The Federal Aviation Administration says a Southwest Airlines Boeing 737 Max jet made a safe emergency landing Tuesday in Orlando, Florida, after experiencing an apparent engine problem.

The crew declared an emergency after taking off from Orlando International Airport around 2:50 p.m., and landed the plane safely. No passengers were on board. The aircraft was being ferried to Victorville, California, where Southwest is storing the airplanes.

The 737 Max was grounded in the U.S. March 13 after a deadly crash involving a Max on March 10. It was the second fatal crash involving the airplane. U.S. Airlines are allowed to shuttle the planes but cannot carry passengers.

The FAA says it’s investigating but it appears the emergency was not related to anti-stall software suspected in the two fatal crashes.