JetBlue flight makes emergency landing in Texas
JetBlue flight 191 from New York to Las Vegas was carrying 135 passengers when a crew member had to be locked out of the cockpit and restrained.
Police and the FBI were called, but passengers later landed in Las Vegas.
JetBlue has said the pilot in charge of the plane decided to land at about 10:00 local time (16:00 GMT).
The flight touched down in Amarillo 10 minutes later, JetBlue said in a statement, and a new aircraft later arrived to take passengers on to Las Vegas.
Shocked and confused
On arrival in Las Vegas one passenger, David Gonzales, told US network ABC that he had grabbed the captain and put him in a headlock in an attempt to subdue him.
"I knew there were about 130 people on the plane... families, kids... and I thought, this is not going to happen on my plane," Mr Gonzalez said.
"We heard the word 'bomb'," passenger Heidi Karg told CNN. "We didn't know exactly what was going on."
Ms Karg said she heard the captain shout: "I need the code, gimme the code, I need to get in there."
According to Ms Karg, the pilot used the plane's public announcement system to call for someone to restrain the man. A number of male passengers were able to wrestle him to the ground, she said.
Another passenger, Grant Heppes, told the Associated Press that he saw a man in JetBlue uniform walk from the cockpit to the back of the plane. He was barred from going back in and then became disruptive.
"Once he got back to the front of the plane I heard him scream, 'Let me in!'" Mr Heppes said.
According to the Federal Aviation Administration, the pilot locked the man out of the cockpit after he began to show "erratic behaviour".
Mr Heppes said many passengers were "shocked and confused".
"Nobody was very loud except for the people trying to help out. Everybody just standing up and not really sure what was going on. It was very hard to tell," he said.
Stretcher Once on the ground in Amarillo the crew member was taken to a local medical facility and an off-duty captain who was on the flight by chance took over the role, JetBlue said.
According to Mr Heppes, the ambulance was parked beside the plane for about half an hour.
After the passengers had been taken off the plane, they were all interviewed by officials, Mr Heppes added.
One man at the airport, Shane Helton, told the Associated Press that emergency personnel were on the tarmac.
"They pulled one guy out on a stretcher and put him in an ambulance," he said.
The FBI is investigating the incident along with Amarillo police, airport police and US air and transport safety agencies, spokeswoman Lydia Maese in Dallas has told the Associated Press.
In 2008, an Air Canada co-pilot suffered a mental breakdown during a flight from Toronto to London. The co-pilot was sedated and the flight made an emergency landing in Ireland. All passengers on board were safe.