A pilot error led a Southwest Airlines flight to take off from a closed runway in Portland, Maine, according to an NTSB investigation.

A recent incident involving a Southwest Airlines flight from Portland International Jetport mistakenly took off from a runway closed for construction. The pilots negligence to refer to the airport's safety handbook or make the necessary contact with their dispatcher, according to the National Transportation Safety Board's (NTSB) previous investigations.

The Boeing 737 Max 7 aircraft departed on June 28 for Baltimore without following standard pre-flight procedures to verify the runway's operational status. Despite noticing a vehicle exiting the closed runway, the pilots proceeded with takeoff after not observing any explicit markings or signs indicating closure.

The pilots acknowledged communication attempts regarding their taxi route but missed critical warnings about the runway's closure, according to the NTSB. Favorably, the flight continued without incident, though the incident highlights the importance of rigorous safety protocols in aviation operations.

Southwest Airlines has not yet issued a formal statement regarding the incident. The NTSB's ongoing investigation aims to determine the exact causes and potential safety implications of the oversight.