Several dozen people were killed in Shanksville, Pennsylvania when United Flight 93 crashed into a field. Casualties could have been much higher if the passengers hadn't confronted the hijackers. Susan Jhun has more on how the heroism of those men and women is being remembered.

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PENNSYLVANIA -- Reflection and remembrance of the 40 passengers and crew members of Flight 93.

Sunday, those on Flight 93 were honored by friends and families at the new Flight 93 National Memorial at a National Park near Shanksville.

"We gather here to remember ordinary men and women who did an extraordinary act of courage."

The names of those known as the heroes of Flight 93 were read aloud with nearly 5,000 gathered in attendance. Theirs was the fourth aircraft hijacked by terrorists on 9/11. The plane was headed to Washington when passengers and crew using air phones learned of the other hijacked planes and realized the fate of their flight. They stormed the cockpit, thwarting an attack on the U.S. Capitol.

"They preferred to shorten the final minutes of their own lives to defend their nation," said Pennsylvania Governor Tom Corbett.

"They stood up. Ordinary civilians. Citizens just like us and they took action," said Congressman Mark Critz.

"We wondered, would we? Could we? Had we been in your place, shown the same resolve. The same selflessness. The same astonishing valor," said Tom Ridge, former U.S. Secretary of Homeland Security.

Those in attendance at the service stood at the Wall of Names of the victims of Flight 93 remembering the bad and the good.

"Although the darkest side of humanity was certainly aboard Flight 93 that day, the very best of our humanity was on board as well," said John Hendricks, Founder of Discovery Communications.

After the ceremony ended, President Obama paid a visit to the memorial, laying a wreath to remember those who sacrificed so much.