A Southwest Airlines Co. 737 Max aircraft being flown to storage after a U.S. grounding order was forced to return to a Florida airport Tuesday because of an engine problem, the carrier said.

The fault on the Boeing Co. jetliner had “absolutely no relation” to the flight-control issue that prompted U.S. regulators to ground all 737 Max aircraft on March 13, said Brandy King, a spokeswoman for Southwest. The engine “performance issue” occurred shortly after the plane left Orlando International Airport at about 2:50 p.m., she said.

The crew of Southwest Flight 8701 declared an emergency shortly after takeoff and landed safely in Orlando, said the Federal Aviation Administration, which is investigating the incident. The Max aircraft was being flown to a storage area in Victorville, California, and only the pilots were on board, Southwest said. The plane was taken to a maintenance hangar after landing.

The FAA grounding allows for airlines to fly 737 Max aircraft that don’t have passengers, and Southwest is gradually shifting its 34 Max jets to Victorville. Boeing and FAA test pilots are also allowed to make flights to demonstrate the software fixes being developed for the planes.

Deadly Crashes

Aviation officials in several countries jumped ahead of the FAA in grounding the Max after an Ethiopian Airlines 737 Max slammed into the ground on March 10. That was less than five months after a Lion Air jet plunged into the Java Sea off the coast of Indonesia on Oct. 29.

The aircraft’s Maneuvering Characteristics Augmentation System, or MCAS, caused the Lion Air jet to dive repeatedly until pilots lost control. The Ethiopian Airlines plane followed a similar flight path. The two crashes killed a combined 346 people.

A U.S. Senate panel is scheduled to hold a hearing Wednesday on the two disasters and federal oversight of air safety.

Boeing fell less than 1 percent to $368.50 after the close of regular trading. The shares dropped as much as 3.1 percent following initial reports of the Southwest plane’s emergency landing, before the carrier identified the cause.