ORLANDO, Fla. (AP) — A Southwest Airlines Boeing 737 Max made a safe emergency landing Tuesday in Orlando, after experiencing an engine problem.

The FAA said the crew declared an emergency after taking off from Orlando International Airport around 2:50 p.m., and returned to the airport safely. No passengers were on board, and 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 in Ethiopia on March 10. It was the second fatal crash involving the airplane. Airline companies are allowed to shuttle the planes but can’t carry passengers.

The FAA says it’s investigating but the emergency was not related to anti-stall software that is suspected as a cause of the two fatal crashes.