Where do you find a list of the lubricants that are approved for use in a constant-speed propeller?

• A. In the maintenance manual for the engine.
• B. In the aircraft owner's manual.
• C. In the maintenance manual for the propeller.
• D. In the FAA maintenance circular.

Answer: (C)

The list of lubricants approved for a constant-speed propeller is found in the propeller’s maintenance manual because that manual covers the propeller’s own lubrication system, seals, and operating requirements. It specifies which lubricants and viscosities are compatible with that specific propeller model, along with any maintenance notes or limits. Using an unapproved lubricant can cause improper seal compatibility, seal swelling, or incorrect acting of the pitch mechanism, which can affect performance and safety.

The engine maintenance manual deals with engine lubrication, not the propeller’s hydraulic and lubrication system. The aircraft owner’s manual is too general for system-specific approvals. A FAA maintenance circular provides regulatory information, not the model-specific lubricant approvals for a particular propeller.