The airline has not canceled any flights today, and the majority of the planes removed from service have been returned, spokeswoman Christi Day said.
Removing the aircraft from service caused flight delays and cancellations throughout Southwest's service area Wednesday.
"It was minimal, approximately 4 percent of our flights," according to Southwest spokeswoman Brandy King.
Flights are running on schedule at Oakland International Airport, the airport duty supervisor said this morning.
San Francisco International Airport's duty manager was unable to provide specifics regarding flight cancellations.
Norman Y. Mineta San Jose International Airport officials could not be reached for comment.
