A Southwest Airlines Co Boeing 737 MAX 8 aircraft without passengers and the type that was grounded two weeks ago, landed safely on Tuesday afternoon in Orlando, Florida, after declaring an emergency over an engine-related problem, the US Federal Aviation Administration said.

Southwest Flight 8701 was headed from Orlando International Airport to Southern California Logistics Airport, an aircraft storage facility in Victorville, following the FAA's grounding of the plane after two fatal crashes in less than five months.

The jet took off at 2:47 pm ET and landed back at the airport at 2:58 pm, according to flight tracker FlightAware.

The FAA said it is investigating the incident. Southwest had no immediate comment.

The FAA grounded the Boeing 737 MAX following two fatal crashes since October but has allowed airlines to conduct flights without passengers to move planes to other airports. A Boeing spokesman said the company was "aware of the incident and supporting our customer."

Southwest has 34 MAX 8s in its fleet, the most of any US carrier. American is next at 24. United Airlines has 14.

Southwest said on March 23 it was starting to move its entire MAX fleet to a facility in Victorville, at the southwestern edge of the Mojave Desert, while the global grounding remains in effect.

"The planes being in one place will be more efficient for performing the repetitive maintenance necessary for stationary aircraft, as well as any future software enhancements that need to take place," spokeswoman Brandy King said.

An Ethiopian official said on Tuesday that a preliminary report on the crash of the Boeing 737 MAX aircraft that killed 157 on March 10 will be made public later this week.

The final report may take months to complete, but a preliminary report may be released "anytime soon," said the spokesman for Ethiopia's transport ministry.

There is speculation that software could have contributed to the crash as well as to the crash of another Boeing 737 MAX, a Lion Air flight in Indonesia in October. Boeing is updating the plane's anti-stall software and has invited more than 200 pilots, technical experts and regulators to its factory in Renton, Washington, on Wednesday for a briefing.

On Wednesday the Senate will hold a hearing about the 737 MAX aircraft.

The Associated Press contributed to this story.