BOSTON – A US Airways Express plane that took off from Knox County Airport in Owls Head on Tuesday afternoon was discovered to be carrying a cutting object found when the plane landed at Boston’s Logan Airport.

“Our flight crew found a box cutter on the airplane, and then that was turned over to the authorities, and then the passengers boarded and the flight continued on to Syracuse, [N.Y.],” said Deborah Thompson, spokeswoman for US Airways.

The crew discovered the object during a routine inspection of the plane, said Ann Davis, spokeswoman for the Transportation Security Administration.

“It was an inbound flight. There was no penetration through our security,” Massachusetts Port Authority spokesman Phil Orlandella said.

The TSA and the FBI are investigating the incident, Davis said.

The plane, US Airways Express Flight 4971, had arrived from Knox County Airport and had no passengers aboard when the blade was found, Davis said.

Greg Grotton, Knox County Airport manager, confirmed Tuesday night that he had been contacted by an official who told him “they found something on the aircraft” in Boston. Grotton said he was not told what was found, only that the plane’s last stop before landing at Logan was at Knox County Airport.

Grotton said a key question that needs to be answered is how long the box cutter had been on the plane. According to the US Airways Web site, the flight originated in Boston on Tuesday, leaving Logan at 12:15 p.m. and landing at Knox County at 1:03 p.m. It was scheduled to leave Knox County at 1:25 p.m. for the return flight to Boston.

Grotton said the flight often stops either at Bar Harbor or Augusta before landing at Knox County then continuing on to Boston. There is no record it did so Tuesday.

“I don’t think they know if whatever it was was already on the plane when it landed here,” Grotton said.

Grotton said he planned to meet with investigators early today.

It was the second US Airways plane on which a cutting tool was found Tuesday.

Passengers were evacuated from a plane at Philadelphia International Airport on Tuesday after a box cutter was discovered aboard the flight, officials said.

The razor-blade tool was found at about 3:35 p.m. on a US Airways jet that had arrived from Houston and was about 20 minutes away from a scheduled departure for Phoenix, according to airport spokesman Mark Pesce.