At least four of the seven flight attendants who will be on United Airlines Flight 175—the second plane to hit the World Trade Center—on 9/11 are not originally supposed to take this flight, and are only assigned to be on it shortly before September 11: 
Amy Jarret will be on Flight 175 because she switches shifts with one of the original attendants, Elaine Lawrence. [San Francisco Chronicle, 10/23/2001] Robert Fangman takes the place of attendant Elise O’Kane, who accidentally enters an incorrect code into the computer when signing up for flights, and is instead scheduled for flights to Denver during September 2001. [Boston Globe, 5/22/2005; CNN, 10/8/2005] Lauren Gurskis reschedules herself to a September 12 flight so she can drive her son to his first day of kindergarten. Kathryn Laborie is most likely the attendant who takes her place. [Boston Globe, 9/8/2002] Barbara McFarland swaps shifts with another attendant so she can spend an extra day with her son. The attendant that replaces her is unstated. [Cape Cod Times, 9/14/2001; Cape Cod Times, 3/10/2002]
Many of the flight attendants who will be on the other three hijacked planes are also only assigned to those flights shortly before 9/11 (see Shortly Before September 11, 2001-Early Morning September 11, 2001, Shortly Before September 11, 2001-Early Morning September 11, 2001, and Shortly Before September 11, 2001).
September 10, 2001: Suspicious Passengers on Flight to Boston Ask about WTC
The night before 9/11, two men are observed behaving suspiciously on a United Airlines flight from San Diego to Boston. This is according Elaine Lawrence, who is one of the plane’s flight attendants. She later recalls that the men—one who appears Middle Eastern, the other Caucasian—upgrade from coach to first class, and then sit “on the left side of the plane, seats 3A and 3B,” near the cockpit door. She will comment: “It was really weird. They didn’t eat, they didn’t sleep, they didn’t watch the movie. Why upgrade?” Furthermore, she recalls: “[W]hen we were getting close to Boston they asked if we could see the World Trade Center towers. ‘Do we see the towers?’ the guy kept asking. I told him we wouldn’t be going by New York.” After the attacks the following day, she will call the FBI and inform them of this incident. Lawrence was in fact originally scheduled to be an attendant on Flight 175—the second plane to hit the WTC—on 9/11. However, as she is planning to go on vacation, she has traded shifts with another flight attendant, Amy Jarret (see Shortly Before September 11, 2001). [San Francisco Chronicle, 10/23/2001]
