Klokken 9:37 styrede en anden gruppe af flykaprere [[American Airlines' flynummer 77]] ind i Pentagon.<ref>{{cite web |url=http://www.ntsb.gov/info/Flight_%20Path_%20Study_AA77.pdf |title=Flight Path Study – American Airlines Flight 77 |publisher=National Transportation Safety Board |date=19. februar 2002 |format=PDF}}</ref> Det fjerde fly, United Airlines' flynummer 93, styrtede ned nær Shanksville i Pennsylvania, efter at der opstod en kamp mellem de ombordværende passagerer og flykaprerne. Flyets endelige mål antages at have været enten United States Capitol (mødestedet for den amerikanske kongres) eller [[Det Hvide Hus]].<ref name="Chap7">{{cite book |chapter=The Attack Looms |url=http://govinfo.library.unt.edu/911/report/911Report_Ch7.htm |year=2004 |title=9/11 Commission Report |publisher=National Commission on Terrorist Attacks Upon the United States |access-date=2. juli 2008}}</ref><ref>{{cite web |url=http://www.ntsb.gov/info/Flight%20_Path_%20Study_UA93.pdf |title=Flight Path Study – United Airlines Flight 93 |publisher=National Transportation Safety Board |date=19. februar 2002 |format=PDF}}</ref>
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