San Diego authorities said Marc Duncan, 38, walked through an emergency door and onto the tarmac, then boarded a United Express plane Tuesday, CNN reported.
"He completely bypassed TSA screening," San Diego Harbor Police Chief John Bolduc said. "He was in a public area and went out an emergency fire door, which gave him access to the tarmac."
The emergency door alarm sounded and Bolduc said police arrived on the scene in 4 minutes. But Duncan managed to board the 30-seat United Express plane operated by SkyWest, which was bound for Los Angeles, airline spokesman Wes Horrocks said.
A flight attendant realized the plane had too many passengers, a passenger said, and the passengers got off the aircraft while their luggage was searched.
Duncan was identified and arrested, CNN said.
Duncan had been paroled from jail Monday night after serving time for theft, San Diego County Sheriff's Department records show.
He was being held in the San Diego jail and was scheduled to be in court Thursday.