United Airlines Flight 175

United Airlines Flight 175 was a passenger flight which was hijacked by five al-Qaeda terrorists on September 11, 2001, as part of the September 11 attacks. They deliberately crashed it into the South Tower of the World Trade Center in New York City, killing all 60 people aboard plus the hijackers, and an unconfirmed number in the building's impact zone. The aircraft involved, a Boeing 767–222, was flying United Airlines' daily scheduled morning transcontinental service from Logan International Airport, in Boston, Massachusetts, to Los Angeles International Airport, in Los Angeles, California.

Approximately thirty minutes into the flight, the hijackers forcibly breached the cockpit and overpowered the pilot and first officer, allowing lead hijacker and trained pilot Marwan al-Shehhi to take over the controls. Unlike Flight 11, which turned its transponder off, the aircraft's transponder was visible and the aircraft deviated from the assigned flight path for four minutes before air traffic controllers noticed these changes at 08:51 EDT. They made several unsuccessful attempts to contact the cockpit. Several passengers and crew aboard made phone calls from the plane and provided information about the hijackers and injuries to passengers and crew.

The aircraft crashed into the tower at 09:03. The Flight 175 hijacking was coordinated with that of American Airlines Flight 11, which struck the top of 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 due to the collapse of the tower. 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.