Flight 93 was the fourth plane.
"Today, we also think of the more than 200,000 service members now serving overseas and we think of every citizen who protects our nation at home, including our state, local and federal law enforcement", the president said.
He paid tribute to victims at the new memorial as several services took place around the country to mark 17 years since the terror attacks.
A dedication ceremony for the "Tower of Voices" was held Sunday in Pennsylvania.
The terrorist that day crashed two airliners into the World Trade Center towers in NY and another airliner into the Pentagon. The president, who was accompanied by first lady Melania, called it a "monument to American defiance".
The recent attacks in NY, as well as terror attacks elsewhere, were on Miller's mind on Tuesday (Wednesday NZT) as she arrived.
Thousands of victims' relatives, survivors, rescuers and others are expected at Tuesday's ceremony in Lower Manhattan.
Architect Paul Murdoch said he wanted visitors the crash site to have an emotional reaction when they come to the place where the flight slammed into earth after passengers and crew attacked the terrorists.
Their extended family gathered for the ceremony, including two of Peterás sons - one who's a firefighter and another who's in training.
Thousands of victims' relatives, survivors, rescuers are gathered at the september 11 Memorial in NY.
Footage captured overnight in Johnstown, Pennsylvania, shows US President Donald Trump disembarking Air Force One, striding towards an expectant crowd, and double fist-pumping. A new tower honoring victims was dedicated there Saturday.
During a ceremony at the Pentagon's 9/11 memorial site, where the names of the fallen are etched into a series of benches, Defence Secretary Jim Mattis said those who died did not do so in vain.
In December, a would-be suicide bomber set off a pipe bomb in a subway passageway near Times Square, authorities said.
Copyright 2018 The Associated Press.
One of the hijacked planes on 9/11 - Flight 93 - crashed-landed in a field in that town after passengers bravely fought back against the hijackers and tried to take control back of the aircraft.