Which item is NOT among the five loads acting on main engine bearings?

• A. Weight of the Rotating Mass
• B. Axial Forces From Power Changes and Thrust Loadings
• C. Vibration From the Air Stream, the Aircraft, and the Engine
• D. Oil Pressure Fluctuations in the Lubrication System

Answer: (D)

The thing being tested is what kinds of forces bearings actually have to support. Main engine bearings carry forces that come from the engine’s rotating parts and its operating environment: the rotating mass adds a static radial load, changes in power and thrust create axial forces along the shaft, and vibrations from the air flow, the aircraft, and the engine itself produce dynamic loads on the bearings. Oil pressure fluctuations in the lubrication system don’t constitute a bearing load in the same sense; they affect lubrication quality and film thickness, influencing wear and heat, but they aren’t a separate external force the bearing must resist.