Passengers were left stunned earlier after a pilot onboard a JetBlue flight out of New York forced the landing of his aircraft following an erratic outburst.

A co-pilot locked the pilot out the plane’s cockpit, before deciding to make an emergency landing in Amarillo, Texas.

Passengers helped to subdue the pilot after he attempted to re-enter the cockpit.

“The co-pilot became concerned that the captain exhibited erratic behaviour during the flight,” the Federal Aviation Administration (FAA) said in a statement.

The pilot was taken into custody on landing and is presently undergoing evaluation.

Following the incident on board Flight 191 an off-duty pilot entered the cockpit to assist the co-pilot, landing the Airbus SAS A320.

Some 135 passengers and five on-duty crew members were on board at the time.

The FAA, Federal Bureau of Investigation, Transportation Security Administration and local law enforcement authorities are investigating.