What factor is used to assign aircraft to a category?

The correct factor used to assign aircraft to a category is maximum takeoff weight. This parameter is essential because it directly impacts the aircraft's performance capabilities, such as its takeoff, climb, and landing characteristics. Categories are often based on weight classes because this influences regulatory requirements, operational limitations, and the types of procedures that need to be followed.

Maneuvering speed, while important for pilot awareness and maintaining control, is not a primary determinant for category assignment. It relates more to the aircraft's handling characteristics within a given weight configuration rather than defining a broad category to which the aircraft belongs.

Landing speed and normal cruise speed are also significant for operational performance but do not serve as the standard basis for categorizing aircraft under regulations. These speeds can change based on weight and configuration, making them less suitable as definitive categorization criteria. Thus, maximum takeoff weight remains the principal factor in the classification of aircraft into various categories.