Everything was going smoothly until Southwest Airlines Flight 1380 reached about 32,000 feet. Then there was chaos.

A deafening bang. A puff of gray smoke. Oxygen masks dropped. At first, the plane vibrated violently side to side. Then it lunged to the left. In the cockpit, alarms and warnings rang out — so loud that the pilots had to scream to talk to each other.

“And that all kind of happened all at once,” Darren Ellisor, the flight’s first officer, told ABC News’s “20/20” in an interview that will be broadcast Friday night.

Captain Tammie Jo Shults, who was next to him in the cockpit during the April 17 flight, was not initially supposed to be in that seat. Her husband, Dean Shults, a fellow Southwest pilot, had agreed to swap flights so she could attend their son’s track meet.