The Federal Aviation Administration (FAA) said on Friday it will investigate a Southwest Airlines  flight that departed from a temporarily closed runway in Maine earlier this week.

The FAA said on Tuesday an airport vehicle exited the runway before Southwest Flight 4805, a Boeing 737, began its takeoff roll and departed around 5.45am local time (0945 GMT). Southwest said it is engaged with the National Transportation Safety Board (NTSB) and FAA to understand the circumstances of the departure. After the incident the plane continued safely to Baltimore, Southwest said.

Several other incidents involving Southwest flights in recent months have raised concerns.

Last week, the FAA said it was investigating a Southwest flight that descended to a low altitude of around 500 feet (152.4 m) about nine miles (14.5km) from the Oklahoma City airport.

After the automated Minimum Safe Altitude Warning sounded, an air traffic controller alerted the flight crew of Southwest Airlines Flight 4069, which had departed from Las Vegas.

Earlier this month, the FAA and NTSB said they were investigating a May 25 Southwest flight of a Boeing 737 MAX. The NTSB said the plane experienced a "Dutch roll" at 34,000 feet while en route from Phoenix, to Oakland, California. Such lateral asymmetric movements are named after a Dutch ice-skating technique and can pose serious safety risks.

The FAA said this month it was also investigating a Southwest 737 MAX 8 flight in April that came within about 400 feet of the ocean off the coast of Hawaii after bad weather conditions prompted pilots to bypass a landing attempt at Lihue airport.

During the go-around, the first officer "inadvertently pushed forward on the control column while following thrust lever movement commanded by the autothrottle," according to a June 7 airline memo, and the plane began to descend rapidly, hitting a maximum descent rate of about 4,400 feet per minute.

Southwest said the incident prompted the airline to review data and trends related to its procedures, training, standards, and performance.

  - Reuters