New York Police Department spokesman Paul Browne said Friday the part includes a clearly visible Boeing identification number. Police haven't said how big the part is.
Browne says the piece of equipment was discovered Wednesday by surveyors inspecting a lower Manhattan building on behalf of the building's owner. He says the inspectors called 911 and police have secured the scene, documenting it with photos.
Police say the medical examiner's office will complete a health and safety evaluation to determine whether to sift the soil around the buildings for possible human remains.
Two hijacked planes slammed into the nearby World Trade Center towers in 2001, killing thousands of people.