Passengers on board a flight from New York wrestled the captain to the ground after he began yelling there was a bomb on board.
The co-pilot was forced to take over the controls and make an emergency landing in Texas, three-and-a-half hours into the flight.
The airline, JetBlue, later issued a statement saying there had been a "medical situation" onboard involving the captain, who has since been taken to hospital.
Some of the 135 passengers onboard flight 191 to Las Vegas said they saw the pilot storming through the aircraft, ranting about bomb threats, Iraq, Afghanistan and al-Qaida before cabin crew tried to calm him down at the back of the plane.
One news report said he shouted: "They’re going to take us down. They’re taking us down. They’re going to take us down. Say the Lord’s prayer."
When the captain then tried to re-enter the cockpit, which had been locked, four passengers pinned him to the ground, sitting on him until the plane landed safely at Amarillo airport in Texas.
JetBlue issued a statement saying an off-duty pilot who was a passenger on the flight took over the duties of the captain before the flight landed.
The FBI is coordinating an investigation with the airport police, Amarillo police, the Federal Aviation Administration and the Transportation Safety Administration.
By Linsey McNeill
