The propeller is one of the least understood components on an aircraft especially among operators who may have mixed fleet types to include jet engine power passenger aircraft and smaller propeller driven aircraft whether they be gas turbine or piston engine powered. This module begins with a detailed explanation of a propeller blade and how it performs its designed function. Blade element theory, blade angles and rotational speeds, propeller slip, various forces acting on a propeller, torque and vibration are essential knowledge points. Propeller construction, pitch control systems, synchronizing and ice protection fill in the essentials. The special requirements of propeller maintenance and repairs as well as storage and preservation principles are also covered.