Marwan al-Shehhi

Marwan Al-Shehhi was one of the 19 9/11 hijackers, and is believed to be the one who flew United 175 into the South Tower of the World Trade Center.

Attacks
According to the 9/11 Commission Report, Shehhi made a 3-minute call to Mohamed Atta (6:52-6:55 a.m.) on September 11, 2001, from within Logan International Airport as both American 11 and United 175 were to fly from Boston Logan to LAX. This is thought to have been a final confirmation that both teams were ready and waiting to depart for their scheduled flights, and they decided which building they had to hit (the building with antenna i.e. north tower) was confirmed by atta during that conversation according to FAA.

Shehhi boarded United 175 at 7:27 a.m. Around 30 minutes into the flight, between 8:42 and 8:46 a.m., the plane was hijacked. During the flight, the plane narrowly avoided a mid-air collision with another aircraft, Delta Airlines Flight 2315. Several calls were made from the plane to relatives, the passengers learning of the fate of American 11.

The plane was flown into the South Tower of the World Trade Center at 9:03:02 a.m. The plane crashed with a speed of approximately 590 mph (950 km/h). The plane was carrying about 10,000 gallons (37,850 litres) of jet fuel. It was seen live on television around the world as it crashed into the South Tower, being filmed from multiple vantage points.

Shehhi flew the plane faster and lower into the tower than Atta did, into the eastern half of the South Tower's southern facade close to the southeast corner, leading to the South Tower collapsing before the North Tower; which was the first to be hit.