For the second time this week, a Southwest Airlines plane has aborted a takeoff at Chicago's Midway International Airport.

Federal Aviation Administration spokeswoman Elizabeth Isham Cory says the crew reported problems with one if its engines as the plane moved down the runway to begin its takeoff Friday morning. The FAA will investigate.

Southwest said the Philadelphia-bound plane with 136 passengers returned to the gate after the pilot of another Southwest aircraft reported seeing "potential signs of a mechanical issue." Spokeswoman Emily Samuels says an initial review found nothing wrong but the aircraft remains in maintenance.

On Wednesday night, a Southwest plane headed to Boston from Midway cut short its takeoff because of a mechanical issue. The Chicago Fire Department said one of that plane's engines caught fire.