"Southwest expects to cancel approximately 300 flights today to accommodate the inspections," the airline said in a statement, specifying 79 planes were grounded, not the previously announced 81.

"Those aircraft will be inspected over the course of the next several days at five locations." Southwest said the inspections, being conducted with Boeing, are focusing on "aircraft skin fatigue." The National Transportation Safety Board and the Federal Aviation Administration are investigating what caused the fuselage to rip open at 36,000 feet (10,970 meters).

"The safety of our customers and employees is our primary concern, and we are grateful there were no serious injuries," Southwest chief operating Officer Mike Van de Ven said in a statement. A flight attendant and at least one passenger were treated for minor injuries, according to the airline. Passengers told US media they heard a loud bang like a gunshot, and then felt wind rush through the cabin.

"My husband and I looked up, you could see blue sky, you could see the wiring, the cabling," passenger Debbie Downey told CNN.

"We looked at each other and thought, oh my gosh, this is not a good sign." The plane went into a steep nosedive, and oxygen masks were deployed. FAA spokesman Ian Gregor described it as a "rapid, controlled descent" before the plane landed in Yuma. Shawna Redden said her "heart was pounding out of my chest" in the disorienting first minutes of the incident, and she had begun to think that "this is it," but then managed to stay calm and try to help other scared passengers. Redden told Fox News she used her cell phone to text a possible farewell message to her husband, then found herself taking the hand of the stranger next to her "and just praying that we were going to make it down okay."