Lomapaseo is right, there is no FAA regulation how to build an airplane. Boeing adopts the design philosophy that the engine should shear off in case of impact on water or ground. Hence the engines are attched with shear pins on the Fat Bobby.
Airbus on the other hand adopts the design philosophy that the engine should stay on the wind in all cases and uses a redundant sleeve/bolt design.
There is no right or wrong here!
Me thinks that the Airbus philosophy helped ditching US Air succesfully into the Hudson and the Boeing design route certainly minimised casualties in the case we are discussing here.