MONTEBELLO, Va. (CBS19 NEWS) -- The National Transportation Safety Board (NTSB) has arrived on the scene of a deadly plane crash near the Augusta County-Nelson County line.

A sonic boom shook the Washington, D.C.-metro area Sunday afternoon as fighter jets attempted to intercept the private jet flying in restricted airspace.

The jet was heading from Elizabethton, TN to Long Island, NY, when the pilot stopped responding, changed course and crashed two to three miles north of Montebello.

Florida businessman John Rumpel told the New York Times his daughter, two-year-old granddaughter and her nanny were on board. No one survived.

"When exactly did the pilot become unresponsive and why did the airplane fly the flight track that it did fly?" NTSB investigator Adam Gerhardt said.

He expects to spend three to four days on the ground investigation.

"But we'll be here as long as it takes. The wreckage is highly fragmented and in very, um, very rural and mountainous terrain. And it'll be a very challenging accident site," he said.

And, there’s a lot to sift through.

"The airplane, the engines, the weather conditions, pilot qualifications, the maintenance records," he said.

It's unknown if the plane has a black box.

CBS aviation safety analyst Robert Sumwalt gave one possible cause of the crash.

"This has the signatures of some sort of incapacitation ... the airplane does not pressurize properly, the pilot's become hypoxic, meaning of course, lack of oxygen. They fall asleep, as do the passengers, and because of a lack of oxygen, they perish. Meanwhile, the airplane continues," Sumwalt said.

Following the onsite investigation, the wreckage will go to a secure lab for more tests.

Gerhardt said the NTSB will issue a preliminary factual report within 10 days. The final report could take anywhere from one to two years.