DALLAS — Southwest Airlines runs its planes hard. They make many short hops and more trips per day than other U.S. airliners, which adds to wear and tear on parts, including the engines.

As the investigation into last week’s deadly engine failure continues, Southwest CEO Gary Kelly could face questions about whether the company’s low-cost business model — which puts its planes through frequent takeoffs and landings — is putting passengers at risk.

Some aviation safety experts said they see no reason for alarm. And, in fact, Southwest’s safety record is enviable: Until last week, no passenger had died in an accident during its 47-year history.

Still, the Dallas-based airline has paid millions over the past decade to settle safety violations, including fines for flying planes that didn’t have required repairs. Twice in the past nine years, holes have torn open in the roofs of Southwest planes in flight.

In another episode in 2016, an engine on a Southwest jet blew apart over Florida because of metal fatigue, or wear and tear, hurling debris that struck the fuselage and tail. No one was hurt.

Then, last week, one of the engines on Southwest Flight 1380 blew apart at 32,000 feet over Pennsylvania, spraying the Boeing 737 with shrapnel and killing 43-year-old Jennifer Riordan, a mother of two who was blown partway out a broken window. The National Transportation Safety Board said a fan blade that had snapped off the engine was showing signs of metal fatigue.

“They have had a lot” of incidents, said John Goglia, a former NTSB member, “but you have to remember that they have a very large fleet” — more than 700 Boeing 737s, the largest 737 fleet in the world.

Southwest’s short, frequent flights put more stress on the plane and engines, like a car used heavily in stop-and-go city traffic, said Alan Diehl, an aviation-safety consultant and former NTSB and Air Force accident investigator.

Diehl said, however, that Southwest’s crews are accustomed to the quicker pace and that their work is made easier because Southwest flies only Boeing 737s instead of an assortment of planes.

“It’s amazing how safe Southwest has been over the years, considering the operational difficulty of what they do,” said Seth Kaplan of Airline Weekly.