The Federal Aviation Administration (FAA) has opened an investigation after two United Airlines passengers were injured last week as pilots responded to an onboard alert. United Airlines Flight 2428 from New Jersey was descending into San Francisco International Airport on Thursday when pilots were notified "that another aircraft was in the vicinity," the FAA said. The aircraft "slowed its descent to account for another aircraft at a lower altitude" while the seatbelt sign was on, a United Airlines spokesperson told The Hill. "Two customers, including one who was out of their seat at the time, reported possible injuries and were transported to a hospital," United said. The aircraft landed safely in San Francisco, the FAA reported. "We're grateful to our crew for their efforts to ensure the safety of our employees and customers," United said. There was no additional information about the condition of the passengers.