The regulations require transport aircraft to be designed to meet specified acceleration and gust limits and require maximum design speeds (V_NE, V_NO, M_MO, V_MO, etc.) to be defined so that any upset that occurs does not lead to acceleration to a point where the aircraft's structure fails.

These speed limitations are normally set to prevent them from suffering structural damage due to high air loads and to avoid handling difficulties created by the trim changes they sometimes create at higher speeds.

A manoeuvre load diagram displays the load factor limitations and speed limitations together and indicates the combinations of these where we can fly.

The "g" limits laid down by the regulations in CS 25 are +2.5g and -1g at maximum design mass for transport aircraft flying with flaps up. Sometimes these are also referred to as the "Limit Load Factor".

Exceeding these limits might cause some permanent deformation of the airframe.

With the term "design" we mean the figures used during the design process and the aircraft has to meet those design requirements. Once the aircraft is released for operation, flight manuals use authorised figures, which may be equal to but do not exceed the "design" figures.