Question: What was the destination of the United Airlines flight hijacked by Ahmed al-Haznawi and three others on September 11?

Context paragraphs:
LeRoy Homer Jr.: LeRoy Wilton Homer Jr. (August 27, 1965September 11, 2001) was the First Officer of United Airlines Flight 93, which was hijacked as part of the September 11 attacks in 2001, and crashed into a field near Shanksville, Pennsylvania, killing all 37 passengers and seven crew members.

Khalid Abdalla: Khalid Abdalla (Arabic: خالد عبد الله‎ ‎ , "Khālid ‘Abd Allāh"; born 26 October 1980) is a British Egyptian actor and activist.  He came to international prominence after starring in the 2006 Academy Award-nominated and BAFTA-winning film, "United 93".  Written and directed by Paul Greengrass, it chronicles events aboard United Airlines Flight 93, which was hijacked as part of the September 11 attacks.  Abdalla played Ziad Jarrah, the pilot and leader of the four hijackers on board the flight.  He starred as Amir in "The Kite Runner" and acted with Matt Damon in "Green Zone", his second film with director Paul Greengrass.  Abdalla appears as himself in Jehane Noujaim's documentary on the ongoing Egyptian revolution, "The Square", which won the Audience Award at Sundance Festival in 2013.

Hamburg cell: The Hamburg cell (German: "Hamburger Zelle" ) or Hamburg terror cell (German: "Hamburger Terrorzelle" ) was, according to U.S. and German intelligence agencies, a group of radical Islamists based in Hamburg, Germany that included students who eventually came to be key operatives in the 9/11 attacks.  Important members included Mohamed Atta, who led the four hijacking teams in 2001 and piloted American Airlines Flight 11; Ramzi bin al-Shibh, who conspired with the other three members but was unable to enter the United States; and Marwan al-Shehhi, who piloted United Airlines Flight 175, Ziad Jarrah, who piloted United Airlines Flight 93 and failed to hit a target in Washington D.C., claimed by Khalid Sheikh Mohammed to have been the Capitol.  Less important members included Said Bahaji, Zakariya Essabar, Mounir el-Motassadeq, and Abdelghani Mzoudi.

United 93 (film): United 93 is a 2006 biographical drama-thriller film written, co-produced and directed by Paul Greengrass, that chronicles events aboard United Airlines Flight 93, which was hijacked during the September 11 attacks of 2001.  The film attempts to recount with as much veracity as possible (there is a disclaimer that some imagination had to be used) and in real time (from the flight's takeoff) what has come to be known in the United States as a critical moment.  According to the filmmakers, the film was made with the cooperation of all of the passengers' families.  The majority of the film is presented in real time.

Flight 93 National Memorial: The Flight 93 National Memorial is located at the site of the crash of United Airlines Flight 93, which was hijacked in the September 11 attacks, in Stonycreek Township, Somerset County, Pennsylvania, about 2 mi north of Shanksville, and 60 mi southeast of Pittsburgh.  The memorial was made to honor the passengers and crew of Flight 93, who stopped the terrorists from reaching their target by fighting the hijackers.  A temporary memorial to the 40 victims was established soon after the crash, and the first phase of the permanent memorial was completed, opened, and dedicated on September 10, 2011.  The design for the memorial is a modified version of the entry "Crescent of Embrace" by Paul and Milena Murdoch.

1990 Guangzhou Baiyun airport collisions: On 2 October 1990, a hijacked Boeing 737, operating Xiamen Airlines Flight 8301, collided with two other aircraft on the runways of the old Guangzhou Baiyun International Airport, while attempting to land.  The hijacked aircraft struck a parked China Southwest Airlines Boeing 707 first, inflicting only minor damage, but then collided with China Southern Airlines Flight 2812, a Boeing 757 waiting to take off, flipping onto its back.  A total of 128 people were killed, including seven of nine crew members and 75 of 93 passengers on Flight 8301 and 46 of 110 passengers on Flight 2812.

Ahmed al-Haznawi: Ahmed Ibrahim al-Haznawi (Arabic: احمد ابراهيم الحزناوي الغامدي‎ ‎ , "Aḥmad Ibrāhīm al-Ḥaznāwī" ) (October 11, 1980 – September 11, 2001) was one of four hijackers of United Airlines Flight 93 as part of the September 11 attacks.

United Airlines Flight 93: United Airlines Flight 93 was a domestic scheduled passenger flight that was hijacked by four Al-Qaeda terrorists on board, as part of the September 11 attacks.  It crashed into a field in Somerset County, Pennsylvania, during an attempt by the passengers and crew to regain control.  All 44 people aboard were killed, including the four hijackers, but no one on the ground was injured.  The aircraft involved, a Boeing 757–222, was flying United Airlines' daily scheduled morning flight from Newark International Airport in New Jersey to San Francisco International Airport in California.

Jeremy Glick: Jeremy Logan Glick (September 3, 1970 – September 11, 2001) was a passenger on board United Airlines Flight 93, which was hijacked and crashed as part of the September 11 attacks.  Aware of the earlier attacks at the World Trade Center, Glick and some of his fellow passengers attempted to foil the hijacking.  During a struggle to reclaim the aircraft, it crashed into a field in Stonycreek Township near Shanksville, Pennsylvania, killing all 33 passengers and seven crew members on board.

Todd Beamer: Todd Morgan Beamer (November 24, 1968 – September 11, 2001) was an American passenger aboard United Airlines Flight 93, which was hijacked as part of the September 11 attacks in 2001.  He was one of the passengers who tried to reclaim the aircraft from the hijackers, leading them to crash it into a field in Stonycreek Township near Shanksville, Pennsylvania.

Supporting paragraphs: Ahmed al-Haznawi United Airlines Flight 93
Answer: San Francisco