An American Airlines flight destined for Boston was delayed after a security breach that left a door unlocked as the plane sat on the tarmac overnight.The lapse was discovered when two passengers walked onto the plane and took seats several hours ahead of the scheduled boarding time without showing a boarding pass to airline personnel.Francesco Dedos and his 21-year-old daughter flew from Philadelphia to Boston after they boarded the plane around 6 a.m. and put their luggage on the plane without showing a boarding pass to airline personnel. "Someone went through the door first," Dedos said, through a translator. "We followed him."A passenger on the plane told NewsCenter 5 the captain of American Airlines Flight 1655 said the jetway door was not locked overnight. "The pilot said the jetway door was open overnight," Neil Ungerleider, a passenger on the plane said. "The plane was not secure overnight," the pilot added. The captain originally said the passengers were on the wrong flight, but American Airlines said they determined the couple was on the correct flight to Boston. A spokesperson for American Airlines said the two passengers went back out to the gate area to wait after putting their luggage in the aircraft. All passengers were told to get off the plane and the plane was swapped out of an abundance of caution. "This has certainly been an interesting morning," the flight's captain said. "It was a difficult decision to make, but I am sure you agree a necessary one."   The plane's departure to Boston was scheduled for 8 a.m. American Airlines said the airport is responsible for making sure that the jetway is locked. Philadelphia International Airport said they are looking into the incident. Statement from American Airlines"Two passengers gained unauthorized access to one of our aircraft earlier this morning. Out of an abundance of caution, we are utilizing a different aircraft for the flight to Boston. We apologize to our customers for the inconvenience."Get the WCVB News App