I recall that when Sully Sullenberger landed US Air flight 1549 in the Hudson River, someone (here I think) said that under-wing engines were designed to detach to prevent the wings from breaking off in the event of water landing.
That may have been idle speculation, I can't remember. Something about shear pins.
Quickly perusing aviation transport forums I see that at least some jet turbine engine mounting systems have bolts that are designed to shear given a high enough lateral load. There are generally only 3 or 4 bolts, with each mount specialized to accommodate a normal load in a specific plane but all designed to breakaway if necessary.
I had dinner with Sully. He is a heck of a nice guy. Yeah, I know, name-dropping. ;-)
We discussed the sequence of events. Never heard him say that. Now, he did say he kept the nose up as high as he could in an effort to reduce speed so when the engines did hit the water, chances were reduced that the engines digging in would cause the jet to tumble and break apart.