(CNN) -- Federal officials are investigating how firecrackers got into a Southwest Airlines plane scheduled to leave Las Vegas on Tuesday. Southwest Airlines Flight 2408 was leaving Las Vegas McCarran International Airport and was headed to Kansas City, Missouri. The flight was delayed for an hour when a flight attendant found a plastic bag with firecrackers underneath a seat, said Ashley Dillon, an airline spokeswoman. Passengers deplaned. After an inspection that included re-screening luggage, the Transportation Security Administration declared the plane safe and allowed passengers to re-board. It landed safely in Kansas City an hour behind schedule, the spokeswoman said. None of the passengers claimed the plastic bag, but the TSA said it is investigating how the prohibited items got onto the aircraft.
The Southwest Airlines flight was leaving Las Vegas for Kansas City, Missouri . After an inspection that included re-screening luggage, it was declared safe .