If I, as an engineer, sign of on changing the screws on the flaps for cheaper ones and the plane crashes because the flaps go loose due to the screws being unab

If I, as an engineer, sign of on changing the screws on the flaps for cheaper ones and the plane crashes because the flaps go loose due to the screws being unable to handle the stress, my career can be assumed over if I have no good explanation. If an engineer signs off a change they sign that they have validated all the constraints and that for all they know the machine will work within the specs with no faults. If a software engineer commits code we may run some tests over it, look a bit over it. That's fine. But if the software ends up killing anyone, the software engineer is not responsible. And yes, to my knowledge, every change to an aircraft is tested before flight or atleast validated by an engineer that understands what was just changed.