175 hijacking was coordinated with that of American Airlines Flight 11, which struck the top of Tower One (the North Tower) 17 minutes earlier. The crash of Flight 175 into the South Tower was the only impact seen live on television around the world as it happened. The impact and subsequent fire caused the South Tower to collapse 56 minutes after the crash, resulting in hundreds of additional casualties. During the recovery effort at the World Trade Center site, workers recovered and identified remains from Flight 175 victims (see the Aftermath section below), but many other body fragments could not be identified.

In early September 2001, the Flight 175 group of hijackers arrived in Boston from Florida. Hamza al-Ghamdi and Ahmed al-Ghamdi arrived together on September 7 and checkedinto the Charles Hotel in Cambridge, Massachusetts. The next day, they relocated to the Days Inn in Boston. Fayez Banihammad flew from Florida to Boston, along with Mohand al-Shehri, on September 8, and they checked into the Milner Hotel in Boston. Marwan al-Shehhi arrived in Boston on September 9 and stayed at the Milner Hotel, where he shared a room with Flight 11 hijacker Mohamed Atta.[3]

The flight was operated with a Boeing 767-200, registration number N612UA, built and delivered in 1983,[4] with capacity of 168 passengers. It had 168 seats (10 in first class, 32 in business class, and 126 in economy class). On the day of the attacks, the flight carried only 56 passengers and 9 crew members, which represented a 33 percent load factor — well