Which items are included in the Basic Empty Mass (BEM) of an aircraft?

The Basic Empty Mass (BEM) of an aircraft is defined as the mass of the aircraft including all standard equipment and systems, but without any payload or usable fuel. This definition typically encompasses the airframe, the basic equipment necessary for the aircraft to operate, and a certain amount of unusable fuel. It is important because it provides a baseline measurement for determining the total mass of the aircraft when considering loading operations.

Considering the other options, the first choice mistakenly suggests that the BEM includes only the mass of the airframe. While the airframe is a component of the BEM, it does not encompass all necessary items that contribute to the BEM definition. The third choice inaccurately adds payload and usable fuel into the calculation, which contradicts the fundamental definition of BEM as it should not include these variables. The final option focuses solely on the weight of the pilot and crew, which is also not part of the BEM since it is calculated separate from any operational load factors. Therefore, the correct understanding aligns with the choice that incorporates the basic equipment and unusable fuel, which are fundamental elements of the aircraft's BEM.