What inspection must be accomplished during a 100-hour inspection?

During a 100-hour inspection, checking cylinder compression is an essential part of the maintenance process. This inspection plays a crucial role in assessing the engine's performance and overall health. Cylinder compression indicates how well the engine is generating power; low compression values can signal potential issues such as worn piston rings, valve problems, or gasket leaks. By measuring the cylinder compression, maintenance personnel can ensure that the engine is operating efficiently and can identify any necessary repairs before they lead to more serious complications.

The other options involve important inspections, but they do not specifically fall under the core requirements of a 100-hour inspection as defined by aviation maintenance guidelines. While checking engine oil levels and inspecting fuel lines are vital for aircraft safety and function, they are part of standard pre-flight checks and other regular maintenance protocols rather than being exclusive to the 100-hour timeframe. Testing propeller pitch, although important, is not a specified task within the context of a 100-hour inspection, making the compression check the most pertinent choice.