[dingaling]

Fan and turbine failures are supposed to be contained by the engine casing - it's part of certification. But as we see here, uncontained failures do occur. In general "airplane builders" do the absolute minimum to meet certification so they're not going to add reinforcement to protect against such an event until they're forced Into doing so by the authorities.

Turboprops can't, of course, contain a propellor failure which is why they have a big slab of armour in line with the prop disk. So in that case, yes, safety wins over cost and weight.

[touisteur]

In the case of the Quantas A380 departing from Changi some shrapnel from the engine explosion did go through the aircraft's body, cutting cables, making a mess of the control-command systems. I don't know how one could contain the kind of energy imparted to these metal bits, especially on engines with so much power...

[sam1714]

Fan blade failures are supposed to be contained. Turbine disk failures are not. This leads to several characteristics: disks are life-limited parts where they must be removed after so many cycles, no fuel tanks are within the burst axis of disks, and the flight ceiling of airliners is dictated by the fact that you can get holes and the cabin can (at >1e-9/flight hour) rapidly depressurize.