Donald Trump will attend a memorial service in Pennsylvania to honour and remember the victims of hijacked Flight 93 – 17 years on from 9/11.
The president and first lady will participate in a remembrance ceremony in Shanksville, where hijackers crashed a California-bound commercial airliner on 11 September, 2001.
The Pennsylvania field has become a September 11 memorial site.
The 40 passengers and crew members on board attempted to regain control of the jet after speaking to relatives on the phone and learning the hijacking was part of a larger plot targeting the World Trade Centre in Manhattan.
As passengers and crew tried to enter the cockpit to stop the hijackers, the terrorists then made the decision to crash the plane before reaching their final destination – which is believed to have been the Capitol.
A total of 2,966 people died in the worst terror attack on US soil when three other planes were flown into New York’s World Trade Center and the Pentagon in an attack planned by al Qaeda leader Osama bin Laden.
Bin Laden was killed in May 2011 during a US military operation ordered by then-president Barack Obama.
Mr Trump has in the past praised the response of emergency services to the attack.
He was in his Trump Tower penthouse at the time of the attack – four miles from the World Trade Centre.
But the president has also made unsubstantiated claims about what he did on the day of the attacks.
Mr Trump has said, when talking about Muslims, that he watched as “thousands of people were cheering” in Jersey City, New Jersey, situated across the Hudson River from lower Manhattan, as the towers came down.
There is no evidence to support this claim, and there are no news archives that suggest there were any mass celebrations by Muslims.
The president has also previously stated that he lost “hundreds of friends” in the attack on New York.
He has not provided any names but has mentioned knowing a Roman Catholic priest who died while serving as a chaplain to the city fire department.
America’s first couple will visit the newly inaugurated Tower of Voices at the Flight 93 National Memorial – a 93ft monument with 40 wind chimes to represent the 40 passengers and crew killed on the flight.
At 10:03am, the moment when the Boeing jetliner crashed, the names of the victims will be read one by one.
Other memorials taking place to remember the attack include a ceremony at the site where the twin towers once stood.
Hundreds of people, including survivors and families of the victims, will gather and remember the victims by reading the more than 3,000 names of every person who died in the attack and its aftermath.
There will also be moments of silence to mark the times when each plane struck targets in New York, Washington DC and Pennsylvania, and when the two towers fell.
Defence Secretary James Mattis and Vice President Mike Pence will be at a private ceremony at the Pentagon Memorial for the 184 people killed there along with family members.
It comes after Cortlandt Street subway station – the station which served the Twin Towers site which was destroyed in the attack – was finally reopened on Saturday after a $158m reconstruction.
“WTC Cortlandt is more than a new subway station… it is symbolic of New Yorkers’ resolve,” said Joe Lhota, head of the city’s Metropolitan Transportation Authority.