United Airlines Flight 890 from Los Angeles landed as scheduled at Washington Dulles International Airport at 8:35 p.m., said Amy Kudwa, a Transportation Security Administration spokeswoman. No one was injured.
"This man came out of the bathroom, he was dressed in like an army suit. Full army gear," said passenger Naomi Rodriguez.
The passenger became unruly about 3½ hours into the flight from Los Angeles and was subdued by other passengers and federal air marshals.
"It happened so quickly, there was a passenger about six feet tall.
He just like jumped on top of him," Rodriguez said.
"After the passenger was restrained, the pilot decided to land at Dulles," United spokeswoman Megan McCarthy McCarthy said. "It wasn't an emergency landing."
Ken Wolfenberger, of Whittier, Calif., who was on the flight, told The Associated Press in a telephone interview that he helped subdue the unruly passenger. The man wore patches on his fatigues with special forces and jujitsu champion logos, Wolfenberger said.
The man had been acting strangely for about 20 minutes before the incident, then sat up, wrapped belts around his hands and threw punches into the air, Wolfenberger said.
Wolfenberger said he heard a flight attendant yell for help and tell the man, "Sir, get your hand off the handle."
"Any time you hear a flight attendant shout 'please help,' you worry that something pretty bad is going to happen," he said.
Wolfenberger said he got up to help, but by that time, the man was being held down and punched by other passengers. Wolfenberger grabbed the man's leg and held him down. Air marshals then came and took custody of the man.
Airport police and FBI agents met the flight and were interviewing the passenger, said FBI spokeswoman Debbie Wierman.
There were 138 passengers and six crew members on board, McCarthy said.