Sandy Dahl: 9/11 pilot widow dies (VIDEO)

Sandy Dahl, the widow of the man who flew United Flight 93 that crashed into a Pennsylvania field after being taken over by terrorists on 9/11, has died of natural causes.

According to the Denver Post, Dahl, 52, passed away in her sleep near Denver, said family friend David Dosch.

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Dahl had worked tirelessly to run the Captain Jason M. Dahl Scholarship Fund, and her death came as a surprise, reported CNN. The charity, which she started in her husband's name, allows aspiring pilots to attend commercial flight training schools with monetary scholarships.

Captain Dahl became a hero when he and his passengers on United Flight 93 fought back against hijackers who seized the plane on 9/11, according to The Telegraph. The flight came down in a field in rural Pennsylvania, killing all 40 on board, but none on the ground. It is thought that the flight was meant to hit the White House.

Last year, Dahl said of her husband and his passengers on United Flight 93: "They did what would almost never be asked of anyone. It's an unusually wonderful thing they did, their self-sacrifice."

According to USA Today, Jefferson County coroner's officials have confirmed Dahl's death, but the exact cause has not been released.