After an aircraft engine has been shut down for more than 30 minutes, the propeller should be rotated to check for hydraulic lock. How many revolutions are recommended?

After an aircraft engine has been shut down for more than 30 minutes, the propeller should be rotated to check for hydraulic lock. How many revolutions are recommended?

• A. Rotate through at least 2 revolutions
• B. Rotate 1 revolution
• C. Rotate 0 revolutions
• D. Rotate 5 revolutions

Answer: (A)

Rotating the propeller after a long shutdown checks for hydraulic lock in the propeller pitch/hydraulic drive system. When oil or fluid settles, a lock can form that resists initial movement. Turning the propeller through multiple turns—at least two full revolutions—helps break any such lock and confirms the system will rotate smoothly as oil is distributed and the mechanism bleeds. If you feel abnormal binding or heavy resistance after these turns, stop and inspect the hydraulic circuit and propeller hub for issues.

Rotating the propeller after a long shutdown checks for hydraulic lock in the propeller pitch/hydraulic drive system. When oil or fluid settles, a lock can form that resists initial movement. Turning the propeller through multiple turns—at least two full revolutions—helps break any such lock and confirms the system will rotate smoothly as oil is distributed and the mechanism bleeds. If you feel abnormal binding or heavy resistance after these turns, stop and inspect the hydraulic circuit and propeller hub for issues.