It's happened before where the protective cover didnt do its job and a part of an engine hit the plane as it came apart.
The engine failure was reminiscent of a similar event on a Southwest Boeing 737-700 jet in August 2016 as it flew from New Orleans to Orlando, Florida. Shrapnel from the engine left a 5-by-16-inch hole just above the wing. Passenger oxygen masks dropped from the ceiling. Pilots landed the plane safely in Pensacola, Florida.
NTSB investigators said one of the engine's fan blades broke off from the hub during the flight. The broken edge of the blade showed crack lines consistent with metal fatigue.
http:// www.chicagotribune.com/news/nationworld/ct-southwest-airlines-emergency-landing-20180417-story.html