Former Homeland Security Secretary Tom Ridge will be one of the featured guests next Sunday to mark the fourth anniversary of the crash of United Airlines Flight 93 in Somerset County.

Ridge, along with U.S. Sen. Rick Santorum, R-Pa., is scheduled to speak at the anniversary ceremony, which begins at 9:30 a.m. at the temporary memorial site on Skyline Road in Stonycreek Township.

Several family members of the victims are also expected to attend. Gov. Ed Rendell and current Homeland Security Secretary Michael Chertoff have been invited but have not yet confirmed they will attend.

The plane, carrying 40 passengers and crew members, left Newark, N.J. the morning of Sept. 11, 2001, and was headed for San Francisco when it was hijacked by terrorists. Investigators believe the attackers planned to fly the plane into Washington, D.C., and possibly crash it into the U.S. Capitol or White House.

The plane crashed in an empty field near Shanksville.

Following the ceremony at the crash site Sunday, the victims and their families will be honored at half-time of the Steelers season opener at Heinz Field in Pittsburgh.

Though the ceremony will be short, it is expected to include a video presentation and a call for donations for the construction of the permanent memorial.

The winning design for the memorial is scheduled to be announced Wednesday in Washington, D.C. More than 1,000 designs were submitted from around the world. Those entries were narrowed down to five finalists, and a jury of professionals, laypeople and victims' relatives chose the winner in August.

In preparation for the anniversary events at the crash site, the temporary memorial will close at 6 p.m., next Saturday and reopen for the ceremony at dawn next Sunday.

A shuttle will be provided to take visitors from the parking lot to the ceremony. Those attending are asked to arrive by 9:15.