A pilot screaming "They're going to take us down!" as he stormed through his plane rambling about a bomb had to be tackled to the ground by passengers outside his cockpit.
The captain of JetBlue Airways Flight 191 from New York to Las Vegas was taken to a hospital after suffering a "medical situation" on board that forced the co-pilot to take over.
The pilot -- named as Clayton Osbon (49) -- seemed disoriented, jittery and constantly sipped water when he first marched through the cabin, then began to rant about threats linked to Iran, Iraq and Afghanistan after crew members tried to calm him down in the back, passengers said.
"They're going to take us down. They're taking us down. They're going to take us down. Say the Lord's prayer. Say the Lord's prayer," the captain screamed, according to passenger Tony Antolino.
Josh Redick, who was sitting near the middle of the plane, said the captain seemed "irate" and was "spouting off about Afghanistan and souls and al-Qa'ida."
Gabriel Schonzeit, who was sitting in the third row, said the captain said there could be a bomb on board the flight.
The captain was tackled by several passengers after he tried to re-enter the cockpit, which had been locked by the co-pilot. They sat on him for about 20 minutes until the plane landed at Rick Husband Amarillo International Airport in Texas.
Mr Antolino said after arriving in Las Vegas later: "Clearly he had an emotional or mental type of breakdown."
The captain was taken to a local medical facility after the plane landed, the airline said.
Earlier this month, an American Airlines flight attendant took over the public-address system on a flight bound for Chicago and spoke for 15 minutes about 9/11, saying "I'm not responsible for this plane crashing".
In 2008, an Air Canada co-pilot was forcibly removed from a Toronto-to-London flight, restrained and sedated after having a mental breakdown on a flight.
A flight attendant with flying experience helped the pilot safely make an emergency landing in Shannon.