The attacker was eventually overpowered by passengers and pinned down with the help of other crew members. Police arrested the man after the plane landed at Boston International Airport.
The incident happened on a United Airlines flight from Los Angeles to Boston on Sunday. According to the public prosecutor's office, an alarm went off in the cockpit about 45 minutes before the planned landing, after which one of the doors of the machine was unlocked. A crew member checked the door and saw that the lever was about a quarter open.
A flight attendant then reported seeing the 33-year-old near the door and suspecting him. An exchange of words with the passenger followed. A short time later, the man attacked a crew member with a broken metal spoon.
The victim, whose gender was not specified, suffered "no serious injuries," United Airlines said. The airline said it would not tolerate any violence on board its aircraft. The attacker was no longer allowed to fly with United until the investigation was completed.
The man was brought before a judge in Boston after his arrest. He faces life imprisonment and a fine of up to $250,000 for attacking a plane crew member with a dangerous weapon.