An aircraft passenger seat assembly and backrest unit attachable to a seat assembly, the backrest being pivotally attached or fixed, and the backrest unit including at least one frame member having adjacent weakened and intact sections provided along a peripheral edge, the weakened section having a first failure load and the intact section having a second failure load greater than the first failure load such that, when a load on a backside of the backrest unit exceeds the first failure load, the weakened section fails and the intact section deforms allowing a portion of the backrest unit to tilt forward beyond an upright sitting position to absorb impact energy.