FILE- This Monday, May 2, 2011 file photo shows visitors to the temporary memorial to United Flight 93 as they overlook the crash site in Shanksville, Pa. In one sense, Shanksville is a tiny village far from major cities and cultural attractions. But the crash of Flight 93 in a field there on Sept. 11, 2001 has brought visitors from around the world to the national park site that now marks the spot where the hijacked plane came down. (AP Photo/Gene J. Puskar, FILE)

FILE- This Thursday, June 16, 2011 file photo shows a sign describing the plan for the entire Flight 93 memorial on the fence at the temporary memorial as construction continues at the Flight 93 Memorial in Shanksville, Pa. The first phase of the construction is set to be completed and dedicated on Sept. 10, 2011, one day before the tenth anniversary of the crash of United Flight 93 into a field during the attacks of Sept. 11, 2001. In one sense, Shanksville is a tiny village far from major cities and cultural attractions. But the crash of Flight 93 in a field there on Sept. 11, 2001 has brought visitors from around the world to the national park site that now marks the spot where the hijacked plane came down. (AP Photo/Keith Srakocic, FILE)

One of the many memorials at the temporary memorial at the crash site of United Flight 93 in Shanksville, Pa. is seen pointing toward the impact area Friday, April 28, 2006. The film "United 93" opens Friday, depicting the way the passengers and crew confronted hijackers on that flight on Sept. 11, 2001, (AP Photo/Keith Srakocic)

FILE- This Friday, July 22, 2011 file photo shows construction as it continues in the plaza area of the permanent Flight 93 Memorial site in Shanksville, Pa. The work and preparation continue for the dedication and opening of the first phase of the memorial in honor of those who perished in the crash of United Flight 93 in the attacks of September 11, 2001. In one sense, Shanksville is a tiny village far from major cities and cultural attractions. But the crash of Flight 93 in a field there on Sept. 11, 2001 has brought visitors from around the world to the national park site that now marks the spot where the hijacked plane came down. (AP Photo/Keith Srakocic, FILE)

FILE- This Thursday, June 16, 2011 photo shows construction as it continues at the site of the visitors center at the Flight 93 Memorial in Shanksville, Pa. The first phase of the construction is set to be completed and dedicated on Sept. 10, 2011, one day before the tenth anniversary of the crash of United Flight 93 into a field during the attacks of Sept. 11, 2001. In one sense, Shanksville is a tiny village far from major cities and cultural attractions. But the crash of Flight 93 in a field there on Sept. 11, 2001 has brought visitors from around the world to the national park site that now marks the spot where the hijacked plane came down. (AP Photo/Keith Srakocic, FILE)

FILE- This Monday, Aug. 1, 2011 file photo shows visitors to the temporary Flight 93 memorial in Shanksville, Pa., as they look out over a grove of sweet gum trees that were donated to the Flight 93 National Memorial by the organizers of the Sept. 11 Memorial in New York. In one sense, Shanksville is a tiny village far from major cities and cultural attractions. But the crash of Flight 93 in a field there on Sept. 11, 2001 has brought visitors from around the world to the national park site that now marks the spot where the hijacked plane came down. (AP Photo/Gene J. Puskar, FILE)

FILE - In this Tuesday, Sept. 11, 2001 file photo, emergency workers look at the crater created when United Airlines Flight 93 crashed near Shanksville, Pa. (AP Photo/Keith Srakocic)

FILE- This Monday, Aug. 1, 2011 file photo shows the 17-ton boulder, left, that was placed to mark the site of the crash of Flight 93 at the Flight 93 Memorial in Shanksville, Pa. In one sense, Shanksville is a tiny village far from major cities and cultural attractions. But the crash of Flight 93 in a field there on Sept. 11, 2001 has brought visitors from around the world to the national park site that now marks the spot where the hijacked plane came down. (AP Photo/Gene J. Puskar, FILE)

FILE - In this Aug, 1, 2011 file photo, flags hang on a fence overlooking the crash site of Flight 93 in Shanksville, Pa. In one sense, Shanksville is a tiny village far from major cities and cultural attractions. But the crash of Flight 93 in a field there on Sept. 11, 2001 has brought visitors from around the world to the national park site that now marks the spot where the hijacked plane came down. (AP Photo/Gene J. Puskar, File)