Scores of Southwest Airlines travelers are facing delays or cancellations Sunday due to emergency inspections following the midair explosion of an engine on one of the airline's Boeing 737s last week.

Southwest said about 40 of its 4,000 scheduled flights were canceled because of the emergency fan blade inspections. Meanwhile, the flight-tracking website FlightAware showed that more than 500 Southwest flights, or about 13 percent, had been delayed Sunday.

Southwest did not immediately say what proportion of the delays was tied to the engine inspections or whether another problem was contributing to the widespread disruptions. In a statement, it only acknowledged the cancellations.

"When we announced the accelerated engine fan blade inspection program on Tuesday night, we said there would be some impact to the operation," Southwest's communications team said in a statement. "We have minimized flight disruptions this past week through actions such as proactive aircraft routings to cover open trips and utilizing spare aircraft, when available."

Following the Tuesday incident, which resulted in the death of 43-year-old passenger Jennifer Riordan after she was partially sucked out of a blown-out window, Southwest announced accelerated ultrasonic checks of fan blades on the CFM56 engines, which power the 737s that make up the entirety of Southwest's fleet.

"The accelerated inspections are being performed out of an abundance of caution and are expected to be completed over the next 30 days," Southwest said in a statement last Wednesday.

The Federal Aviation Administration later ordered inspections on the type of engine that exploded.

Southwest said, however, the cancellations stemmed from its voluntary inspections -- not the FAA directive issued Friday. The airline said some of the delays Sunday were caused by strong thunderstorms in the Southeast.