By Daniel Lovering
SHANKSVILLE, PA (Reuters) - Vice President Joe Biden, former President Bill Clinton and former President George W. Bush are among those helping dedicate a memorial on Saturday near Shanksville, Pennsylvania in honor of United Flight 93 that crashed on September 11, 2001.
Forty passengers and crew died on board the aircraft, which fell to the earth during an onboard struggle to thwart hijackers who had seized the plane.
A temporary memorial has stood for a decade at the site in southwestern Pennsylvania, and nearly 1.5 million people have visited.
Saturday's two-hour ceremony, to begin at 12:30 p.m. local time, will include remarks, musical tributes and the laying of wreaths.
Canadian singer-songwriter Sarah McLachlan will perform.
Other dignitaries scheduled to attend include Republican Speaker of the House Rep. John Boehner, Vice President Biden's wife Dr. Jill Biden, former first lady Laura Bush, Secretary of the Interior Ken Salazar, National Park Service Director Jon Jarvis, and Pennsylvania Governor Tom Corbett, organizers said.
President Barack Obama is scheduled to visit the site on Sunday, the 10th anniversary of the attacks.
Flight 93 crashed at 10:03 a.m. on September 11, 2001.
Organizers say $10 million still needs to be raised to complete construction of the Flight 93 National Memorial.
About $52 million has already been raised in public and private funds.
(Editing by Ellen Wulfhorst and Greg McCune)