The pilot who took off from Roanoke Regional Airport on Monday without authorization after he threatened to crash into Smith Mountain Lake will likely not face any criminal charges.

However, the Federal Aviation Administration has opened an investigation to determine whether he violated federal regulations, said Jim Peters, a spokesman for the FAA.

The pilot, Samuel Shields, 50, of Blue Ridge landed safely back at the airport and was taken into custody after a nearly four-hour flight that had federal, state and local law enforcement officials on edge.

He was taken to an unspecified facility for a medical assessment, Roanoke police spokeswoman Aisha Johnson said.

Roanoke police will not place charges, Johnson said.

The FBI, which is investigating the incident, also has no plans to charge Shields, said Dee Rybiski, spokeswoman for the bureau's Richmond office.

Shields, a flight instructor and retired air traffic controller, took off from the airport about 10:50 a.m. Monday without communicating with air traffic controllers, said Sherry Wallace, a spokeswoman for the airport.

About the same time that air traffic controllers saw the Cessna 172 traveling down the runway, Roanoke police were notifying the airport of a 911 call the city had received from the pilot's wife, Wallace said.

Melinda Mayo, a Roanoke spokeswoman, declined to provide a copy of that 911 call, citing the FBI's ongoing investigation. But Wallace said the woman, who had dropped her husband off at the airport so he could do maintenance work on his plane, indicated that he was suicidal.

Franklin County Sheriff Ewell Hunt said Monday that the man's family told officials he had threatened to crash the plane in the lake.

After the plane took off, it disappeared from authorities' view because Shields was flying below radar and was not in communication with air traffic controllers, Wallace said. About an hour and a half into the flight, the tower established limited communication with the pilot.

The plane was seen over Smith Mountain Lake, Interstate 81, Read Mountain and the Botetourt County neighborhood where Shields lives.

Law enforcement officials asked people to evacuate from Bridgewater Plaza in Franklin County after the plane was seen there. A Virginia State Police helicopter that was shadowing the plane used a loudspeaker to urge residents of the Blue Ridge neighborhood to leave.

FBI agents eventually talked Shields into landing safely.

The FAA's investigation will be conducted by the Flight Standards District Office in Richmond and will determine whether any federal regulations were violated, Peters said.

He did not know how long the investigation would take.

When the investigation is complete, the FAA will hold a flight hearing. Depending on what the investigation reveals, the FAA could impose sanctions ranging from a letter of warning to revocation or suspension of the pilot's license or a civil penalty.

If sanctions are imposed, the pilot can choose to agree to the sanctions or appeal them to the National Transportation Safety Board, or take the issue to federal court for a trial.

The Shields family has asked Matt Broughton, president of a local pilots club and a partner with Gentry Locke Rakes and Moore law firm, to speak on their behalf.

Broughton said Tuesday that Shields is under medical care and that what happened Monday was a cry for help.

"He's struggling. That doesn't make him a bad pilot or a bad person. He's just going through some tough stuff," Broughton said.

Shields is an experienced and well-respected pilot within the local aviation community, Broughton said.

He believes that Shields will be able to fly again as long as he gets help.

"We're all looking forward to him getting better and getting back," he said.