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As authorities responded to an unresponsive pilot flying a Cessna, a sonic boom rang out across DC, while officials were prompted to place the US Capitol complex on alert on Sunday afternoon. 

NORAD reported that it deployed F-16 fighter aircraft to intercept the plane, which was reported by the FAA as carrying four people before it later crashed in mountainous terrain near Montebello, Virginia. 

Both state and local law enforcement reached the crash site by foot after an hourslong search in the Staunton-Blue Ridge Parkway area, per an emailed statement sent from Virginia State Police spokesperson Corinne Geller on Sunday, which also added that "no survivors were located." 

The Federal Aviation Administration and the National Transportation Safety Board are both investigating the incident, which residents reported caused a "loud explosion" as the sonic boom occurred.

The incident prompted the DC Homeland Security and Emergency Management to tweet just after 3:30 pm: "We are aware of reports from communities throughout the National Capital Region of a loud 'boom' this afternoon. There is no threat at this time."

The boom was caused by an authorized Defense Department plane out of the Joint Base Andrews (JBA), where President Biden was playing golf with his brother, according to a pool report, stated officials in Maryland.

According to a White House official, Biden was briefed on the situation, per a pool report, adding that the sound from the authorized DOD aircraft was faint at JBA. 

A sonic boom is "an impulsive noise similar to thunder," according to the US Air Force. "It is caused by an object moving faster than sound — about 750 miles per hour at sea level," per the Air Force.