On our 20 year old 5th wheel one of the leaf springs snapped just as we turned onto our street. Luckily it didn't happen while on the highway.
I'm guessing what may have happened was we hit a bad bump on the freeway. It was so bad my wife who was following in her car said all of the wheels of the 5th wheel came off the ground. Then the turn onto our street is very off camber and a big dip which puts all the stress on the side where the leaf broke. The bump weakened it and the turn snapped it.
I replaced all 4 springs so we should be good for another 20 years.