Bomb threat clears Boeing campus in Pennsylvania Updated at 12:15 p.m. ET: Authorities are investigating a bomb threat made at a large Boeing plant in Delaware County, Penn. on Tuesday morning. A Boeing spokesperson told NBC News that several hundred employees have evacuated the south campus of the Boeing Plant in Ridley Park, Penn., where the H-47 Chinook helicopter is manufactured. Ridley Park is located southwest of Philadelphia. The evacuations happened between 7:30 and 8:30 a.m. ET, after officials became aware of the threat, The Delaware County Daily Times reported. Bomb-sniffing dogs are going through the facility. According to Ridley Township police, a note was left in a bathroom claiming four explosives were planted inside of one of the hangars, the Daily Times reported. The employees scheduled to work in the affected area of the plant for the current shift have been sent home. Operations are expected to resume at 2:30 p.m. ET, when the next shift begins. Tuesday's threat comes on the same day that marks the 11th anniversary of the 9/11 terrorist attacks. This story is still developing. Please check back for updates. NBCPhiladelphia.com's Kelly Bayliss and Reuters contributed to this story.