The unresponsive plane that crashed after flying over restricted airspace was a private jet. How common are these accidents?

Many questions remain after an unresponsive plane crashed in Virginia after flying over restricted airspace in Washington, D.C. on Sunday. The plane, a Cessna 560 Citation V aircraft, was a private jet registered to a Florida-based company owned by John and Barbara Rumpel. John Rumpel has said his daughter, 2-year-old granddaughter and a nanny were on board. 

All three passengers and the pilot, who remained unresponsive during the ordeal, died and the plane crashed near George Washington National Forest in Virginia. The cause of the incident is being investigated by the Federal Aviation Administration and National Transportation Safety Board.