The invention relates to a seat, in particular air passenger seat, with seat components, such as a seat part (10) and a backrest (12) with a housing shell (20), which is part of the backrest (12) or which at least partially includes the backrest (12) at the back and which comprises at least two shell parts which are connected to each other, at least in an initial state, via a fixing device and of which the one shell part is moved under a sudden introduction of force, such as, for example, in the event of a crash, relative to the other shell part in such a manner that an engagement space between the shell parts is opened up. This provides a solution in which, in the event of a crash, body parts of the seat user, such as his head, can still impact against shell parts in the backrest region of the seat but a shell part affected to this extent continues to move, without a relatively large amount of resistance, in relation to the other shell part in each case, which is arranged in a stationary manner, in a direction which permits an engagement space to be opened up.