If a radial engine has been shut down for more than 30 minutes, what should be done with the propeller?

When a radial engine has been shut down for more than 30 minutes, it's important to rotate the propeller through at least two revolutions before attempting to start the engine again. This practice serves several critical purposes. First, it helps to ensure that oil is circulated throughout the engine's components. After a period of inactivity, oil can settle, leading to inadequate lubrication at startup, which may cause wear or damage.

Additionally, rotating the propeller helps to check the movement of the engine's internal components, making sure that nothing is stuck or jammed. By turning the propeller, the pilot or maintenance personnel can confirm that the engine is mechanically sound and ready for operation. This step is crucial for maintaining engine health and longevity.

The other options, while important in various circumstances, do not address the immediate need for ensuring that the engine is properly lubricated and operationally ready. Checking the fuel level, inspecting the ignition system, and draining excess oil may be necessary tasks in the broader context of engine maintenance, but they do not specifically relate to the action needed after a shutdown of over 30 minutes.