FAA Powerplant Written Practice Test

How should aircraft engine spark plugs be installed?

1. Hand tight without a tool

2. Finger tight and then torqued

3. Inspected before installation

4. Installed with permanent thread lock

The correct answer is: Finger tight and then torqued

The proper installation of aircraft engine spark plugs involves a process that ensures their secure and effective operation while also preventing damage to the engine. When spark plugs are installed finger tight and then torqued, it allows for the correct amount of compression within the cylinder head without over-tightening, which could lead to damage to the threads or failure of the spark plug. Finger tightening provides a preliminary secure position for the spark plug, allowing it to seat appropriately within its threaded hole. Following this, using a torque wrench ensures that the spark plug is tightened to the manufacturer's specified torque setting. This step is crucial because each spark plug type may have different torque requirements, and achieving the correct torque avoids potential issues such as spark plug loosening during engine operation or insufficient sealing against combustion gases. The choice of inspecting the spark plugs before installation is indeed important for ensuring their functionality, but it comes after the installation technique in terms of securing the proper operation. Hand-tightening without a tool does not provide an accurate level of tightness, and using permanent thread lock could lead to complications and make future removal of the spark plugs difficult or impossible.