It is thought the terrorists who hijacked Flight 93 were planning to crash the plane into the White House but crashed en route.
The 9/11 plane strikes, which destroyed the Twin Towers and left a gaping hole in the Pentagon, killed almost 3,000 people, a lot of them in Manhattan.
How hard is it to write a thoughtful message to the families of those lost in the attack, thank the first responders, encourage America, or at the very very least, not pump your fists?
Commemorations also took place in NY and Washington to mark the anniversary of the 9/11 attacks by al Qaeda, in which almost 3,000 people were killed.
President Donald Trump on Tuesday lauded the men and women of United Flight 93 for saving countless lives when they struggled with hijackers on September 11, 2001 and called the field where the plane went down a monument to "American defiance".
The passengers who died in Shanksville have been hailed as heroes ever since.
White House Press Secretary Sarah Huckabee Sanders said the president's focus for the day was "remembering the lives that were lost, and certainly honouring the individuals who were not only lost that day, but also put their lives on the line to help in that process".
A stark reminder came not long after last year's anniversary: A truck mowed down people, killing eight, on a bike path within a few blocks of the World Trade Center on Halloween.
Delivering his speech at the newly inaugurated Tower of Voices memorial, Trump told the families of the victims of Flight 93 that their loved ones "stopped the forces of terror".
The sound the chimes make will change depending on the strength and direction of the wind.
The site is where hijackers crashed a commercial airliner on September 11, 2001, after the 40 passengers and crew members realized what was happening and tried to storm the cockpit.
Seventeen years after losing her husband, Margie Miller went to the New York City ceremony from her home in suburban Baldwin. Vice President Mike Pence represented the administration there on Tuesday. The annual 9/11 commemorations are by now familiar rituals, centered on reading the names of the dead.