The yellow mark on an aircraft tube usually indicates the_______ point.

• A. Light
• B. Center
• C. Heavy
• D. End

Answer: (C)

The main idea is about orientation and balance of a tube in an aircraft. A yellow mark is used as a quick visual cue to identify which end of the tube is the heavier one. Knowing which end is heavier helps technicians install and align the tube consistently, ensuring proper balance and preventing vibration or misalignment in the system. The heavier end is the reference point for orientation, so marking it aids in correct installation across assemblies, brackets, and fittings.

Choosing a mark for a light end wouldn’t provide the needed balancing reference, and marks for the center or the far end don’t convey information about mass distribution. So the yellow mark is specifically used to indicate the heavy end.