Safety fears surrounding the Boeing 737 Max 8 show no signs of easing. A Southwest Airlines-owned model of the grounded jet—that was on its way to storage—was forced to make an emergency landing shortly after departing Orlando on Tuesday afternoon. It took off from Orlando International Airport at 2:50 p.m. and returned to the airport just before 3 p.m. after pilots reported some kind of engine problem. There were no passengers on board—at the moment, the planes are only allowed to fly in special circumstances, such as when being transferred to storage. The jet is one of hundreds grounded around the world while investigators work out what caused the Ethiopian Airlines crash that killed 157 people this month. That crash came after a Lion Air accident in October that killed all 189 people aboard when it plunged into the Java Sea in Indonesia.