Investigators Seek Answers About Plane Crash That Followed Sonic Boom Scare

Federal authorities on Monday were investigating what caused a private aircraft to fly into restricted airspace over Washington, D.C., on Sunday, triggering a response by military jets that caused a sonic boom to be heard across much of the region before the small plane crashed in Virginia, killing all four people onboard.

The private business jet went down near Montebello, Va., the National Transportation Safety Board said. A spokeswoman for the Virginia State Police said in a statement on Monday that emergency responders were able to reach the wreckage on foot about four hours after receiving a report of a plane crash.

John Rumpel, who runs Encore Motors of Melbourne, a Florida-based company that owns the aircraft, said in a telephone interview on Monday that his daughter, Adina Azarian, his 2-year-old granddaughter, her nanny and the pilot were on the plane and did not survive.

The plane, a Cessna 560 Citation V, crashed “almost straight down and at a high speed,” he said, adding that the impact caused a crater, and the wreckage was spread over 150 yards. Mr. Rumpel had said on Sunday that they were returning home to East Hampton, N.Y., after a four-day visit to his home in North Carolina.

Fighter jets were sent from Joint Base Andrews in Maryland after the Cessna entered the restricted airspace, prompting the emergency response to intercept the flight, military and U.S. officials confirmed on Sunday.

After the Cessna flew into the restricted area, which includes important national landmarks, the Federal Aviation Administration called the pilot but received no response from that plane, and the military ordered the jets to intercept, a military official said.

The North American Aerospace Defense Command, or NORAD, which oversees aerospace control over the United States and Canada, said in a statement that two F-16 jets were deployed on Sunday to intercept the Cessna.

NORAD said that the fighter jets “were authorized to travel at supersonic speeds,” which would have produced the boom that was heard in the region, including in the suburbs of Virginia and Maryland. The jets also used flares that may have been visible from the ground, the agency said, “in an attempt to draw attention from the pilot.”

Officials later determined that the Cessna did not pose a threat, and the investigation will look into why the pilot did not respond to the F.A.A. The Cessna was not shot down, the officials said. A White House official said President Biden was briefed on the incident.

The Cessna crashed near the George Washington National Forest in Virginia, according to NORAD. The F.A.A. said the plane went down around 3:30 p.m.

Adam Gerhardt, an N.T.S.B. investigator, told reporters on Monday that the agency would be on the ground for at least three to four days. He said the wreckage was “highly fragmented,” and he described the area as rural and mountainous.

“It will be a very challenging accident site,” he said.

Mr. Gerhardt said the inquiry would look at when exactly the pilot became unresponsive and why the plane flew the route that it did. He said it was not yet known if the plane had a cockpit voice recorder or a flight data recorder, though he said the aircraft was not required to have such equipment.

“Everything is on the table until we slowly and methodically remove different components and elements that will be relevant for this safety investigation,” Mr. Gerhardt said.

Mr. Rumpel, who is also a pilot, said on Sunday that he had little information about the circumstances of the crash, but hoped his daughter, granddaughter and the others on board had not suffered. His voice breaking, he said that if the plane lost pressurization, “they all just would have gone to sleep and never woke up.”