First Ladies Michelle Obama and Laura Bush are to jointly mark the ninth anniversary of the September 11 attacks at the site where the fourth hijacked plane crashed in a Pennsylvania field.
Obama and her predecessor will be the keynote speakers at a ceremony near Shanksville where the heroic acts of the 40 passengers and crew of United Airlines Flight 93 are to be enshrined in a permanent memorial.
"We are deeply honored to welcome First Lady Michelle Obama, Mrs. Laura Bush and all of our guests to this important event," said Neil Mulholland, head of the National Park Foundation, which is behind the memorial.
"Their show of support honors the lives and memories of these 40 heroes and everyone we lost on September 11, and serves as a valuable reminder of how important this memorial is to preserve and share their story."
The 33 passengers and seven crew on Flight 93 wrote themselves into American lore when they mounted an assault against the four Al-Qaeda hijackers that had taken over the plane.
They had learnt of the unfolding strikes via cell phone calls and were caught on a flight recorder trying to break into the cockpit, prompting its suicide pilot to send the Boeing 757 into a fatal dive.
Flight 93 plowed into a field outside Shanksville, killing all on board. The plane came down less than 20 minutes flying time from Washington, its presumed target either the US Capitol or the White House.
At the time, the crash was overshadowed by horrifying scenes at New York's World Trade Center and the Pentagon, turned into infernos by fuel-laden airliners steered on suicide missions by Al-Qaeda hijackers.
The September 11 terror strikes were the most devastating on US soil, costing almost 3,000 lives.
Obama and Bush will be joined at the ceremony at the future site of the Flight 93 National Memorial in Shanksville by Interior Secretary Ken Salazar and Pennsylvania governor Ed Rendell, a statement said.
"Fundraising is currently under way to complete the memorial which is under construction and set for dedication on September 11, 2011," said the statement from the National Park Foundation.
© AFP 2013