ring: The bezel ring is the outer ring on a compass that can be rotated to set the desired heading. It is not the fixed line mark on the compass bowl.